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MT BIOLOGY
TODAY | may ’14
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Dear Readers, The purpose of this xplore & Win is to develop curiosity amongst you about the biological wonders so that you can inculcate learning in an investigative manner. This section will amalgamate various biological concepts with their applications and will help you to develop analytical skills. Q1. “Chromosomal mutations may bring an evolutionary advantage.” Explain. Refer : Concept Map – Chromosomal mutations. Q2. Which property helps lysosome to remain stable despite of its constituents and how? Refer : High Yield Facts – GERL System. Q3. How does cell intake fluid materials having high molecular weight? Refer : High Yield Facts – GERL System. Q4. How do chondrocytes remain alive even though they are avascular? Refer : High Yield Facts – Animal Tissues-II. Q5. Discuss the role of myelinated nerve fibres in faster impulse conduction. Refer : High Yield Facts – Animal Tissues-II.
Q6. Cambium adds new cells towards centre or periphery yet itself remains single-layered. How? Refer : PMT Essential – Growth and Development in Flowering Plants. Q7. What is the difference between type of seed germination found in castor and in coconut? Refer : PMT Essential – Growth and Development in Flowering Plants. Q8. Discuss the phenomenon of antibiotic resistance in bacteria with respect to natural selection. Refer : CBSE Board – Solved Paper. Q9. ‘Disruptive selection may lead to speciation’. Explain. Refer : Concept Booster. Q10. How are the valves in the heart associated with heart sounds produced during one cardiac cycle? Refer : Concept Booster.
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MTBIOLOGY
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1. Two different animals are classified into the same family. This means that they would be classified in (a) the same phylum but different class (b) the same class but different species (c) a different kingdom and different phylum (d) a different class and different order. 2. The amount of DNA in a cell can be determined by measuring the fluorescence of a dye that binds in direct proportion to the amount of DNA. The histogram below represents the fluorescence of an eukaryotic germ cell during different stages of cell division (I, II, III, IV and V).
(a) Gram +ve eubacteria (b) Gram-ve eubacteria (c) all eukaryotes (d) both (a) and (b). 4. Sometimes a ladder-like structure observed in Spirogyra is formed due to (a) lateral conjugation (b) direct conjugation (c) scalariform conjugation (d) asexual reproduction. 5. Glyceraldehyde phosphate is oxidized during glycolysis. What happens to the hydrogen atom and the electron that are removed during oxidation? + (a) They reduce NAD . + (b) They oxidise NAD . (c) They are transferred to pyruvic acid. (d) They are eliminated in the form of methane. 6. Which of the following is an example of a conjugated protein? (a) Casein (b) Serum albumin (c) Globulin (d) Histones
Which of the following sequences represents the correct match of stages I-V with the division stages numbered 1 – 5? 1. Anaphase-I of meiosis 2. Anaphase-II of meiosis 3. Cytokinesis following telophase-II 4. Prophase-II of meiosis 5. Prophase-I of meiosis 1
2
3
4
5
(a)
II
IV
V
III
I
(b)
I
II
III
IV
V
(c)
V
IV
III
II
I
Case
(d)
IV
I
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3. The characteristic cell wall material peptidoglycan has another covering of lipopolysaccharides. This specialized condition is found in 6
7. Which of the following statements is incorrect? (a) During the process of exocytosis, the lumen (inner) surface of a secretory vesicle becomes the inside of the plasma (cell) membrane. (b) Cilia, microtubules and flagella are all associated with movement in cells. (c) A function of the nucleus is duplicating the genes for cell division. (d) Proteins that are to be secreted by cell are generally synthesized by ribosomes.
MT BIOLOGY
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8. Study the two cases carefully. The correct interpretation of the two cases is Mother
Father
Children
Case I
With disease
Normal Sons always with disease
Case II
With disease
Normal Sons and daughters could show disease
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MT BIOLOGY
TODAY | MAY ’14
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(a) Case I : X-linked recessive disease Case II : Autosomal recessive disease (b) Case I : Y-linked recessive disease Case II : X-linked recessive disease (c) Case I and II : X-linked recessive disease (d) Case I : X-linked dominant disease Case II : Autosomal dominant disease. 9. Last electron acceptor in ETS is (a) O2 (b) CoQ (c) cytochrome c (d) cytochrome a3. 10. Match column - I with column - II and select the correct option from the codes given below. Column - I Column - II (i) Bulliform cells A. Bean-shaped cells in stoma (ii) Guard cells B. Aerating pore (iii) Lenticel C. Accessory cell (iv) Subsidiary cell D. Modified adaxial epidermal cell along veins (a) (i) - D, (ii) - A, (iii) - B, (iv) - C (b) (i) - A, (ii) - D, (iii) - B, (iv) - C (c) (i) - D, (ii) - B, (iii) - C, (iv) - A (d) (i) - A, (ii) - B, (iii) - C, (iv) - D 11. Select the correct statement out of the following. (a) Healing of damaged tissue is because of the activity of sclerenchyma cells. (b) Grafting is difficult in monocot plants as they have scattered vascular bundles. (c) Because of marked climatic variations, plants growing near the sea shore do not produce annual rings. (d) The age of the plant can be determined by its height. 12. Out of 5 petals of a flower bud, two are completely internal, two are completely external and the remaining one is at its margin, internal as well as external. Identify this type of aestivation. (a) Imbricate (b) Valvate (c) Vexillary (d) Quincuncial 13. What differentiates PS I from PS II in photochemical reaction of photosynthesis? (a) Production of NADPH2 (b) Production of ATP (c) Being non-cyclic (d) All of the above 8
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14. In ripening tomatoes, photosynthetic chloroplast becomes non-photosynthetic (a) chromoplast (b) leucoplast (c) apoplast (d) symplast. 15. Acid rain is produced by (a) excess NO2 and SO2 from burning fossil fuels (b) excess production of NH3 by industries (c) excess release of CO by incomplete combustion (d) excess formation of CO 2 by combustion and animal respiration. 16. Auxin at an appropriate concentration can induce cell elongation in certain plant organs. However, tissues respond differently to different concentrations of auxin. Which graph best represents the IAA response of shoot and root?
(a)
(b)
(c)
(d)
17. When two different species associate with each other for the benefit of both, it is termed as positive interaction. Which of the following is generally not a positive interaction? (a) Flower and nectarivore (b) Plant and herbivore (c) Leguminous plant and nitrogen fixing bacterium (d) A lichen
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18. If you were outside for a long time on a hot, dry day, without anything to drink, which of the following would happen? (a) The production of thyroxine by thyroid gland would increase. (b) The osmotic pressure of blood would decrease. (c) The re-absorption of fluids from kidney tubules would decrease. (d) The secretion of anti-diuretic hormone from pituitary gland would increase.
(c) mRNA is polycistronic in both eukaryotes and prokaryotes (d) mRNA is monocistronic in both eukaryotes and prokaryotes 24. In the pedigree shown in the figure, individuals with the solid symbols suffer from a genetic disease caused by a recessive allele at an autosomal locus. You would counsel the couple marked A and B that the probability that each of their children will have the disease is
19. The given figure represents internal body plan of (a) Platyhelminthes (b) Nematoda (c) Annelida (d) Echinodermata.
20. The number of chromosomes present in the cells of the bread wheat Triticum aestivum suggest that it is (a) hexaploid (b) diploid (c) tetraploid (d) pentaploid.
25. Smoking induces degenerative changes in the lining of trachea. The epithelial cells most affected are (a) columnar (b) ciliated (c) glandular (d) stratified.
21. The figure shows the restriction enzyme cutting sites – (R1 - R3) in a wild type (n) and mutant (n ) gene.
26. Given diagram shows bone of the left human hindlimb as seen from front. It has certain mistakes in labelling. Two of the wrongly labelled bones are (a) tibia and fibula (b) femur and fibula (c) fibula and phalanges (d) phalanges and metatarsals.
If a radioactively labelled probe (that hybridizes at a sequence close to R1) is used for detecting the presence of DNA fragments after gel electrophoresis and Southern blotting, which of the following band patterns will you expect? (L1: wild type DNA, L2 : mutant DNA) (a)
(b)
(c)
(d)
22. A codon consists of 3 bases and there are of 4 different kinds of bases in a nucleic acid altogether. How many codons will be there? (a) 64 (b) 86 (c) 22 (d) 60 23. Select the correct statement out of following. (a) mRNA is polycistronic in eukaryotes and monocistronic in prokaryotes (b) mRNA is polycistronic in prokaryotes and monocistronic in eukaryotes 10
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(a) 0%
(b) 25% (c) 50% (d) 75%
27. Which of the following is incorrectly paired with its function? (a) Small intestine – enzymatic digestion of lipids, proteins and polysaccharides (b) Oesophagus – transports food from the mouth to the stomach (c) Large intestine – chemical breakdown of undigested starch, fats and amino acids (d) Stomach – mechanical and chemical digestion of food 28. Mammalian lungs have an enormous number of
minute alveoli (air sacs). This is to allow (a) more surface area for diffusion of gases (b) more space for increasing the volume of inspired air (c) more nerve supply to keep the lungs working (d) more spongy texture for keeping lung in proper shape.
29. The mammalian heart beat (a) stops when the nerve supply to the heart is cut (b) originates at the atrioventricular node (c) decreases when stretch receptors in the vena cava are stimulated (d) slows down when activity in the vagus nerve increases. 30. Vaccines produced through genetic engineering are safe as (a) they contain antigen only from coat of pathogen (b) they are least active form of virus (c) they are attenuated form of pathogen (d) all of the above. 31. Given below is a diagrammatic sketch of a portion of human male reproductive system. Select the correct set of the names of the parts labelled A, B, C, D.
(a) A-vas deferens, B-seminal vesicle, C-prostate, D-bulbourethral gland (b) A-vas deferens, B-seminal vesicle, C-bulbourethral gland, D-prostate (c) A-ureter, B-seminal vesicle, C-prostate, D-bulbourethral gland (d) A-ureter, B-prostate, C-seminal vesicle, D-bulbourethral gland 32. Read the following statements and select the correct
ones. (i) Medical termination of pregnancy (MTP) during first trimester is generally safe. (ii) Generally chances of conception are nil until mother breast-feeds the infant upto two years. (iii) Intrauterine devices like copper-T are effective contraceptives. (iv) Contraceptive pills may be taken upto one week after coitus to prevent conception. (a) (i) and (iii) (b) (i) and (ii) (c) (ii) and (iii) (d) (iii) and (iv) 33. In a car accident, a person has the sensory neurons
to his hand severed with no other damage being recorded. This person will
(a) regain feeling as the motor neurons will adapt and carry sensory impulses (b) be unable to feel and move his hand as feeling and movement is carried by the same neurons (c) regain feeling as the motor nerves replicate and replace the damaged neurons (d) be unlikely to regain feeling in the hand but will be able to move it. 34. A biologist sequenced the cytochrome-c enzyme in a range of animals and compared the amino acid (AA) differences between pairs of species. Which of the following results would be most consistent with modern systematics? Species Number of different amino acids (a) Chimpanzee/Rhesus monkey 23 Horse/Chimpanzee 2 Chimpanzee/Shark 8 (b) Chimpanzee/Rhesus monkey 23 Horse/Chimpanzee 23 Chimpanzee/Shark 23 (c) Chimpanzee/Rhesus monkey 12 Horse/Chimpanzee 8 Chimpanzee/Shark 3 (d) Chimpanzee/Rhesus monkey 2 Horse/Chimpanzee 12 Chimpanzee/Shark 23 35. Which of the following is correct order of the
evolutionary history of man? (a) Peking man, Homo sapiens, Neanderthal man, Cromagnon man (b) Peking man, Neanderthal man, Heidelberg man, Cromagnon man (c) Peking man, Heidelberg man, Neanderthal man, Cromagnon man (d) Peking man, Neanderthal man, Homo sapiens, Heidelberg man 36. Roots of which of the following species contain
valuable alkaloids that are useful in medicine? (a) Rauwolfia serpentina (b) Asparagus officinalis (c) Emblica officinalis (d) Helianthus annuus 37. On which part of the brain a ‘drunk person’ has the earliest effect? (a) Cerebrum (b) Pons varolii (c) Cerebellum (d) Medulla oblongata MT BIOLOGY
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38. If we completely remove the decomposers, from an ecosystem, its functioning will be adversely affected, because (a) energy flow will be blocked (b) mineral movement will be blocked (c) herbivores will not receive solar energy (d) rate of decomposition will be very high. 39. Read the following statements regarding replication of a DNA and transcription and select the correct ones. (i) During the replication even the introns are replicated, whereas introns are not transcribed during the process of transcription. (ii) Some of the bases that are incorporated during replication differ from those that are incorporated during transcription. (iii) There is no need of unwinding of strands during transcription, whereas replication process needs the unwinding of DNA strands. (iv) DNA-RNA hybrid is formed at some stage during both the processes. (a) (i) and (ii) (b) (ii) and (iii) (c) (iii) and (iv) (d) (ii) and (iv) 40. Match the following and select the correct option from the codes given below. A. LH (i) Antigonadal action B. Somatostatin (ii) Dispersion of melanin C. MSH (iii) Suppression of growth hormone D. Melatonin (iv) Formation of corpora lutea (a) A - (iii), B - (iv), C - (i), D - (ii) (b) A - (ii), B - (iii), C - (iv), D - (i) (c) A - (iv), B - (iii), C - (ii), D - (i) (d) A - (i), B - (iv), C - (ii), D - (iii) Direction : In the following questions (41-60), a statement of assertion (A) is followed by a statement of reason (R). Mark the correct choice as : (a) If both assertion and reason are true and reason is the correct explanation of assertion. (b) If both assertion and reason are true but reason is not the correct explanation of assertion. (c) If assertion is true but reason is false. (d) If both assertion and reason are false. 41. Assertion : As electrons move through photosystems, protons are transported across the membrane. Reason : Primary accepter of electron, located on 12
MT BIOLOGY
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outer side of membrane, transfers its electron to a H– carrier while removing the proton. 42. Assertion : Alpha - diversity is also known as within community diversity. Reason : It is dependent upon species richness and evenness. 43. Assertion : Active water absorption by roots needs metabolic energy. Reason : Passive water absorption by roots occurs in response to transpiration. 44. Assertion : Photorespiration is a wasteful process in C3 plants. Reason : During photorespiration, no energy is produced and 25% of fixed CO2 is lost. 45. Assertion : Ovule has a protective envelope called integument. Reason : Integument encircles the ovule completely. 46. A ssertion : Nuclear endosperm is formed by subsequent nuclear division without wall formation. Reason : Coconut is an example of such endosperm, where the endosperm remains nuclear throughout the development of the fruit. 47. Assertion : Cytokinins are antisenescent. Reason : Cytokinins have been found to induce flowering in certain species of plants. 48. Assertion : Primary succession takes a very long time. Reason : Succession taking place after forest fire is called primary succession. 49. Assertion : Use of weedicides affects photosynthetic ability of plants. Reason : Weedicides are metabolic inhibitors. 50. Assertion : In human, insulin is synthesised as a prohormone. Reason : Pro-hormone needs to be processed before it becomes a fully mature and functional hormone. 51. Assertion : In coelenterates, the arrangement of cells is complex. Reason : The cells performing the same functions are arranged into the tissues. 52. Assertion : The cells of columnar epithelium at absorptive surfaces often bear microvilli on their free ends. Reason : Microvilli enhance surface area for absorption.
53. Assertion : Thyroid gland is a ductless gland. Reason : Thyroid gland directly pours its secretion i.e. thyroxine, into the blood. 54. Assertion : The normal heart rate is 72/min and the duration of cardiac cycle is 0.8 sec. Reason : The duration of cardiac cycle is inversely proportional to the heart rate. 55. Assertion : The space between the seminiferous tubules is occupied by Sertoli cells. Reason : Sertoli cells secrete testosterone hormone. 56. Assertion : Head of the sperm consists of acrosome and mitochondria. Reason : Acrosome contains spiral row of mitochondria. 57. Assertion : Excessive amounts of calcitonin hormone in the blood causes softening of bones. Reason : Calcitonin causes mobilisation of calcium from the bones to the blood plasma. 58. Assertion : Lac operon is an example of inducible operon system. Reason : In this, the product of gene activity, if already present, stops the activity of concerned gene. 59. Assertion : Disruptive selection reduces variation and does not promote evolutionary change. Reason : This selection favours average sized individuals. 60. Assertion (A) : Test cross is a type of back cross Reason (R) : Test cross is used to know whether an individual is homozygous or heterozygous. Answer key 1. (b) 6. (a) 11. (c) 16. (a) 21. (c) 26. (d) 31. (a) 36. (a) 41. (a) 46. (c) 51. (a) 56. (d)
2. 7. 12. 17. 22. 27. 32. 37. 42. 47. 52. 57.
(a) (a) (d) (b) (a) (c) (a) (a) (b) (b) (a) (d)
3. 8. 13. 18. 23. 28. 33. 38. 43. 48. 53. 58.
(b) (a) (a) (d) (b) (a) (d) (b) (b) (c) (a) (c)
4. 9. 14. 19. 24. 29. 34. 39. 44. 49. 54. 59.
(c) (a) (a) (b) (c) (d) (d) (d) (a) (a) (b) (d)
5. 10. 15. 20. 25. 30. 35. 40. 45. 50. 55. 60.
(a) (a) (a) (a) (b) (a) (c) (c) (c) (b) (d) (b) nn MT BIOLOGY
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Direction : In the following questions (1-75), a statement of assertion (A) is followed by a statement of reason (R). Mark the correct choice as : (a) If both assertion and reason are true and reason is the correct explanation of assertion. (b) If both assertion and reason are true but reason is not the correct explanation of assertion. (c) If assertion is true but reason is false. (d) If both assertion and reason are false. 1. Assertion : In living organisms, increase in mass and increase in number of individuals are twin characteristics of growth. Reason : Multicellular organisms grow by cell division or multiplication. 2. Assertion : Viruses take over the host machinery to replicate themselves. Reason : Viruses are non-cellular organisms characterised by an inert crystalline structure. 3. Assertion : Sexual reproduction in liverworts takes place by gemmae. Reason : Gemmae are green, multicellular, sexual buds, which develop in small receptacles called gemma cups located on the thalli. 4. Assertion : Aschelminthes are called pseudocoelomates. Reason : In Aschelminthes, the mesoderm is present as scattered pouches in between the ectoderm and endoderm. 5. Assertion : The fruit of the Solanaceae family is called legume. Reason : Legume fruit develops from a inferior bicarpellary and bilocular ovary having parietal placentation. 6. Assertion : Both apical meristem and intercalary meristem are called primary meristems. Reason : These meristems appear early in life of a plant and helps in the formation of primary plant body. 14
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7. Assertion : The intestine of earthworm between 27 segment and upto 23-35 segments infront of anus contains internal median fold of dorsal wall called typhlosole. Reason : Typhlosole increases the effective area of absorption in the intestine of earthworm. 8. Assertion: Endoplasmic reticulum, Golgi complex, lysosomes and vacuoles together form the endomembrane system. Reason : Functions of these organelles are coordinated, so they are considered together as a system. 9. Assertion : Collagen is the most abundant protein in the whole biosphere. Reason : Collagen is present in almost all animal and plant cells. 10. Assertion : Enzymes generally function in a narrow range of temperature. Reason : Low temperature renders the enzyme in a temporarily inactive state and high temperature destroys enzymatic activity. 11. Assertion : G1 phase corresponds to the interval between mitosis and initiation of DNA replication. Reason : During G1 phase, cells are metabolically inactive. 12. A ssertion : Pinus seeds cannot germinate and establish without the presence of mycorrhizae. Reason : The fungus provides minerals and water to the roots and roots provide sugars and N-containing compounds to the mycorrhizae. 13. A ssertion : Enterogastrone is also called gastric inhibitory peptide (GIP). Reason : It inhibits gastric secretion and motility and slows down gastric contraction. 14. Assertion : Pons region of the brain moderates the functions of the respiratory rhythm centre. Reason : Respiratory rhythm centre is present in the medulla region of the brain. 15. Assertion : Heart is autoexcitable, but its functions can be modified by neural signals.
Reason : Sympathetic nerves decrease the rate of heart beat and parasympathetic nerves increase the rate of heart beat. 16. Assertion : Urine is a light yellow coloured water fluid with a slightly acidic pH. Reason : Urine contains the pigment urochrome, which is a breakdown product of haemoglobin from worn out red blood corpuscles. 17. Assertion : The portion of the myofibril between two successive 'Z' lines is called a sarcomere, which is the functional unit of contraction. Reason : The junction between a sensory neuron and the sarcolemma of the muscle fibre is called the neuromuscular junction. th th th 18. Assertion : The 8 , 9 and 10 pairs of ribs of our body are called vertebrochondral or false ribs. Reason : These ribs do not articulate directly with the sternum, but join the seventh rib with the help of cartilage. 19. Assertion : Membrane of a non-conducting neuron is positive on the outside and negative inside. Reason : At rest, the axonal membrane is comparatively + more permeable to sodium ions (Na ) and nearly + impermeable to potassium ions (K ). 20. Assertion : Thyroid hormones of thyroid gland control the metabolism of carbohydrates, proteins and fats. Reason : Thyroid gland secretes a proteinaceous hormone called parathyrocalcitonin, which regulates the metabolism. 21. Assertion : The innermost wall layer of macrosporangium is called tapetum. Reason : Tapetum nourishes the developing embryo in the ovule. 22. Assertion : Rhizomes, present in ginger, take part in vegetative propagation. Reason : Rhizomes are underground adventitious roots which can form new plants. 23. Assertion : The secondary growth occurs in most of the dicotyledonous roots and stems. Reason : Secondary growth increases the girth of the organs by the activity of the vascular cambium and cork cambium. 24. Assertion : FSH acts on Sertoli cells of epididymis to secrete an androgen binding protein (ABP) and inhibin. Reason : ABP concentrates testosterone in epididymis and inhibin suppresses FSH synthesis. 25. Assertion : Mendel's law of segregation is also known as principle of purity of gametes.
Reason : The segregation of the two Mendelian factors of a trait results in gametes receiving only one factor out of a pair. 26. Assertion : Ranunculus flabellaris shows heterophylly with dissected leaves inside water and entire leaves outside. Reason : Changes in the phenotype in response to different environmental factors is due to plasticity. 27. Assertion : Split genes are the segments of DNA which can move from one place in the genome to other. Reason : Split genes possess repetitive DNA, either similar or inverted, at their ends which aid in movement. 28. Assertion : Stems of some plants of arid region carry out photosynthesis. Reason : Stem of these plants are modified into flattened or fleshy cylindrical structures which contain chlorophyll. 29. Assertion : Marijuana is a product obtained from hemp plant. Reason : It is obtained from the dried flowers and top leaves of the female plants of Cannabis sativa. 30. Assertion : Meristem culture is the cultivation of axillary or apical shoot meristems. Reason : Meristem culture involves the development of an already existing root meristem and subsequently the generation of shoots from developed roots. 31. A ssertion : Dosa and Idli are the fermented preparations of rice and black gram. Reason : CO2 produced during fermentation causes puffing up of the dough. 32. Assertion : Endonucleases remove nucleotides from the ends of the DNA. Reason : Exonucleases makes cuts at specific positions within the DNA. 33. A ssertion : "Rosie", the first transgenic cow, produced human protein enriched milk. Reason : The milk contained the human alphalactalbumin and was more balanced product for human babies than natural cow milk. 34. Assertion : Outcrossing is the best breeding method for animals that are below average in milk production. Reason : Outcrossing involves mating of superior males of one breed with females of another breed. 35. Assertion : Vertical distribution of different species occupying different levels is called stratification. Reason : Trees occupy top vertical strata, shrubs the second, herbs and grasses occupy the bottom layers.
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36. Assertion : The sharp decline in dissolved oxygen in the water body, causes mortality of fish and other aquatic creatures. Reason : Micro-organisms involved in bio-degradation of organic matter in the receiving water body consume a lot of oxygen. 37. Assertion : Colostrum provides active immunity to new born infant. Reason : It contains IgD as the major immunoglobulin. 38. Assertion : The concentration of ozone over Antarctica is decreasing leading to thinning of ozone layer. Reason : Ozone depleting substances react with ozone present in troposphere and destroy the same. 39. Assertion : Diaphragms, cervical caps and vaults are inserted into the female reproductive tract to cover the cervix during coitus. Reason : They prevent conception by blocking the entry of sperms through the cervix. 40. Assertion : Labia majora are two large fleshy folds of skin which form the boundary of vulva. Reason : Labia majora are homologous to membranous urethra of male. 41. Assertion : The central cell is the largest cell of the embryo sac. Reason : It has a highly vacuolate cytoplasm, which is rich in reserve food and Golgi bodies. 42. A ssertion : In organisms exhibiting internal fertilisation, the male gamete is motile. Reason : In such organisms, the number of sperms produced is large. 43. Assertion : Grasshopper represents XO type of sex determination. Reason : In grasshopper, males have only one X-chromosome besides the autosomes, whereas females have a pair of X-chromosomes. 44. Assertion : The RNA polymerase l transcribes rRNAs except 5S rRNA. Reason : The RNA polymerase III transcribes tRNA, 5SrRNA and some snRNAs. 45. Assertion : The thorns and tendrils of Bougainvillea and Curcurbita show homology. Reason : Both structures arise in the axillary position. 46. Assertion : B-lymphocytes produce antibodies that regulate humoral immunity. Reason : Humoral immunity provides defence against all pathogens including fungi and protozoa. 47. Assertion : The germplasm is evaluated so as to identify plants with desirable combination of characters. 16
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Reason : The entire collection of plants/seeds having all diverse alleles for all gene is called germplasm. 48. Assertion : The large holes in Roquefort cheese are due to production of large amount of CO2 by a bacterium called Propionibacterium sharmanii. Reason : The Swiss cheese are ripened by growing a specific fungi on them, which gives them a particular flavour. 49. Assertion : Adenosine deaminase (ADA) deficiency cannot be cured completely by enzyme replacement therapy. Reason : The permanent cure for this disease is the gene isolation from bone marrow cells producing ADA and its introduction into cells at early embryonic stages. 50. A ssertion : Primary succession takes very long time. Reason : Soil is absent at the time of beginning of primary succession. 51. Assertion : A glycosidic bond is formed by linkage of individual monosaccarides. Reason : Formation of glycosidic bond leads to loss of a water molecule. 52. Assertion : Sickle-cell anaemia can be transmitted from parents to offspring when both the partners are carriers for the gene or when one is carrier and other has the disorder. Reason : Sickle-cell anaemia is an autosomal dominant disorder. 53. Assertion : Parthenocarpy can be induced in fruits through the application of growth hormones. Reason : Parthenocarpic fruits develop without fertilization and are seedless. 54. Assertion : A widely used diagnostic test for AIDS is enzyme linked immunosorbent assay (ELISA). Reason : Western blotting test is employed for confirmation of ELISA negative cases. 55. Assertion : Logistic growth model of population is considered more realistic. Reason : Resources for growth for most animal populations are finite and become limiting sooner or later. 56. Assertion : Cell growth causes disturbance in the ratio between nucleus and cytoplasm. Reason : Cell division restores the nucleo-cytoplasmic ratio following growth. 57. Assertion : The symplastic movement of water occurs exclusively through intercellular spaces and walls of the cells.
Reason : The symplast system of adjacent cell walls is continuous throughout the plant, except at the casparian strips of endodermis in roots. 58. Assertion : Vasopressin is also called as anti-diuretic hormone (ADH). Reason : Vasopressin stimulates the reabsorption of water and electrolytes by the distal convoluted tubules and thereby reduces loss of water through urine. 59. Assertion : The pancreatic juice contains inactive enzyme trypsinogen which acts on proteins in its active form. Reason : Trypsinogen is activated into active trypsin by an enzyme, enterokinase secreted by the intestinal mucosa. 60. Assertion : The F1 head piece is an integral membrane protein complex and contains the site for synthesis of ATP from ADP and inorganic phosphate. Reason : The F0 is a peripheral membrane protein complex that forms the channel through which protons cross the inner membrane. 61. Assertion : Gibberellin is also called as the stress hormone. Reason : Its production is stimulated by drought, water logging and other adverse environmental conditions. 62. Assertion : Hatch and Slack pathway is also known as C4 pathway. Reason : In C4 plants, first stable photosynthetic product is 4-carbon phosphoglyceric acid. 63. Assertion : Presence of large amounts of nutrients in water causes algal bloom. Reason : Algal bloom causes deterioration of the water quality and may lead to fish mortality. 64. Assertion : The openings of the right and the left ventricles into the pulmonary artery and the aorta respectively are guarded by the semilunar valves. Reason : These valves in the heart allow the flow of blood in both the directions. 65. Assertion : The descending limb of loop of Henle is impermeable to water but permeable to electrolytes. Reason : The glomerular filtrate dilutes as it passes down the descending limb of loop of Henle. 66. Assertion : Synovial joints help in locomotion and many other movements. Reason : Synovial joints are characterised by the presence of a fluid-filled synovial cavity between the articulating surfaces of the two bones. 67. Assertion : Cochlea is the organ of hearing. Reason : The organ of Corti is located on the basilar membrane inside cochlea and contains hair cells that act as auditory receptors.
68. Assertion : The common ascomycetes are mushrooms, bracket fungi or puffballs. Reason : Ascomycetes grow in soil, on logs and tree stumps and in living plant bodies as parasites. 69. Assertion : Adipose tissue is a type of loose connective tissue located mainly beneath the skin. Reason : The cells of adipose tissue are specialised to store fats. 70. Assertion : ZIFT is useful for females who cannot produce ovum. Reason : ZIFT involves transfer of zygote, formed inside donor, into the Fallopian tube of the recepient. 71. Assertion : Placenta acts as a temporary endocrine tissue. Reason : Placenta produces hormones such as hCG, LH, relaxin and progesterone. 72. Assertion : RNAi takes place inside all prokaryotic organisms as a method of cellular defense. Reason : RNAi involves silencing of tRNA which prevents translation. 73. Assertion : Pyramid of energy is always upright. Reason : When energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step. 74. Assertion : In codominance, both alleles are expressed in a heterozygous condition. Reason : In codominance, alleles blend to produce a new phenotype. 75. Assertion : Visceral muscles show alternate light and dark striations. Reason : The light bands contain myosin whereas dark bands contain actin. Answer key 1. (b) 6. (a) 11. (c) 16. (a) 21. (d) 26. (a) 31. (b) 36. (a) 41. (b) 46. (c) 51. (b) 56. (b) 61. (d) 66. (a) 71. (c)
2. 7. 12. 17. 22. 27. 32. 37. 42. 47. 52. 57. 62. 67. 72.
(b) (b) (a) (c) (c) (d) (d) (d) (b) (b) (c) (d) (c) (a) (d)
3. 8. 13. 18. 23. 28. 33. 38. 43. 48. 53. 58. 63. 68. 73.
(d) (a) (a) (a) (b) (a) (b) (c) (a) (d) (b) (a) (b) (d) (a)
4. 9. 14. 19. 24. 29. 34. 39. 44. 49. 54. 59. 64. 69. 74.
(a) (d) (b) (c) (d) (a) (c) (a) (b) (b) (c) (b) (c) (b) (c)
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5. 10. 15. 20. 25. 30. 35. 40. 45. 50. 55. 60. 65. 70. 75.
(d) (a) (c) (c) (a) (c) (a) (c) (a) (a) (a) (d) (d) (d) (d) nn
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Q.1.What is silent area in human brain?
– B.M. Bodhankar, Nagpur
Ans. Until recently, the prefrontal areas of human brain were referred to as the “silent areas” or “uncommitted cortex”, because injury to these regions was not accompanied by sensorimotor signs, and the function of these areas was not clear. Prefrontal cortex or PFC, the latest evolutionary addition to the mammalian brain, (especially the humans), has long been known to endow qualities that differentiate human beings from all other animals. PFC was for some years, known to perform executive function, but now it has been demonstrated that its functions include the ability to organize behavioural response to solve a complex problem (including strategies used in learning information and searching memory). Moreover, it has been found to be involved in other behaviours such as moral judgement, appreciation of jokes, evaluating rewards, awareness, temperament, meditation, etc. Thus, far from being “silent”, “uncommitted” or known just for “psychial functions”, the PFC is comprised of a set of control systems, each with the separate target, i.e., different prefrontal areas control different activities that are separately localised. Q.2.How do transposons or jumping genes move?
– B.M. Bodhankar, Nagpur
Ans. Transposable elements or transposons are stretches of DNA that usually have repeated DNA segments at their ends and can jump within the genome, hence, are also known as jumping genes. They were discovered by Barbara Mc Clintock in corn plants (maize). She proposed that the kernel mosaics, which result from breaks at particular site at chromosome 9, were produced by the factor called Ds (for dissociation). However, this factor is incapable of inducing chromosome breakage by itself and requires another factor, Ac (for activator). Both Ac and Ds are members of a family of transposable elements. These elements are structurally related to each other and can insert at many different sites in chromosomes; hence also known as controlling elements. Transposase, a protein synthesised by Ac elements, is involved in transposition. 18
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Genetic analysis has provided some information about the mechanism whereby Ac (and presumably Ds) elements transpose. Initially, the element is replicated by normal cellular machinery. Then one copy of Ac transposes ahead of the replication fork. When replication process is finished, there will be two sister chromatids, one with single copy of Ac (in the new location only) and one with two copies (one in new location and one in the old). The actual transposition of an Ac element is considered to be non-replicative because it is replicated during normal replication mechanism and not transposition. Studies with diverse organisms, including bacteria, fungi, nematodes, insects, plants and mammals, suggest that transposable elements are widespread. These elements exhibit considerable variations in structure and function.
Q.3. Glycolysis and Krebs’ cycle generate energy without oxygen, then what is the role of oxygen in aerobic respiration? – B.M. Bodhankar, Nagpur
Ans. Aerobic respiration starts by breaking glucose down into pyruvate by glycolysis. Next, in a preparatory step for the Krebs’ cycle, coenzyme A joins to pyruvate causing a loss of one carbon and the generation of NADH. The acetyl CoA formed enters Krebs’ cycle and the acetyl group is transferred to a molecule of oxaloacetic acid making a molecule of citric acid which enters the cycle. The Krebs’ cycle releases CO2 and high energy molecules NADH and FADH2, which are converted into ATP by the mitochondrial electron transport chain (ETC). Oxygen acts the terminal electron acceptor in ETC. If there is no oxygen to accept electrons, the ETC stops working and NADH and FADH2 cannot be converted back into NAD and FAD; hence glucose biochemical pathway stops. Moreover, substrate-level phosphorylation occurs during glycolysis and Krebs’ cycle and yields a relatively small amount of ATP. The generation of ATP from chemiosmosis at the end of ETC is called oxidative phosphorylation because when oxygen acts as terminal electron acceptor, there is a maximal amount of free energy released. Hence, more protons can be transported, which means that a greater charge buildup occurs across the inner mitochondrial membrane leading to synthesis of ATP. This process, thus, generates relatively large amount of ATP for the cell as compared to substrate – level phosphorylation.
Q.4. Organs like liver and kidney are transplanted very often. Is it possible to transplant legs? – Komal Mohanty, Cuttack
Ans. Yes, it is possible to transplant legs, however within the field of transplants, there are fewer vascularized composite transplants than other organ transplants performed every year. The area of vascularized composite allotransplantation comprises the vascularised transplantation of multiple tissues such as skin, muscle, bone, nerve and tendon as a functional unit. Unlike the other organ transplants, leg transplants are little controversial mainly because of two reasons. Firstly, the prosthetic devices provide sufficient support successfully without the risk and complications of taking immuno-suppressive medications, and secondly, the sensation takes longer to return in case of transplanted leg which is not required in case of prostheses. However, there are potential benefits of such transplantation which entail restoration of body image, recovery of sensation and its connection to the brain. Another advantage is the ability to perform daily activities which are not possible with prostheses. Following transplantation, medications such as immuno-suppressants are required to successfully prevent rejection of transplants. These do have sideeffects and people react differently to some drugs but ultimately the decision of transplantation needs addressing of the balance between the risks of immuno-suppression versus the benefits of receiving a quality of transplant. Q.5. How can we transplant a tissue or organ from an animal to human? What problems may arise in such a transplant?
– Komal Mohanty, Cuttack
Ans. Any procedure that involves the transplantation, implantation, or infusion into a human recipient of either live cells, tissues, or organs from a non-human animal source or human body fluids, cells, tissues or organs that have had ex-vivo contact with live non-human cells, tissues, or organs, is referred to as xenotransplantation. In the light of the lack of supply of human organs for transplantation several alternatives including xenotransplantation have been investigated and debated. There are major issues with such a transplantation as transplanting solid organs from animal sources into humans results in rapid loss of xenograft because of hyperacute rejection. In this immunologic reaction, preformed antibodies
(xenoreactive natural antibodies) circulating in human blood bind to vascular epithelium of the animal organ and trigger a cascade that quickly results in thrombosis of the graft. If the transplanted organ is not rejected within minutes to hours, a more delayed type of immunologic response ultimately leads to thrombosis of the graft within hours to days. This process is known as delayed xenograft rejection or acute vascular rejection. The use of xenotransplantation products also carries a natural and expected risk of transmitting infectious pathogens, this is called xenosis. A range of various approaches are investigated and proposed to circumvent xenograft rejection. Genetically engineered animals have been designed to downregulate expression of various immunogenic substances which constitute donor-based strategies. Secondly, there are recipient based strategies in which complement cascade can be interrupted therapeutically by using several inhibitory agents. Severe immune-modulating therapies have been developed to prolong xenograft survival. Because of xenosis, all major reports on xenotransplantation have recommended comprehensive monitoring and surveillance of xenograft recipient. Ethical, religious, and consensual matters are required be addressed for successful research in xenotransplantation. Q.6. What are stem cells? What is their role in human body? – Komal Mohanty, Cuttack
Ans. Stem cells are undifferentiated cells in the body that can differentiate into specialised cells and can divide to produce more stem cells. In addition, they serve as internal repair system, dividing essentially to replenish other cells. In mammals, two broad types of stem cells have been identified, namely, embryonic stem cells, isolated from the inner cell mass of the blastocysts, and non-embryonic or adult stem cells which are found in various tissues. For adult stem cells there are three accessible sources: bone marrow, adipose tissue and blood. These can also be taken from umbilical cord blood just after the birth. Stem cells are distinguished from other cell types by two important characteristics. First, they are able to differentiate into specialised cell types under certain physiologic or experimental conditions. Second, their ability to go through numerous cycles of cell division while maintaining the undifferentiated state. They are widely studied, for their potential therapeutic use. Researches made another break through by identifying conditions that would allow some MT BIOLOGY
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specialised adult stem cells to be “reprogrammed” genetically to assume stem-cell like state. These are called induced pluripotent stem cells (iPSCs). Given its miraculous properties, medical research believe that stem cell therapy has the potential to dramatically revive treatment of many human diseases. Q.7. Why do autoimmune diseases occur more commonly in women?
- Bharati, Assam
Ans. Autoimmune diseases occur when the immune system begins attacking its own tissues rather than external pathogens. They affect ~8% of the population, 7578% of whom are women. The basic immune response between men and women has been known to differ. Women produce a more vigorous immune response and increased antibody production. Sex hormones, such as estrogen, testosterone, and progesterone are believed to mediate many of the sex-based differences in the immune response and to account for sex differences in the prevalence of autoimmune diseases. Recently, estrogen and androgens have been found to directly influence whether Th1 or Th2 type immune response develops by interacting with hormone receptors on immune cells. Moreover, cytokine receptors such as IL-1R, IL-18R have been discovered on hormone producing tissues which suggest bidirectional regulation of the immune response. Furthermore, proinflammatory cytokines such as TNF-a and IL-1b stimulate the release of glucocorticoids from the hypothalamus- pituitary -adrenal axis, which regulates the inflammatory process, along with increase in estrogens.
Generally, the occurrence of overt autoimmune disease, as opposed to the presence of autoimmune antibodies in the blood, depends on a balance between the incorrectly functioning systems, and the body’s ability to regulate them. It is possible that pregnancy and childbirth may leave women more susceptible to these conditions than men. It also seems that genetics play another important role in occurrence of autoimmune diseases.
Q.8. Why do people die of drug overdose?
- Bharati, Assam
Ans. Drug overdose is ingestion or application of a drug or other substance in quantities greater than recommended. Every drug behaves differently in each person’s body and central nervous system, interacting with their unique body chemistry and underlying health conditions. For instance, a toxic dose of heroin increases the inhibitory effect of GABA (g-amino butyric acid), a neurotransmitter, which causes breathing to slow and eventually stop. Nicotine present in cigarettes can also kill by overdose. At high concentration, nicotine binds to receptors both in the brain and on muscles leading to paralysis of muscles that control breathing or to heart attack. Stimulants such as cocaine and methamphetamine trigger the release of norepinephrine which causes increased activity, increased heart rate and blood pressure. Their overdose most commonly causes heart attack, hyperthermia and brain damage. In many cases, people who die of overdose are under influence of more than one drug whose synergistic effects are often lethal. nn
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GENERAL INSTRUCTIONS (i) All questions are compulsory. (ii) The question paper consists of four sections A, B, C and D. Section-A contains 8 questions of 1 mark each, Section B is of 10 questions of 2 marks each, Section C is of 9 questions of 3 marks each whereas Section D is of 3 questions of 5 marks each. (iii) There is no overall choice. However, an internal choice has been provided in one question of 2 marks, one question of 3 marks and two questions of 5 marks weightage. A student has to attempt only one of the alternatives in such questions. (iv) Wherever necessary, the diagrams drawn should be neat and properly labelled. (v) The question paper will include value based question to the extent of 3-5 marks.
SECTION - A 1. Write the name of the organism that is referred to as the ‘Terror of Bengal’. [From Excel in Biology, Page 20, Q. 4] 2. What are ‘true breeding lines’ that are used to study inheritance pattern of traits in plants? 3. Name any two types of cells which act as ‘cellular barriers’ to provide innate immunity in humans. 4. Mention the type of host cells suitable for the gene guns to introduce an alien DNA. [From Excel in Biology, Page 427, Q. 6] 5. How is ‘stratification’ represented in a forest ecosystem? 6. Give an example of an organism that enters ‘diapause’ and why? 7. Identify ‘a’ and ‘b’ in the figure given below representing proportionate number of major vertebrate taxa.
8. State the cause of accelerated eutrophication. [From Excel in Biology, Page 420, Q. 16] SECTION - B 9. Why do algae and fungi shift to sexual mode of reproduction just before the onset of adverse conditions? [From Biology Today - March ‘14, Page 5, Q. 1] 10. A cross was carried out between two pea plants showing the contrasting traits of height of the plant. The result of the cross showed 50% of parental characters. (i) Work out the cross with the help of a Punnett square. (ii) Name the type of the cross carried out. 11. How does the gene ‘I ’ control ABO blood groups in humans? Write the effect the gene has on the structure of red blood cells. [From Excel in Biology, Page 115, Q. 3] OR
Write the types of sex-determination mechanisms the following crosses show. Give an example of each type.
(i) Female XX with Male XO (ii) Female ZW with Male ZZ MT BIOLOGY
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12. (i) Name the scientist who suggested that the genetic code should be made of a combination of three nucleotides. (ii) Explain the basis on which he arrived at this conclusion. [From Excel in Biology, Page 446, Q. 21] 13. State the disadvantage of inbreeding among cattle. How it can be overcome? [From Excel in Biology, Page 273, Q. 11] 14. Explain with the help of a suitable example the naming of a restriction endonuclease. 15. State how has Agrobacterium tumifaciens been made a useful cloning vector to transfer DNA to plant cells. [From Excel in Biology, Page 305, Q. 5 (SA); Biology Today - March ‘14, Page 5, Q. 6] 16. Construct an age pyramid which reflects a stable growth status of human population. 17. Apart from being part of the food chain, predators play other important roles. Mention any two such roles supported by examples. [From Excel in Biology, Page 356, Q. 14] 18. How are ‘sticky ends’ formed on a DNA strand? Why are they so called? [From Excel in Biology, Page 306, Q. 22]
SECTION - C
19. Explain any three advantages the seeds offer to angiosperms. [From Excel in Biology, Page 44, Q. 44(ii); Biology Today - March ‘14, Page 5, Q. 9] 20. Name and explain the role of inner and middle walls of the human uterus. 21. A colourblind child is born to a normal couple. Work out a cross to show how it is possible. Mention the sex of this child. OR Mendel published his work on inheritance of characters in 1865, but it remained unrecognized till 1900. Give three reasons for the delay in accepting his work. 22. Women are often blamed for producing female children. Consequently, they are ill treated and ostracized. How will you address this issue scientifically if you were to conduct an awareness programme to highlight the values involved? [From Excel in Biology, Page 460, Q. 1(i); Biology Today - Sept ‘13, Page 8, Q. 30] 22
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23. (a) Name the tropical sugarcane variety grown in South India. How has it helped in improving the sugarcane quality grown in North India? [From Excel in Biology, Page 269, Q. 6; Biology Today - Nov ‘13, Page 13, Q. 13] (b) Identify ‘a’, ‘b’ and ‘c’ in the following table : Crop
Variety
1.
Brassica
2.
Flat bean Pusa Sem 2 Pusa Sem 3
3.
(c)
Pusa Gaurav
Pusa Sawani Pusa A-4
Insect Pests (a) (b) Shoot and fruit borer
[From Excel in Biology, Page 273, Q. 14; Biology Today - Nov ‘13, Page 13, Q. 17] 24. Why are beehives kept in crop field during flowering period? Name any two crop fields where this is practiced. 25. How did the process of RNA interference help to control the nematode from infecting roots of tobacco plants? Explain. From Excel in Biology, Page 327, Q. 6 (SA); Biology Today - March ‘14, Page 6, Q. 15] 26. Study the graph given below and answer the questions that follow: [From Excel in Biology, Page 433, Q. 9]
(i) Write the status of food and space in the curves (a) and (b). (ii) In the absence of predators, which one of the two curves would appropriately depict the prey population? (iii) Time has been shown on X-axis and there is a parallel dotted line above it. Give the significance of this dotted line. 27. (i) What is primary productivity? Why does it vary in different types of ecosystems? (ii) State the relation between gross and net primary productivity. [From Excel in Biology, Page 469, Q. 6]
SECTION - D 28. (a) Coconut palm is monoecious, while date palm is dioecious. Why are they so called? [From Excel in Biology, Page 18, Q. 1; Biology Today - March ‘14, Page 6, Q. 19(i)] (b) Draw a labelled diagram of sectional view of a mature embryo sac of an angiosperm. [From Excel in Biology, Page 44, Q. 15 (i)] OR (a) How is ‘oogenesis’ markedly different from ‘spermatogenesis’ with respect to the growth till puberty in the humans ? [From Excel in Biology, Page 71, Q. 9] (b) Draw a sectional view of human ovary and label the different follicular stages, ovum and corpus luteum. [From Excel in Biology, Page 72, Q. 2] 29. (a) Explain the process of DNA replication with the help of a schematic diagram. [From Excel in Biology, Page 151, Q. 13] (b) In which phase of the cell cycle does replication occur in eukaryotes ? What would happen if cell-division is not followed after DNA replication? OR (a) Explain Darwinian theory of evolution with the help of one suitable example. State the two key concepts of the theory. [From Excel in Biology, Page 469, Q. 20] (b) Mention any three characteristics of Neanderthal man that lived in Near East and Central Asia. 30. (a) Name the technology that has helped the scientists to propagate on large scale the desired crops in short duration. List the steps carried out to propagate the crops by the said technique. (b) How are somatic hybrids obtained? [From Excel in Biology, Page 270, Q. 2] OR (a) Cancer is one of the most dreaded diseases of humans. Explain ‘contact inhibition’ and ‘metastasis’ with respect to the disease. [From Excel in Biology, Page 240, Q. 70 and 71; Biology Today - March ‘14, Page 5, Q. 4] (b) Name the group of genes which have been identified in normal cells that could lead to cancer and how they do so?
(c) Name any two techniques which are useful to detect cancers of internal organs. [From Excel in Biology, Page 428, Q. 16] (d) Why are cancer patients often given a-interferon as part of the treatment? SOLUTIONS 1. Water hyacinth (Eichhornia crassipes) is referred to as the ‘Terror of Bengal’. 2. True breeding lines are those plants that have been generated through repeated self-pollination. They show stable trait inheritance and expression for several generations. 3. Certain types of leukocytes (WBCs) like polymorphonuclear leukocytes (PMNL-neutrophils) and natural killer cells in the blood are cellular barriers, which provide innate immunity in humans. 4. Undifferentiated plant cells are the most suitable host cells for the gene gun to introduce an alien DNA. It is because plant cells have rigid cell wall which can be easily broken down by bombarding them with high velocity micro-particles of gold or tungsten coated with DNA. 5. Vertical distribution of different species occupying different levels is called stratification. Trees occupy top vertical strata or layer of a forest, shrubs occupy the second level and herbs and grasses occupy the bottom layers. 6. Bombyx mori (silk moth) is an insect that enters diapause. It enters into diapause due to some adverse environmental conditions such as drought, extreme temperature, reduced food availability; which, in turn, delays the overall development. The physiological and metabolic activities diminish at this particular time. 7. (a) Mammals (b) Amphibians. 8. Eutrophication is the natural aging of a lake or water bodies by nutrient enrichment of water. Apparently pollutants from mans’s activities like effluents from the industries and homes have radically accelerated this aging process. This phenomenon is called accelerated eutrophication. The major causes are : (i) Sewage, agricultural and industrial wastes, the prime contaminants are nitrates and phosphates, which act as plant nutrients; (ii) Heated (thermal) waste water flowing out of electricity generating units e.g. thermal power plants. 9. Organisms, such as fungi and algae, switch to sexual mode of reproduction during adverse conditions because MT BIOLOGY
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10. Two contrasting characters of height are tall and dwarf. In the given cross, if 50% of the progeny shows parental characters, then it must be a cross between a heterozygous tall and a homozygous recessive dwarf parent.
14. The convention for naming restriction enzymes is that the first letter of the name comes from the genus and the next two letters come from the species of the prokaryotic cell from which they were isolated, e.g., EcoRI comes from Escherichia coli RY 13. In EcoRI, the letter ‘R’ is derived from the name of strain. Roman numbers following the names indicate the order in which the enzymes were isolated from that strain of bacteria.
(i) Parent :
15. Refer answer 5, Pg. No. 307, ‘MTG - Excel in Biology’.
sexual reproduction brings variation into the individuals, some of which might help the individuals to adapt to the changed conditions and survive. This ensures the continuity of species.
Tall
Dwarf
Genotype :
Tt
Gametes :
T
F1 generation :
t t
× tt
t
t
T Tt Tall
t tt Dwarf
Tt Tall
tt Dwarf
t
Phenotypic ratio ⇒ Tall : Dwarf = 1 : 1
(ii) This type of cross is known as test cross. 11. Refer answer 29, Pg. No. 474, ‘MTG - Excel in Biology’. OR (i) The type of sex determination mechanism shown in female XX with male XO is called male heterogamety because male produces two different types of gametes.
Example - Drosophila
(ii) The type of sex determination mechanism shown in female ZW with male ZZ is female heterogamety because female produces two different types of gametes.
Example - Birds
12. (i) George Gamow suggested that the genetic code should be made up of three nucleotides. (ii) He proposed that since there are only 4 bases and if they have to code for 20 amino acids, the code should constitute a combination of bases made up of three nucleotides. Combination of 43 (4 × 4 × 4) would generate 64 codons; generating many more codons than required.
17. Refer answer 14, Pg. No. 358, ‘MTG - Excel in Biology’. 18. Refer answer 22, Pg. No. 309, ‘MTG - Excel in Biology’. 19. Seeds offer several advantages to angiosperms: (i) Seeds have better adaptive strategies for dispersal to new habitats and hence spread their own species. (ii) The hard seed coat provides protection to the young embryo from harsh environmental conditions. (iii) Being products of sexual reproduction, they generate new genetic combinations leading to variations. 20. The inner glandular wall of the uterus is known as endometrium. Role - During the menstrual cycle, the endometrium wall grows into a thick, vascular (blood vessel-rich) glandular layer. This condition of the endometrium favours the implantation of the foetus. If fertilisation does not occur, the endometrium is shed during the hemorrhagic phase of the menstrual cycle. The middle wall of the uterus is known as myometrium. Role - It consists of smooth muscles. It brings about contraction while delivery of the baby.
13. Continuous inbreeding among cattle leads to reduced fertility and productivity, a phenomen on called inbreeding depression.
21. Colourblindness is a X- linked recessive disorder which shows transmission from carrier female to male progeny and hence, usually males are affected and females remain carriers.
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16. The bell-shaped age pyramid reflects a stable growth status of human population. It can be represented as follows:
It can be overcome by mating selected animals with unrelated superior animals of same breed. MT BIOLOGY
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If the given couple is normal with a colourblind child, their genotypes will be
Parents :
Male XY ×
Gametes :
X
Progeny : X
Y
Xc X cX Carrier female
Female Xc X Xc
X XX Normal female
X
XY X cY Colourblind male Normal male Hence, a colourblind male child is born to the given couple. OR The following are the three reasons that led to the delay in acceptance of Mendel’s work: (i) Lack of communication and publicity in those days. (ii) His concept of factors (genes) as stable and discrete units that controlled expression of traits and, of the pair of alleles that did not blend with each other was not accepted in the light of variations occurring continuously in nature. (iii) Mendel’s approach to explain biological phenomenon with the help of mathematics was also not accepted. 22. Refer answer 1(i), Pg. No. 462, ‘MTG - Excel in Biology’. 23. (a) Tropical sugarcane grown in South India is Saccharum officinarum. It has thicker stems and higher sugar content but did not grow well in North India. Saccharum barberi was originally grown in North India, but had poor sugar content and yield. These two species were successfully crossed to get sugarcane varieties combining the desirable qualities of high yield, thick stems, high sugar content and ability to grow in North India. (b) (a) Aphids (b) Jassids, Aphids and fruit borer (c) Okra (Bhindi) 24. Bees, while collecting nectar from flowers, transfer the pollen grains. Beehives are kept in a crop field during flowering period to enhance the pollination of the crop, which increases the crop yield. Also, bees can easily collect huge amounts of nectar from the flowers of the crop in a close reach without much foraging. This increases honey production. This technique is practised in apple and watermelon field. 25. Refer answer 6, Pg. No. 329, ‘MTG - Excel in Biology’. 26. (i) There is ample food and space for the population depicted by the curve (a). When the resources are unlimited, the curve is exponential. There is limiting food and space for the population depicted by the curve (b). When the resources are limiting, the curve becomes sigmoid. Y
(ii) In the absence of predators, curve (a) would appropriately depict the prey population. (iii) The dotted line represents the carrying capacity of the environment. The carrying capacity represents the size of population that the environment can hold by providing necessary resources. When a population reaches this line its population size is stabilised by various environmental factors. 27. (i) Primary productivity is the rate at which radiant energy is stored by photosynthetic and chemosynthetic activity of producers. It is expressed in terms of (gm–2 yr–1) or (kcal m–2 yr–1). It varies in different types of ecosystems, because it depends upon plant species of the area, their photosynthetic capacity, availability of nutrients, solar radiations, precipitaion, soil type and a number of other environmental factors. (ii) Refer answer 6, Pg. No. 471, ‘MTG - Excel in Biology’. 28. (a) Refer answer 1, Pg. No. 19, ‘MTG - Excel in Biology’ (b) Refer answer 17, Pg. No. 47, ‘MTG - Excel in Biology’. OR (a) Refer answer 9, Pg. No. 75, ‘MTG - Excel in Biology’. (b) Refer answer 12, Pg. No. 68, ‘MTG - Excel in Biology’. 29. (a) Refer answer 13, Pg. No. 158, ‘MTG - Excel in Biology’. (b) In eukaryotes, the replication of DNA takes place at S-phase of the cell-cycle. The replication of DNA and cell division cycle should be highly coordinated. A failure in cell division after DNA replication results into polyploidy (a chromosomal anomaly). OR (a) According to Darwin, evolution took place by natural selection. The rate of appearance of new life forms depends upon their life span and their ability to multiply. There is intense competition and struggle to ensure living to obtain maximum amount of food and space. The variations occurring in organisms are gradual and inheritable and the species fit to survive the most leaves more offsprings. The nature selects the individuals, which are most fit to adapt to their environment. Hence, the population’s characteristics change, giving rise to the evolution of new life forms. Thereby, the two key concepts of the theory are: (i) Branching descent : According to this concept, various species have come into existence from a common ancestor. (i) Natural selection : According to this concept, nature selects the individuals, which are most fit to adapt to MT BIOLOGY
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their environment. The fitness, according to Darwin, refers ultimately and only to reproductive fitness. Hence, those who are better fit in an environment, leave more progeny than others. These, therefore, will survive more and hence are selected by nature. He called this natural selection and implied it as a mechanism of evolution. An example of natural selection is the antibiotic resistance in bacteria. When a bacterial population was grown on an agar plate containing antibiotic penicillin, the colonies that were sensitive to penicillin dies, whereas one or few bacterial colonies that were resistant to penicillin survived. This is because these bacteria had undergone chance mutation, which resulted in the evolution of a gene that made them resistant to penicillin drug. Hence, the resistant bacteria multiplied quickly as compared to the non-resistant (sensitive) bacteria, thereby increasing their number. Hence, the advantage of an individual over the other helps in the struggle for existence. (b) Characteristics of Neanderthal man: (i) They possess a brain capacity of 1400 cc. (ii) They walked upright and had low brows, receding jaws and high domed heads. (iii) They used hides to protect their body and bury the dead. 30. (a) The technique that has helped scientists to propagate the desired crops in short duration is tissue culture. Plant tissue culture can be defined as the maintenance and growth of plant cells, tissues and organs on a suitable culture medium in vitro (in a test tube).
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The basic technique of plant tissue culture involves the following steps : (i) Preparation of suitable nutrient medium and storage into suitable containers. (ii) Selection of explants such as shoot tip and sterlisation by disinfectants. (iii) Inoculation (transfer) of the explants into the suitable nutrient medium under sterile condition. (iv) Growing the culture in the growth chamber or plant tissue culture room, having the appropriate physical condition i.e., artificial light (16 hours of photoperiod), temperature (–26°C) and relative humidity (50- 60%). (v) Regeneration of plants from cultured plant tissues and hardening. (vi) After hardening, plantlets are transferred to the green house or field conditions following acclimatization of regenerated plants. (b) Refer answer 2, Pg. No. 271, ‘MTG - Excel in Biology’. OR (a) Refer answer 70 and 71, Pg. No. 247, ‘MTG - Excel in Biology’. (b) Several genes called cellular oncogenes (c-onc) or proto oncogenes have been identified in normal cells which, when activated under certain conditions, could lead to oncogenic transformation of the cells. (c) Refer answer 16, Pg. No. 429, ‘MTG - Excel in Biology’. (d) The cancer patients are given substances called biological response modifiers such as a-interferon which activates their immune system and helps in destroying the tumor. nn
Connective tissue • Connective tissue, formed from mesoderm of the embryo, is the most abundant and widely distributed tissue of the body. • This tissue provides the structural framework and support to different tissues and helps in body defense, repair, fat storage, etc. Components of connective tissue • Three components are present in the connective tissue, namely, matrix ground substances, cells (fixed and wandering) and fibres which are explained with the figure on the next page.
• The most common cell types are fibroblasts, which
produce fibres and other intercellular materials. The two most common types of fibres are: collagen (collagenous) and elastic. Collagen fibres are for strength while the elastic ones are for elasticity of the tissue. Both the cells and the fibres are embedded in the intercellular substance. • The proportion of the cell, fibres, and intercellular substance vary, depending on a particular nature and function of the connective tissue. For example, a strong connective tissue needs greater proportion of the collagen fibres and fewer cells. MT BIOLOGY
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Fibres Reticular fibres are strong and form a branching network. They are made up of reticulin protein.
Collagen fibres are thick, straight or wavy, and often form bundles. They are very strong, resist stretching and are made up of collagen protein.
Elastic fibres are slender, unbranched, and very stretchy. They recoil to their original length after stretching or distortion. They are formed of elastin protein.
Fixed Cells
Wandering Cells
A melanocyte is a fixed pigment cell that synthesizes melanin, a brownish-yellow pigment.
A plasma cell is an active, mobile immune cell that produce antibodies.
A fixed macrophage is a stationary phagocytic cell that engulfs cell debris and pathogens.
Free marophages are wandering, phagocytic cells that patrol the tissue, engulfing debris or pathogens.
Mast cells are fixed cells that stimulate local inflammation and mobilize tissue defenses.
Mesenchymal cells are mobile stem cells that participate in the repair of damaged tissues.
Fibroblasts are fixed cells that synthesize the extracellular fibres of the connective tissue.
Neutrophils are small, mobile, phagocytic blood cells that enter tissues during infection or injury.
Adipocytes (fat cells) are fixed cells that store lipid reserves in large intracellular vesicles.
Lymphocytes are mobile cells of the immune system. Red blood cell in vessel
Ground substance fills the spaces between cells and surrounds connective tissue fibres. In all forms of connective tissue proper, ground substance is clear, colorless, and viscous due to the presence of proteoglycans and glycoproteins.
Types of connective tissue • The connective tissue can be classified into three types as given in flowchart below:
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Loose connective tissue • Loose connective tissue has cells loosely arranged in a
semi-fluid ground substance. Types of loose connective tissue are as described below:
Adipose tissue
Reticular tissue
Structure
It takes the form of fine threads crossing each other in every direction leaving small spaces called areolae. It consists of ground substance, the matrix, white and yellow fibres and cells like fibroblasts, mast cells, macrophages (= histocytes or clasmatocytes), lymphocytes, plasma cells, mesenchyme cells, chromatophores. Fat cells can be seen in small groups.
It is a fat storing connective tissue. The adipose tissue consists of several spherical or oval adipose cells (= adipocytes or fat cells). Each adipose cell contains fat globules, due to which the nucleus and the cytoplasm are displaced to the periphery. These cells are often called signet ring cells.
This tissue consists of star-shaped reticular cells whose protoplasmic processes join to form a cellular network. The reticular fibres are present on the reticular cells. They are composed of a protein called reticulin. Matrix and some other cells such as macrophages, lymphocytes and adipose cells are also present.
It is present under the skin as subcutaneous tissue in between and around muscles, nerves and blood vessels in submucosa of gastrointestinal tract and respiratory tract, in the bone marrow, between the lobes and lobules of compound glands and in mesenteries and omenta.
The adipose tissues are found in the subcutaneous tissue, around the heart, kidneys, eyeballs, mesenteries and omenta, where fat is stored.
Reticular connective tissue is present in the liver, spleen, lymph nodes, thymus, tonsils, bone marrow and lamina propria of the gut wall.
The primary function of areolar tissue is to bind parts together. Other functions are to provide strength, elasticity, support to the parts where this tissue is present. It also provides rapid diffusion of materials and migration of wandering cells towards areas of infection and repair.
The adipose tissue is chiefly a food reserve or ‘fat depot’ for storage. The subcutaneous fat prevents heat loss from the body and also rounds off the body contour sheet. It forms a shock-absorbing cushion around the eye balls and kidneys.
The reticular connective tissue is especially adapted to provide strength and support and it forms the supporting framework (stroma) of many organs. It also helps to bind together the cells of smooth muscles. The reticular cells are phagocytic and form defence mechanism of the body.
Diagrammatic representation
Function
Areolar tissue
Location
Table: Types of loose connective tissue
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White fat and brown fat There are two types of adipose tissue — white (or yellow) fat and brown fat. White fat contains large adipose cells, each having a single fat globule (monolocular). The cytoplasm is pushed to a peripheral layer containing nucleus. On the other hand, brown fat contains adipose cells with several small fat globules (multilocular). They contain a large number of mitochondria. Brown fat has a role in non-shivering thermogenesis in newborn infants. It is located in the regions of neck and shoulders, spine and chest. This adipose tissue is responsive to thyroid hormones, epinephrine and the sympathetic nervous system. It also contains large amounts of uncoupling proteins which uncouple oxidation from phosphorylation making metabolism less efficient (less ATP is generated). The major product of this inefficient metabolism is heat which contributes in maintaining body temperature in infants.
fibres, making it stronger than loose connective tissue. It is of two types : dense irregular connective tissue and dense regular connective tissue. • Dense irregular tissue has fibroblasts and many fibres (mostly collagen) that are oriented differently. This type of connective tissue produces tough coverings that package organs, such as capsules of kidneys and adrenal glands. It also covers muscle as epimysium, nerves as perineurium and bones as periosteum. • Dense regular connective tissue has collagen fibres present in rows between many parallel bundles of fibres. It is of two types as discussed in the table below:
Dense connective tissues • Dense connective tissue contains tightly packed collagen Table: Types of dense regular connective tissue White fibrous connective tissue
Function
Cords
The white fibrous connective tissue forms cords called The yellow elastic connective tissue forms cords tendons, which connect the skeletal muscles with called ligaments which join bones to bones. the bones.
Sheets
Type
Structure
It consists of mainly white (collagen) fibres which This tissue is mainly made up of much thicker are arranged in bundles. The fibroblasts are present in branched loose network of yellow elastic fibres. rows between the bundles. The fibroblasts are irregularly scattered.
The sheets formed by this tissue occur in the dermis The sheets formed by this tissue occur in the walls of the skin, connective tissue sheaths of muscles and of blood vessels, lungs, bronchioles, true vocal nerves and tunica adventitia of large blood vessel, cords, cartilage of larynx and trachea. periosteum, perichondrium, pericardium, duramater and renal capsule, etc. It has great strength, however its flexibility is This tissue has considerable strength and limited. The presence of white fibrous tissue at the remarkable elasticity. Thus, it allows stretching joints between skull bones makes them immovable. of various organs.
Specialised connective tissue The special connective tissue cartilage, bone and blood – each have unique cells and extracellular matrices that allow specialized functions. I. Cartilage • Cartilage is a soft skeletal tissue. It is not rigid like bone. • It is found more abundantly in vertebrate embryo 30
Yellow elastic connective tissue
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because most of the bones forming skeleton of the adult are cartilaginous in the early stage. Structure of cartilage • A typical cartilage consists of cartilage cells and ground
substance (matrix). (i) Cartilage cells or chondrocytes : They are present in a fluid-filled space, called lacunae within the cartilage ground substance. Young cartilage cells
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(chondroblasts) are small and flattened whereas mature cartilage cells (chrondrocytes) are large and rounded. (ii) Ground substance (matrix) : It essentially consists of water, proteoglycans, some lipid, collagen, non-collagenous protein and fibres. The core protein is aggrecan. Carbohydrates are glucosaminoglycans (GAG) including chondroitin sulphate, keratin sulphate and hyaluronic acid.
Chondrocytes remain alive, even though there are no blood vessels in the cartilage matrix, because they receive oxygen and nutrients by diffusion through ground substance from surrounding blood vessels. This diffusion can only occur because cartilage matrix is not calcified. Types of cartilage • The cartilage is divided into three types as shown in the table below :
Table : Types of cartilage Elastic cartilage
It contains clear, large amount of transluscent, The matrix is firm and has slightly elastic matrix with less fibres. abundant white fibres. White fibrous cartilage is the strongest cartilage.
The matrix contains numerous yellow fibres which form a network by uniting with one another. It is most flexible.
It is the most prevalent cartilage. It forms It occurs in the intervertebral articular surfaces at the joints of long bones disc, and in the pubic such as knees, where it is called articular symphysis. cartilage. It also forms part of larynx and sternum (breast bone), rings of trachea and bronchi, sternal parts of ribs (= costal cartilages), hyoid apparatus and nasal cartilages.
This type of cartilage is found in the pinna and external auditory canal of the ear, Eustachian tube, epiglottis and tip of the nose.
Figure
Structure
Fibrous cartilage
Location
Hyaline cartilage
II. Bone • Bone is a solid, rigid and strong connective tissue which gives support to various organs. • A dried bone is a bone which has been exposed to drying conditions for a long time so that all living cells die, decay and disappear. The bone then contains only inorganic matrix. • A decalcified bone is obtained when a bone is kept in dilute acid (HCl or HNO3) for long hours due to which calcium, magnesium, potassium and sodium salts of inorganic part of matrix get dissolved whereas organic
part of matrix remains intact. Structure of mammalian bone • It consists of four parts : (i) Periosteum : Periosteum is a thick and tough sheath of collagen that forms an envelop around the bone. Bundles of periosteal collagen fibres, called Sharpey’s fibres, penetrate the bone matrix to provide a firm connection between the two. The periosteum contains blood vessels and bone-forming cells, the osteoblasts which produce new bone material. MT BIOLOGY
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Types of bone cells Osteoblasts : Secrete collagen fibres and matrix (ground substance) of bone and are responsible for the calcification of the matrix. They retain the ability to divide and communicate by thin cytoplasmic processes which form gap junctions. When an osteoblast is completely surrounded by the matrix, it is called an osteocyte. Osteocytes : Inactive bone cells or bone forming cells. They are responsible for maintaining the matrix and can both secrete and resorb matrix. Osteoclasts : Formed by fusion of monocytes, destroy bone matrix. They release lysosomes, organic acids and hydrolytic enzymes to break down, the bone matrix. (ii) Matrix : The matrix is tough, containing both inorganic and organic substances. It consists of ossein protein (30%-35%) and mineralisation occurs by calcium phosphate salts (65%-70%). The Haversian canals, a characteristic feature of the mammalian bones, are present in the matrix. It contains an artery, a vein, a lymph vessel, a nerve, and some bone cells packed in connective tissue. These canals are interconnected by transverse channels called Volkmann’s canals. The matrix of the bone are present as layers called lamellae. The lamellae are of four types: –– Haversian lamellae : These lamellae occur around the Haversian canals. A Haversian canal with its surrounding lamellae and osteocytes constitute a cylindrical unit of bone called Haversian system or osteon. Haversian systems are absent in spongy bones of mammals. –– Interstitial lamellae : These lamellae occur between the Haversian systems. –– Outer circumferential lamellae (outer concentric lamellae) : These lamellae occur inner to periosteum. –– Inner circumferential lamellae (inner concentric lamellae) : These lamellae occur outer to endosteum. (iii) Endosteum : It is present outer to the bone marrow cavity and comprises of white fibrous tissue and osteoblasts (bone forming cells). Because of presence of osteoblasts in both periosteum and endosteum, above can grow both from outside and inside i.e., growth of bone is bidirectional. (iv) Bone marrow : In long bones, a cavity is present inner to endosteum called as bone marrow cavity. Marrow cavity of long bones is filled with a soft neurovascular connective tissue (areolar, adipose 32
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and blood vascular) called bone marrow. Bone marrow is of two types:
Types of bones • On the basis of its texture, a bone is of two types : compact and spongy (cancellate).
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Table : Types of bones Compact bone Location
In the shaft (diaphysis) of long bones.
Spongy bone In the epiphyses of long bones.
Lamellae Arranged to form Haversian system.
Arranged irregularly, lamellae form trabeculae.
Bone marrow
Yellow; stores fat
Red; produces RBCs
Bone marrow cavity
Narrow
Broad
Nature
Hard and compact
Spongy
Ossification and calcification Ossification (or osteogenesis) is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in the formation of normal, healthy bone tissue. Intramembranous ossification is the direct laying down of bone into the primitive connective tissue (mesenchyme), while endochondral ossification involves cartilage as a precursor (hyaline cartilage). In fracture healing, endochondral ossification is the most commonly occurring process, for example in fractures of long bones treated by plaster of Paris, whereas fractures treated by open reduction and stabilization by metal plate and screws may heal by intramembranous ossification. Endochondral ossification is one of the two essential processes during fetal development of mammalian skeletal system by which bone tissue is created. Osteoporosis Osteoporosis is a bone disease where parts of the bone become weak and prone to fracture. This condition is more common in seniors, but can affect men and women of all ages as the weakened bones can no longer support their body weight. The bones in our bodies are constantly being broken down and replaced with new bones. This bone-building cycle takes about 100 days and is influenced by the hormones produced in our bodies (such as estrogen in women) as well as by the levels of calcium and vitamin D. Osteoporosis occurs when bone tissue and minerals are lost faster than the bone is replaced, i.e., osteoblastic activity is less than normal.
The rate of bone loss increases significantly after menopause because the ovaries stop producing estrogen, a hormone that plays a major role in the bone repair process. Estrogen inhibits osteoclastic (bone resorption) activity in the bone and therefore stimulates bone growth. Female athletes and women who suffer from anorexia nervosa may also be at increased risk for osteoporosis. In both cases, the menstrual cycle is disrupted or lost and levels of estrogen in the body drop dramatically. Women who experience early menopause (before the age of 45 years) are more likely to have osteoporosis. III. Blood • Blood is a mobile, fluid connective tissue which is derived from mesoderm. • It is of reddish colour that flows inside blood vessels by means of pumping activity of heart. • An adult human contains 5.0 – 5.5 litres of blood. • Blood is composed of a watery fluid called plasma and floating bodies termed formed elements (blood corpuscles). • Plasma is a complex liquid component of the blood, about 90% of which is formed by the water alone. Dissolved in the plasma are several organic and inorganic substances including proteins, glucose, cholesterol, urea, hormones, vitamins, and inorganic salts and fibrinogen. It also contains anticoagulant, heparin. • Formed elements or blood corpuscles are of the three types : erythrocytes, leucocytes and thrombocytes (discussed in the table given on the next page). • Lymph is a mobile connective tissue made plasma and lymph corpuscles. • Lymph plasma is similar to that of blood but have fewer blood proteins, less calcium and phosphorus and high glucose concentration. Main proteins are globulins which are actually antibodies. • Lymph corpuscles are floating amoeboid cells, mostly lymphocyte. RBC’s and platelets are absent in lymph.
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Table : Types of blood cells Description
Erythrocyte
• It is circular, biconcave,
denucleated, has homogenous cytoplasm with haemoglobin; cell organelles such as ER, mitochondria, ribosomes, centrioles are absent. • It transports of oxygen and some amount of carbon dioxide.
Agranulocyte
Leucocytes Lymphocyte • It has a large rounded nucleus and its cytoplasm lacks granules. • It is motile, non-phagocytic and secretes antibodies; helps in healing. Monocyte
Eosinophil
• It has bilobed nucleus, and
coarse granules in cytoplasm. It takes acidic stain. • It is non-phagocytic, has antiallergic properties, and plays role in immunity.
Granulocytes
Blood cell
Basophil
• The nucleus is usually
Neutrophil
• It has many lobed nucleus,
fine granules in cytoplasm and it takes acidic as well as basic stains. • It is phagocytic, engulfs germs and dead cells.
• It is the largest of all types
of leucocytes. Nucleus is bean shaped, has enough cytoplasm. • It is motile, phagocytic, i.e., engulfs germs and cell debris, often changes into macrophages.
three lobed, there are less number of coarse granules in cytoplasm. It takes basic stain. • I t r e l e a s e s h e p a r i n , histamine and serotonin
Platelets
ATTENTION COACHING INSTITUTES:
• They are colourless, rounded or
oval, non-nucleated fragments of the cells. • They help is blood clotting.
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Muscular Tissue • Muscular tissue constitutes the muscles, made up of myocytes, (muscle cells) which are in the form of contractile fibres varying in lengths. • Muscular tissue in general develops from the mesoderm of the embryo but the muscles of the iris of the eye and myoepithelial cells of the salivary, mammary and sweat glands arise form the ectoderm of the embryo. • The special property of muscular tissue is contractility i.e., the cells of muscular tissue can shorten considerably and return to the original relaxed state. The muscle cells contract in a definite direction. • Another property of muscle is the electrical excitability. It is due to the energy stored in the electrical potential difference across the plasma membrane. Structure of muscles • About 85% of the mass of a muscle is made up of muscle fibres; the remaining 15% is mostly connective tissue. • Muscle is organized and largely shaped by the connective tissue, which is composed of a ground substance, collagen, and recticular and elastin fibers
of varying proportions. • In muscle, the connective tissue is largely responsible
for transmitting forces, for example the transmission of forces from the muscle to the bone by the tendon. • The connective tissues’ elasticity and distensibility help to ensure that the tension developed by the muscle is smoothly transmitted and that a muscle will return to its original shape after being stretched. Thus, the connective tissue of a muscle provides a framework for the concept of series and parallel elastic components within a muscle. • There are three levels of muscle tissue organization : epimysium, endomysium, and perimysium. These three levels are a consequence of differing sizes and orientations of connective tissue fibers, particularly collagen. • The outside surface of a muscle is covered by a relatively thick and very tough connective tissue, the epimysium, which separates it from surrounding muscles. Arteries and veins run through the endomysium. The collagen fibers of the epimysium are woven into particularly tight bundles that are wavy in appearance. These collagen bundles are connected to the perimysium. The perimysium divides the muscle into bundles MT BIOLOGY
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typically containing about 100 to 150 muscle fibres, which form a fasciculus or fascicle. • The perimysium contains many large collagen bundles that encircle the outer surface of the muscle fibres lying on the outside of a fascicle. • Underneath the thicker perimysial sheets of connective
tissue is a much looser network of collagen fibers that run in various directions and connect with the endomysium. • The endomysium, which is made up of collagen fibers 60 to 120 nm in diameter, surrounds each muscle fiber, again adding more stability.
Location
Structure
Types of muscles • There are three types of muscles as discussed in the table below : Table : Types of muscles fibres Skeletal muscle Smooth muscle • The fibres are long, cylindrical, • These muscle fibres are • unbranched, show alternate light spindle shaped. and dark cross bands under light • Each fibre contains microscope. They are also called a single oval nucleus striped muscle fibres. surrounded by the cytoplasm (sarcoplasm). • Each muscle fibre is an elongated In the cytoplasm the cell surrounded externally myofibrils are arranged by a delicate membrane, the longitudinally. sarcolemma. • These fibres are multi-nucleated • There is no sarcolemma, • or syncytial in nature and cytoplasm however, the fibre is (sarcoplasm) has a large number enclosed by plasma of myofibrils which are tightly membrane. packed.
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These muscles are found in the limbs, These muscles are found body walls, tongue, pharynx and in the posterior part of beginning of oesophagus. oesophagus, stomach, intestine, lungs, urinogenital tract, urinary bladder, blood vessels, iris of eye, dermis of skin and arrector pili muscle of hair. MT BIOLOGY
Cardiac muscle Cardiac muscle is composed of smaller interconnected cells with single nucleus which appear as dark line called intercalated discs. The intercalated discs function as boosters of contraction wave and permit the wave of muscle contraction to be transmitted from one cardiac fibre to another. The myofibrils have transverse faint dark and light bands, which alternate with each other. The fibres have some lateral branches, known as oblique bridges to form a contractile network.
These muscles are found in the wall of the heart and in the wall of large veins (e.g., pulmonary veins and superior vena cava), where these veins enter heart.
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In the presence of calcium ions and These muscles help in They are involved in contraction and energy from ATP, actin and myosin peristalsis which happens in relaxation of heart and large veins. (proteins of muscle fibre) interact tubular viscera. forming actomyosin which causes contraction of muscles.
Features Figure
Function
Nerve supply from central nervous N e r v e s u p p l y f r o m Nerve supply from brain and autonomic system, rapid contraction, soon get autonomic nervous system, nervous system, rapid contraction, never fatigued, voluntary. slow contraction, do not get get fatigued, involuntary. fatigued, involuntary.
Functionally, smooth muscle fibres can be of two types: Single unit smooth muscles : Muscle fibres are –– closely joined together and contract as a single unit. They are found in walls of hollow visceral organs. Multi unit smooth muscles : Muscle fibres –– contract as separate units. They are found in the wall of large blood vessels, arrector pili muscles of skin dermis, ciliary and iris muscles in the eyes.
Neural Tissues • Neural tissue exert the greatest control over the body’s responsiveness to changing conditions. • It generally develops from the ectoderm but microgliocytes (glial cell type) arise from the mesoderm of the embryo.
• The special properties of the cells of the nervous tissue
are, excitability and conductivity. –– Excitability is the ability to initiate nerve impulse in response to stimuli (changes outside and inside the body). –– Conductivity means the ability to transmit a nerve impulse (potential change in membrane of a nerve cell).
Neural tissue consists of nerve cells (neurons) and glial cells I. Neurons • Neurons are structural and functional units of nervous tissue. • Each neuron consists of a cell body or cyton and cell processes, called neurites. Neurites are of two types, • dendrons and axons. MT BIOLOGY
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Table : Types of neurons Based on structure Non-polar neurons
Unipolar neurons
Pseudounipolar neurons
Bipolar neurons
Multipolar neurons
Each neuron has several branched processes (projections). These neurons are rare in vertebrates but occur in cnidarians (coelenterates) e.g., Hydra.
The body has only one axon. It is found usually in the embryonic stage.
A single process arises from the cyton and then divides into axon and dendrite. They are found in dorsal root ganglia of spinal nerves.
Each bipolar neuron has one axon and one dendrite. They are present in the retina of the eye.
These neurons have several dendrites and an axon. They are found in cerebral cortex.
Based on function Afferent (sensory) neuron
Efferent (motor) neuron
Interneuron (relaying neuron)
They connect sense organs with the central nervous system (brain and spinal cord). They bring sensory impulse from sense organs to the central nervous system.
They connect the central nervous system to the effectors (muscles and glands). They carry motor impulses from the central nervous system to the effectors.
They are present in the central nervous system and occur between the sensory and motor neurons for distant transmission of impulses. They are meant for integrating and analysing the input of information and distributing it to other parts of nervous system.
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Nerve fibres • Axon or dendrite of a nerve cell covered with one, two or three sheaths is called nerve fibre. Dendrites
are surrounded only by one sheath. An axon may be surrounded by two or three sheaths.
Table : Types of nerve fibres Based on structure Myelinated (medullated) nerve fibres
Non-myelinated (non-medullated) nerve fibres
The myelinated sheath is composed of substances called myelin which contains lipid, proteins and water. It serves as an insulating layer, preventing loss of energy during impulse transmission. The sheath is continuous around nerve fibres in central nervous system but in peripheral nervous system, it is absent at nodes of Ranvier. Collateral fibres or lateral branches arise from it. They are found in white matter of the brain and spinal cord and in the cranial and spinal nerves where they lack neurilemma.
The non-myelinated fibres lack myelin sheath and are surrounded by neurilemma and connective tissue. There are no nodes of Ranvier and neither collateral fibres. They form grey matter of the brain and spinal cord. These nerve fibres are found in autonomic nerves. Non-medullated fibres conduct nerve impulses much slower than medullated fibres.
Based on function Afferent (sensory) nerve fibres
Efferent (motor) nerve fibres
They carry nerve impulses from the sense organs to the They carry nerve impulses from the central nervous system central nervous system (brain and spinal cord). to the effector organs (muscles and glands). Why speed of nerve impulse conduction is faster in myelinated fibres? Myelin sheath is a protein lipid complex which is wrapped around the axon. Myelin probably serve as a good electrical insulator that prevents the flow of ions between the fluid external to the sheath and the fluid within the axon. Normally, impulse is transmitted along the axon to its termination. Since voltage gated sodium ion channels are highly concentrated at nodes of Ranvier and the initial segment in myelinated neurons, therefore, the action potential can jump large distances from node to node. This process is basically called saltatory conduction of impulse. It is rapid process and myelinated axons conducts upto 50 times faster than the non-myelinated fibres. In no-nmyelinated nerve fibres the ionic flow and depolarisation are repeated along the entire length of the fibre. Therefore impulse conduction is slow in such nerve fibre.
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(ii) Neuroglia or glial cells • Neuroglia or neuroglial cells are specialised cells found in the brain and spinal cord supporting the neurons and their fibres.
• Different types of neurolglial cells are found in
central and peripheral nervous system discussed as following:
Multiple Choice Questions 1. Which one of the following is correct pairing of a body part and the kind of muscle tissue that moves it? (a) Biceps of upper arm – Cardiac muscle fibres (b) Abdominal wall – Striated muscle fibres (c) Iris – Smooth muscle fibres (d) Heart wall – Striated muscle fibres 2. Cartilage is formed by (a) chondrocytes (c) osteoclasts
(b) osteoblasts (d) fibroblasts.
3. Read the following statements and select the correct option. (i) Blood cells secrete fibres of structural proteins called collagen or elastin. (ii) Neuroglial cells protect and support the nephrons. 40
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(iii) Osteocytes are present in spaces called lacunae. (iv) Striated muscle fibres are bundled together in a parallel fashion. (v) Biceps are involuntary and striated. (a) Statements (iii) and (iv) are incorrect (b) Statements (ii) and (iv) are incorrect (c) Statements (i) and (iii) are incorrect (d) Statements (i), (ii), and (v) are incorrect 4. ‘Mummies’ of Egypt still have their arteries preserved due to the presence of (a) yellow elastic connective tissue fibres (b) white fibrous connective tissue fibres (c) cartilage (d) valves.
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5. Match Column-I with Column-II and select the correct option from the codes given below. Column-I Column-II A. Hyaline cartilage (i) Pectoral girdle of frog B. Fibrous cartilage (ii) Long bones, sternum, ribs C. Elastic cartilage (iii) Pubic symphysis D. Calcified cartilage (iv) Eustachian tube, epiglottis (a) A - (i), B - (ii), C - (iii), D - (iv) (b) A - (ii), B - (iii), C - (iv), D - (i) (c) A - (ii), B - (iv), C - (iii), D - (i) (d) A - (iv), B - (iii), C - (ii), D - (i) 6. Which of the following statements is/are not correct regarding connective tissues? (i) Connective tissues are most abundant and widely distributed in the body of complex animals. (ii) They connect and support other tissues. (iii) They include such diverse tissues as bone, cartilage, tendons, adipose and loose connective tissues. (iv) They form the internal and external lining of many organs. (v) In all connective tissues except blood, the cells secrete fibres of structural proteins called collagen or elastin. (a) (iv) only (b) (v) only (c) (i) and (ii) (d) (iii) and (v) 7. Areolar connective tissue joins (a) bones with bones (b) fat body with muscles (c) integument with muscles (d) bones with muscles. 8. Mammalian bone differs from cartilage due to the presence of (a) lymph vessels (b) collagen (c) blood vessels (d) Haversian canals. 9. Bone is connected to muscles with the help of (a) ligament (b) cartilage (c) tendon (d) none of these. 10. The supportive skeletal structures in the human external ears and in the nose tip are examples of (a) ligament (b) areolar tissue (c) bone (d) cartilage.
11. Which one of the following salts predominates in bone matrix? (a) Sodium chloride (b) Magnesium phosphate (c) Calcium phosphate (d) Sodium carbonate 12. Mast cells of connective tissue contain (a) vasopressin and relaxin (b) heparin and histamine (c) heparin and calcitonin (d) serotonin and melanin. 13. S elect the correct statement(s) from the given statements (i-iv). (i) Red bone marrow is active vascular tissue with few fat cells. (ii) Outer circumferential lamellae of matrix of bone occur in endosteum. (iii) White fibrous connective tissue is present at the joints between skull bones. (iv) White fat has a role in non-shivering thermogenesis in new born infants. (a) (iv) only (b) (i) and (iii) (c) (ii) and (iv) (d) (i) only 14. The outer covering of cartilage is called (a) peritonium (b) periosteum (c) endosteum (d) perichondrium. 15. Ground substance of connective tissue is formed of (a) phospholipids (b) lipids (c) monosaccharides (d) mucopolysaccharides. 16. Cartilage is (a) nonvascular (c) highly vascular
(b) poorly vascular (d) irregularly vascular.
17. Which is not the property of yellow fibres? (a) Contain elastin (b) Fewer in number (c) Straight and branched (d) Provide toughness and strength 18. Volkmann’s canal connects (a) osteocyte with matrix (b) different bones (c) Haversian canal with matrix (d) Haversian canal with other Haversian canals. 19. Ligament is a (a) inelastic white fibrous tissue (b) modified white fibrous tissue (c) modified yellow elastic fibrous tissue (d) none of the above. MT BIOLOGY
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20. Study the given figure of T.S. of mammalian bone and select the incorrect option.
26. Cardiac muscle cells differ from striated muscle cells in having (a) a centrally located nucleus (b) different myofibrils (c) fewer mitochondria (d) no sarcoplasmic reticulum. 27. Connective tissue is (a) ectodermal in origin without intercellular spaces (b) mesodermal in origin without intercellular spaces (c) ectodermal in origin with intercellular spaces (d) mesodermal in origin with intercellular spaces.
(a) A : Volkmann’s canal – connects Haversian canals (b) B : Periosteum – present outer to the bone marrow (c) C : Haversian canal – characteristic of mammalian bone (d) D : Sharpey’s fibres – pentrate bone matrix 21. Which of the following statements is correct for node of Ranvier of nerve fibre? (a) Neurilemma is discontinuous (b) Myelin sheath is discontinuous (c) Both neurilemma and myelin sheath are discontinuous (d) Covered by myelin sheath 22. S chwann’s cells are present on which part of a neuron? (a) Dendrites (b) Axon hillock (c) Axon (d) Soma/body. 23. The major constituent of connective tissue is (a) collagen (b) carbohydrate (c) lipid (d) cholesterol. 24. Reticular tissue forms the supporting framework of (a) bone marrow (b) lymph gland (c) spleen (d) all of these. 25. Multilocular adipose tissue differs from unilocular adipose tissue in that it (a) has fewer blood vessels (b) has greater number of mitochondria (c) undergoes lipolysis under influence of epinephrine (d) has cells that are not electrically coupled. 42
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28. Study the diagram given below and identify the cells labelled as A, B, C and D, and select the incorrect statement.
(a) Blood cell A has coarse granules in cytoplasm and takes acidic stain. (b) Blood cell B is motile and phagocytic; often changes into macrophage. (c) Blood cell C engulfs germs and play role in innate immunity. (d) Blood cell D is motile, granular and secretes antibodies. 29. Blood clotting corpuscle is (a) thrombocyte (b) monocyte (c) lymphocyte (d) erythrocyte. 30. Bone resorption is brought about by (a) osteocytes (b) osteoblasts (c) osteoclasts (d) osteoprogenitor cells. answer key 1. (c) 6. (a) 11. (c) 16. (a) 21. (b) 26. (a)
2. 7. 12. 17. 22. 27.
(a) (c) (b) (d) (c) (d)
3. 8. 13. 18. 23. 28.
(d) (d) (b) (d) (a) (d)
4. 9. 14. 19. 24. 29.
(a) (c) (d) (c) (d) (a)
5. 10. 15. 20. 25. 30.
(b) (d) (d) (b) (b) (c) nn
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Growth can be arithmetic (cells divide in such a fashion that one daughter cell divides again while the other cell differentiates) or geometric (each daughter cell divides). Geometric growth causes rapid increase in size, weight, etc. and is generally observed in unicellular organisms or at early embryonic stage.
The content for PMT Biology is very vast. It does not allow students to engage in enquiry so as to develop meaningful knowledge. Essential topic for PMT is presented here to enable students grasp the topic, analyse the kind of questions appearing in PMTs, practice and score HIGH.
DEVELOPMENT Development is the sequence of events that occur in the life history of a cell, organ or organism which in case of angiospermous (flowering), plants include seed germination, growth, differentiation, maturation, flowering, seed formation and senescence. Development involves differentiation, the process by which unspecialised structures become modified and specialised for the performance of specific functions.
GROWTH and DEVELOPMENT IN FLOWERING PLANTS An organism starts its life as a single cell. Unicellular organisms grow and reproduce without increasing number of body cells but multicellular organisms undergo a far more complex process of growth and development.
GROWTH Growth in an organism consists of a permanent and more or less irreversible increase in size, commonly accompanied by an increase in solid matter, dry mass and amount of cytoplasm. Growth in living beings is intrinsic or internal in contrast to extrinsic growth observed in non-living objects. Plant growth is generally indeterminate i.e., continued throughout life. In lower plants, growth is diffused i.e., every cell can divide and enlarge but in higher plants, special body regions called meristems cause body growth. Plant growth takes place in three phases – formative, enlargement and differentiation. (i) Formative phase: It is the phase of cell division. As the formation of new cells requires biosynthetic activity, the respiration rate of cells is high in this phase. (ii) Phase of enlargement: In it, the newly formed cells, produced in formative phase undergo enlargement. In many parts cell enlargement may occur in all directions e.g., isodimetric parenchymatous cells. In many parts, cell enlargement takes place prominently in the linear direction. So much so that this phase is also called phase of cell elongation. (iii) Phase of differentiation or maturation: In this phase the enlarged cells develop into special or particular type of cells by undergoing structural and physiological differentiation.
Growth and development commonly go hand in hand, and are often referred to collectively as morphogenesis. MT BIOLOGY
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‘Nature vs. Nurture’ in growth and development The processes of growth and development are influenced by many factors, some internal to the organism and some environmental or external. From observation of living things it may be difficult to determine whether a particular feature of growth such as body height is determined largely by internal factors, namely the inherited instructions each organism receives in its genes, or by some environmental factor such as the food supply available to the organism. This is because the effects of internal and external factors interact. The interaction of internal and external factors in growth and development are sometimes referred to in literature as ‘nature vs. nurture’. The distinction is one of ‘genetic vs. environmental’ influences. The whole process of interaction of factors and the expression of characters can be summarised as:
Germination and growth of embryo A typical angiospermic seed consists of seed coat, embryo and endosperm. Seed may be defined as the fertilized
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integumented megasporangium. Germination is the onset of growth of the embryo, usually after a period of dormancy. Seed germination produces a seedling that grows into a new plant. Several external and internal conditions affect seed germination.
Seed dormancy Dormancy is inactive state of the seed in which growth of embryo is temporarily suspended for a specific length of time. Dormancy may be relative (due to genes) which is a must for any seed and cannot be removed by any method or compulsory or forced dormancy caused due to non-availability of favourable conditions which can be removed by providing favourable conditions. Dormancy allows storage of seeds for later use.
Necessary conditions for germination Water uptake Germination can commence after the uptake of water by the seed. Water is absorbed by imbibition through the
micropyle and the testa. The resultant swelling of the seed may rupture the testa. Subsequent movement of water in the hydrated seed tissue is by osmosis. Water is essential for vacuolation of growing cells, for activation of enzymes, for hydrolysis of stored substances and for translocation of hydrolysed food reserves to the site of growth of embryo.
enzymes. GA is formed by the embryo only after sufficient water has been absorbed. Mobilisation of food reserves in linked to germination. Seed germination is a complex process summarised in the following flowchart.
Temperature The optimum temperature for germination refers to the temperature required for the activity of enzymes involved in mobilisation of food reserves, provided that other factors are non-limiting. The temperature varies from species to species. Oxygen Respiration makes available the energy for metabolism and growth. Germinating seeds respire very rapidly, and require oxygen for aerobic respiration. Seeds will not germinate in the total absence of oxygen. Diffusion of oxygen through the testa may be slow, however, and in the early stages of germination seeds may relay on some anaerobic respiration, at least until the testa has ruptured. Mobilisation of stored food The stored food of seeds consist of carbohydrates, lipids and proteins. Stored food is hydrolysed to produce the substrates for respiration (sugars) and the building blocks for synthesis (substances such as sugars, amino acids and fatty acids). Release of hydrolytic enzymes is triggered by gibberellic acid, which is produced in the embryo and diffuses to the food store. GA works directly on the nuclei of the food storage cells, activating the genes that code for hydrolytic
Types of seed germination The two main types of germination in plants are epigeal and hypogeal germination. • In epigeal germination, the cotyledons are carried up and out of the soil by the growth of the hypocotyl e.g., castor, bean.
• In hypogeal germination, the cotyledons remain below ground because hypocotyl does not elongate. e.g., cereals millets, coconut, etc.
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their origin, meristems are of two types: primary and secondary. Primary meristems are those meristematic tissues which are derived directly from the meristems of the embryo. They are divided into apical meristems, intercalary meristems and lateral meristems depending upon their position in body. Apical meristems are of two types: root apical meristem present on root apex and shoot apical meristem present on shoot apex. Root apical meristem (RAM) and shoot apical meristem (SAM) contribute cells for elongation of plant parallel to its axis. It is primary growth. Another meristem contributing to primary growth is intercalary meristem located above the nodes in grasses and related plants. It increases length of the plant organs.
Vivipary Several species of mangrove plants show extraordinary phenomenon of vivipary, i.e., germination of seeds inside the fruit while it is still attached to the parent tree. Thus, the embryo is attached and nourished by the parent plant, grows into a more or less developed plant without undergoing any rest period, e.g., in Rhizophora, Breiquira and Cereops. In these plants, embryo grows not only out of the seed but also out of the fruit and projects from the latter in the form of a green seedling displaying root and hypocotyl. The cotyledons serve as a haustorium (sucking food from the parent plant). Finally the seedling breaks loose from the cotyledons, which remains inside the fruit and shrivel with it. The seedling falls into mud or water, its club-shaped and pointed root end pierces into mud where it rapidly thrusts and soon develops lateral roots. In plants, the growth of embryo occurs by cell division, enlargement and differentiation. The first visible sign of growth in a plant embryo is the emergence of radicle (embryo root) and plumule (embryo shoot). Embryo after germination forms leaves, and other organs. These organs are produced by embryonic meristematic cells called promeristem, primordial meristem or embryonic meristem.
Role of meristems in plant growth Meristems are the region of growth in plants. Cells of the meristematic region have the capacity to divide and self perpetuate. They produce cells which lose the capacity to divide and enter G0 phase for undergoing differentiation to form particular tissues and organs. Depending on 48
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The meristem which is consumed in the formation of an organ is called determinate meristem. The meristem which continues its activity throughout life of the plant is called indeterminate meristem.
Lateral meristems contribute tissues for growth in girth. Only one type of primary lateral meristem is found in plants i.e., intrafascicular cambium. Lateral meristems also include secondary meristems which cause secondary growth of plant. Secondary meristems are formed secondarily from the permanent tissues as some of the permanent cells acquire the power of division. This phenomenon is called dedifferentiation. The secondary meristems are usually lateral. They are cylindrical meristems. They give rise to secondary tissues e.g., vascular cambium of the root, interfascicular vascular cambium of stem, cork
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cambium or phellogen (from an outer layer of cortex), wound cambium (from the cells surrounding an area of injury or wound) and accessory cambia of monocots.
Primary growth and development Primary growth is the first form of growth to occur. A whole plant can be built up by primary growth, and in most monocotyledonous plants and herbaceous dicotyledons it is the only type of growth. It is a result of the activity of the apical, and sometimes intercalary meristems. The seedling undergoes primary growth to form the herbaceous (non-woody) green plant. Primary growth is initiated by divisions of meristematic cells at the apex of stem and root, the apical meristems. Growth and development of shoot The shoot is composed of two organs : the stem and leaves. The primary growth of the shoot is concentrated at the shoot tip. All tissues of the stem and leaves arise from terminal meristem. Leave primordia originate on the lateral flanks of the apical meristem. Shoot apical meristem and the young primordia is commonly termed the bud. The leaf primordia subsequently grow and differentiate into leaves and lateral buds. The point of attachment of the leaf and lateral bud on the stem is the node. The stem between the nodes is referred to as the internode. Growth of the stem axis is by cell enlargement in the internodal region caused by intercalary meristem. There is a progressive increase in the distance between the young nodes and the apex of the shoot is pushed upward. Branch primordia develop in the axil of old leaves. The primary meristem forms dermatogen, periblem and plerome (Hanstein’s histogen theory). Dermatogen forms epidermis, periblem forms cortex and plerome forms stele the part inner to endodermis. Central part of plerome which forms vascular tissues is called procambium. Stem consists of vascular tissue in the centre. During the formation of vascular tissue, the innermost cells of the procambial strands of the stem form the protoxylem. Cells at the outer side of the procambial strands form the protophloem. Metaxylem and metaphloem tissues are formed subsequently. Cells of the procambial strand may 50
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also differentiate into fibres, a form of sclerenchyma. The formation and enlargement of more robust metaxylem and metaphloem tends to crush the first-formed vascular tissue, particularly the protophloem. The differentiation of phloem involves the formation of phloem sieve tubes and accompanying companion cells.
Growth and development of root The apical meristem of the root is a mass of irregularly arranged cells, which divide and cut off new cells in all directions. The cells which cut off ahead of this meristem form the root cap. In monocots and many other plants, calyptrogen forms root cap. Dermatogen, periblem and plerome form the root tissues in a fashion similar to stem development. The bulk of the cells cut off by the root apical meristem gives rise to the central procambial strand, and to the tissues of the cortex. Protoxylem and protophloem develop from the procambial strand cells followed by metaxylem and metaphloem. The central vascular tissue is referred to as the stele. The stele is surrounded by a single layer of cells, the endodermis, and immediately within this layer is a layer of cells, the pericycle. Development of cambium in dicot plants After primary growth is completed and the mature primary tissues of stem and root are formed, some procambial strand cells remain in the vascular bundles of the stem and in the stele of the root. These meristematic cells lie between the metaxylem and metaphloem, and are known as cambium. Cambium cells are capable of further growth, leading to secondary growth of roots and stems. The developmental phase in plant life when rapid primary growth occurs is called juvenile phase. This phase begins with young seedling and continues until the plant begins reproductive development. In some plants, juvenile phase extends for a long period, sometimes indefinite, e.g., English ivy. Juvenile phase is followed by maturity. At maturity plant shows reduced vegetative growth and active reproductive growth.
At maturity : Flowers and fruits develop in monocarpic plants (flower once in their life) and they die after flowering and fruiting, while eucarpic plants resume vegetative growth again after flowering and fruiting. In dicots of angiosperms and gymnosperms, the primary body forms the fundamental structure and increase in girth and diameter takes place by the formation of secondary tissue. This formation of secondary tissue is called secondary growth.
Secondary growth and development Secondary growth is the growth in thickness due to the formation of secondary tissues by lateral meristems. With the exception of some annuals, most of the dicots and gymnosperms show secondary growth in their roots. It takes place by the production of two types of secondary tissues. They are secondary vascular tissues and periderm. These tissues are formed by meristems, vascular cambium and cork cambium respectively. Secondary growth results in the formation of a large amount of secondary xylem called wood and of external cork layer known as bark.
from phloem strands to form a complete ring of cambium. Thus, a continuous wavy ring is produced which is present below the phloem but above the xylem and is secondary in origin. Soon, the cambium becomes circular by its divisions and secondary tissue formation. Some cambial cells may function as ray initials and produce secondary medullary rays. Secondary vascular tissue assumes the shape of continuous cylinder interrupted at places where wide vascular ray connect primary xylem to cortex through pericycle and endodermis. The primary xylem remains in its original position but the primary phloem is pushed towards outerside and crushed.
Secondary growth in dicot roots Secondary growth in dicotyledonous roots occurs by the initiation and activity of two secondary meristems– (i) vascular cambium and (ii) cork cambium (or phellogen). Stelar growth by vascular cambium The process of stelar secondary growth in dicotyledonous roots begins with the initiation of vascular cambium strips which develop from the parenchymatous cells present along the inner edges of primary phloem. The number of cambial strips depends on the number of phloem or xylem strands. The cells of cambium strips (vascular cambium) divide repeatedly to produce new cells both towards inner as well as outer side. The cells produced towards innerside (centripetally) differentiate into secondary xylem elements and those produced towards outerside (centrifugally) differentiate into secondary phloem. Subsequently, the cells of pericycle lying towards outer side of protoxylem divide by tangential division. The inner derivatives of these cells become meristematic and function as cambium. These join with cambia derived
Extrastelar growth by cork cambium Addition of more and more tissues of secondary xylem and secondary phloem in the central part of root exerts pressure towards periphery. The tissues outside this zone of active growth get crushed and are sloughed off. To avoid injury of secondary phloem, the roots develop a new cambium ring in the pericycle, called cork cambium (phellogen). The cells of cork cambium (phellogen) divide to form cells of cork (phellem) towards outer side and secondary cortex MT BIOLOGY
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(phelloderm) towards inner side. It results in the formation of outer protective covering consisting of multilayered cork, cork cambium and multilayered secondary cortex. These three layers make the periderm.
Secondary growth in dicot stems Stelar growth by vascular cambium The dicotylcdonous stems are characterized by presence of fascicular cambium (primary meristem) derived from procambium of shoot apical meristem between xylem and phloem. The parenchymatous cells beside the fascicular cambium become meristematic and develop a new cambium, called interfascicular cambium (secondary meristem). The cambium ring formed by joining of fascicular and interfascicular cambium, is called vascular cambium. It is composed of two types of cells– the fusiform initials and the ray initials. The cells of cambium mostly divide by periclinal divisions. Out of the two cells produced from single cell of cambium, one differentiates into secondary tissue and the other remains cambial cell. In this way the cambial cells, by repeated divisions, add new cells either towards centre or towards periphery and the cambium still remains single layered. Formation of secondary xylem and secondary phloem The fusiform initials of cambium ring divide by tangential divisions and add new cells. The new cells produced toward inner side (i.e., towards primary xylem) may remain meristematic for sometime and differentiate into elements of secondary xylem. On the other hand, the new cells produced towards outer side (i.e., towards primary phloem) remain meristematic for a limited period and differentiate into secondary phloem. The primary phloem gets crushed. Formation of secondary medullary rays Ray initials of intrafascicular vascular cambium divide by tangential division and add new cells which form secondary medullary rays. They are usually one to few layers in thickness and one to several layers in height. The medullary rays form the radial system responsible for radial conduction of solutes. They maintain connection between pith and cortex. 52
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Annual rings Annual ring (growth ring) is the wood formed in a single year. It consists of two types of wood, spring wood and autumn wood. The spring or early wood is much wider than the autumn or late wood. It is lighter in colour and of lower density. Spring wood consists of larger and wider xylem elements. The autumn or late wood is dark coloured and of higher density. The transition from spring to autumn wood in an annual ring is gradual but the transition from autumn wood to the spring wood of the next year is sudden. Therefore, each year’s growth is quite distinct. The number of annual rings corresponds to the age of the plant, the annual rings also give some clue about the climatic conditions of the past through which the plant has passed. Dendrochronology is the science of counting and analysing annual growth rings of trees.
Sapwood and heartwood The wood of the older stems (Dalbergia, Acacia) formed by secondary growth gets differentiated into two zones, the outer light coloured and functional sapwood or alburnum and the inner darker and nonfunctional heartwood or duramen.
Table : Difference between sapwood or alburnum and heartwood or duramen Sapwood (Alburnum) Heartwood (Duramen) 1. It is outer wood of an It is the central wood of an old stem. old stem. 2. It is light coloured.
Heartwood coloured.
is
dark
3. Living cells are present.
Living cells are absent.
other than harmful external conditions, which are clearly degenerative ultimately irreversible. Senescence may be overall (whole plant dies), top (only aerial organs die), deciduous (annual leaf senescence, and progressive (senescence of organs continues throughout the year). Genetic factors, toxic substances, environmental factors and wear and tear of organs may lead to senescence followed by death.
4. Sapwood is the Heartwood is the functional part of the nonfunctional part of secondary xylem or secondary xylem. wood. 5. The tracherary elements The tracheary elements are not plugged by are plugged by tyloses. tyloses. 6. Tracheary elements Tracheary elements have do not possess any deposition of tannins, deposition in their resins, gums, etc. lumen. 7. Sapwood or albunum is Heartwood is heavier. lighter. 8. It is less durable because it is susceptible to attack by pathogens and insects.
It is more durable due to its little susceptibility to the attack of pathogens and insects.
Anomalous secondary growth It is abnormal type of secondary growth that occurs in some arborescent monocots (e.g., Dracaena, Yucca, Agave) and storage roots (e.g., beet, sweet potato). In arborescent monocot stems, a secondary cambium grows in hypodermal region. The latter forms conjunctive tissue and patches of meristematic cells. The meristematic patches grow into secondary vascular bundles. Amomalous vascular bundles also occur in cortex (cortical bundles, e.g., Nyctanthes) and pith (e.g., Boerhaavia). In storage roots (e.g., beet), accessory cambial rings appear in the outside of endodermis. They produce less secondary xylem but more secondary phloem. The secondary phloem contains abundant storage parenchyma.
SENESCENCE AND DEATH Senescence is a collective term for the processes accompanying aging that lead to death of a plant or plant part. It is the last phase in development of a plant. Senescence can be defined as changes caused by factors
Death is the last event in developmental process. NEW MCQs 1. In dicot roots cork cambium originates in (a) pith (b) hypodermis (c) pericycle (d) endodermis. 2. Differential division of RAM gives rise to (a) protoderm (b) procambium (c) calyptrogen (d) all of these. 3. Which of the following is a primary lateral meristem? (a) Interfascicular cambium (b) Intrafascicular cambium (c) Cork cambium (d) Phellogen. 4. During secondary growth in dicot root phellogen form _____ towards outerside. (a) periderm (b) secondary vascular tissue (c) cork cambium (d) phellem. 5. Spring wood is _____ than autum wood, ____ in colour and _____ in density. (a) wider, lighter, lower (b) narrower, lighter, lower (c) wider, dark, higher (d) narrower, dark, higher. 6. Growth is a (a) reversible increase in size (b) reversible increase in shape (c) irreversible increase in size (d) none of the above. MT BIOLOGY
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7. Meristem which is consumed in the formation of organ is (a) determinate meristem (b) indeterminate meristem (c) secondary meristem (d) lateral meristem. 8. Cells enter _______ phase for undergoing differentiation. (a) G1 (c) G0
(b) S (d) G2.
9. Cell enlargement may occur in (a) all directions (b) linear direction (c) both (a) and (b) (d) none of these. 10. Sap wood is (a) outer wood of an old stem (b) central wood of an old stem (c) non functional part of secondary stem (d) heavier. EXAM SECTION 1. As a tree grows older, which of the following increases more rapidly in thickness? (a) Heart wood (b) Sap wood (c) Phloem (d) Cortex. (CBSE-PMT 1994) 2. Cork cambium and vascular cambium are the examples of (a) apical meristem (b) lateral meristem (c) wound tissue (d) intercalary meristem. (DPMT 1991, 1995; CMC Vellore 2013 ) 3. Procambium is situated just behind apical meristem. Procambium gives rise to (a) vascular cambium (b) primary vascular bundle (c) cork cambium (d) both (a) and (c). (DPMT 1993, 2001) 4. Vascular cambium in roots takes its origin from (a) pericycle (b) conjunctive parenchyma (c) both (a) and (b) (d) none of these (DPMT 2004, 2006) 5. Secondary growth in dicot stem is the activity of (a) xylem (b) cork cambium (c) vascular cambium (d) both (b) and (c). (Manipal 1995) 6. Annual rings are distinct in plants, which grow in (a) tropical regions (b) grass land (c) temperate region (d) arctic regions. (Manipal 1999) 54
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7. Which of the following is not a character of meristematic tissue? (a) Presence of prominent nucleus (b) Intercellular space present (c) Absence of vacuole (d) Proplastid present. (Manipal 2004) 8. Growth in numbers is maximum in the zone of (a) cell maturation (b) cell division (c) cell elongation (d) all of these. (AFMC 1994) 9. When seed germinates, while the fruit is attached to the parent plant, it is called (a) parthenocarpy (b) vivipary (c) apomixis (d) parthenogenesis (BHU 1996) 10. Which of the following four phases, in the post emergence life of an angiospermic plant, begins just after germination of seed and ends when the plant develops the capacity to reproduce? (a) Death (b) Maturity (c) Ageing (d) Juvenility (DPMT 1998) 11. Vascular tissues in flowering plants develop from (a) periblem (b) dermatogen (c) phellogen (d) plerome. (CBSE– PMT 2008) 12. Anatomically fairly old dicotyledonous root is distinguished from the dicotyledonous stem by (a) absence of secondary phloem (b) presence of cortex (c) position of protoxylem (d) absence of secondary xylem (CBSE– PMT 2009) 13. Heartwood differs from sapwood in (a) presence of rays and fibres (b) absence of vessels and parenchyma (c) having dead and non-conducting elements (d) being susceptible to pests and pathogens.
(AIPMT Prelims 2010)
14. Which one of the following pairs is an example for lateral meristem? (a) Procambium and phelloderm (b) Interfascicular cambium and phellem (c) Phellogen and phelloderm (d) Phellogen and fascicular cambium. (Karnataka 2010)
15. Youngest layer of secondary xylem in wood of dicot plants is located between (a) pith and primary xylem (b) just outside vascular cambium (c) just inside vascular cambium (d) just inside cork cambium. (Kerala 2000) 16. Secondary growth of dicot stem is due to (a) phelloderm (b) bark (c) lateral meristem (d) wood cork. (Manipal 2000) 17. Root cap is formed by (a) dermatogen (b) calyptrogen (c) vascular cambium (d) wound cambium. (AIIMS 2000) 18. The apical meristem of the root is present (a) only in radicals (b) only in tap roots (c) only in adventitious roots (d) in all the roots (CBSE– PMT 2003) 19. Between the bark and the wood in a woody stem, there is a layer of meristem called (a) cork cambium (b) apical meristem (c) vascular cambium (d) the zone of cell division (Manipal 2006)
25. Which one of the following is not correct? (a) Early wood is characterized by large number of xylary elements (b) Early wood is characterized by vessels with wider cavities (c) Late wood is characterized by large number of xylary elements (d) Late wood is characterized by vessels with narrower cavities. (AMU 2010) ASSERTION AND REASON The following questions consist of two statements each : assertion (A) and reason (R). To answer these questions, mark the correct alternative as directed below : (a) If both A and R are true and R is the correct explanation of A. (b) If both A and R are true but R is not the correct explanation of A. (c) If A is true but R is false. (d) If both A and R are false. 1. Assertion (A) : Vascular cambium is single layered but
20. The secondary meristem initiates (a) basal growth (b) transverse growth (c) radial growth (d) vertical growth (J & K 2007)
21. Intercalary meristem occurs at the (a) bases of internodes of monocot plants (b) buds of the axillary leaves (c) apex of dicot stem (d) between the phloem and xylem (J & K 1998)
22. Secondary cortex is also known as (a) phellem (b) phelloderm (c) phellogen (d) bark. (Karnataka 2012) 23. The cork cambium, cork and secondary cortex are collectively called (a) phelloderm (b) phellogen (c) periderm (d) phellem (AIPMT Prelims 2011) 24. Which one of the following is not a lateral meristem? (a) Intrafascicular cambium (b) Interfascicular cambium (c) Phellogen (d) Intercalary meristem. (AIPMT Prelims 2010)
appears to be 2-3 layer in thickness due to presence of immediate derivatives. Reason (R) : Cells of vascular cambium divide by unipolar division to form secondary permanent tissue.
2. Assertion (A) : Cells of the meristematic region enter
G0 phase. Reason (R) : Cells of meristem undergo differentiation to form a particular tissue or organ.
3. Assertion (A) : Germinating seeds respire slowly. Reason (R) : Germinating seeds require only anaerobic
environment for initiations of germination. 4. Assertion (A) : Intercalary meristem helps in
elongation of the organs. Reason (R) : Intercalary meristematic regions are derived from the apical meristem.
5. Assertion (A) : Abnormal type of secondary growth
occur in some arborescent monocots. Reason (R) : In arborescent monocot stems, secondary cambium grows in hypodermal region. SHORT ANSWER TYPE QUESTIONS
1. Fill in the blanks. (a) Water is essential for _______ of the growing cells. MT BIOLOGY
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(b) Pith cells are living cells, with little _______ and _______ in their walls. (c) Lateral meristems involved in secondary growth of a plant are _______ and _______. (d) Strain at the circumference of the stem resulting from secondary thickening causes epidermis to _______. 2. Summarise the effect of abiotic factors on germination. 3. Differentiate between heart and sap wood. 4. Describe the role of two meristems involved in secondary growth of dicot root. ANSWERS Part - I 1. (c) 6. (c)
2. (d) 7. (a)
3. (b) 8. (c)
4. (d) 9. (a)
5. (a) 10. (a)
Part - II 1. (a) 6. (c) 11. (d) 16. (c) 21. (a)
2. (b) 7. (b) 12. (c) 17. (a) 22. (b)
3. (b) 8. (b) 13. (c) 18. (d) 23. (c)
4. (c) 9. (b) 14. (d) 19. (c) 24. (d)
5. (d) 10. (d) 15. (c) 20. (c) 25. (c)
2. (d)
3. (d)
4. (b)
5. (a)
Part - III 1. (c) Part - IV 1. (a) vacuolation (b) thickening, no lignification (c) vascular cambium, cork cambium (d) split 2. Necessary abiotic factors for germination are water, temperature and oxygen. Seed imbibes water and the resultant swelling may rupture the seed coat. Water is also essential for vacuolation of the growing cells for activation of enzymes, hydrolysis of stored substances and translocation of hydrolysis of food reserve to the site of growth of embryo. Optium temperature is necessary to enzymatic activity and energy for metabolism and growth comes through respiration. 3. Differences between sapwood or alburnum and heartwood or duramen are summarised in the given table. 56
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Sapwood (Albumum)
Heartwood (Duramen)
1. It is outer wood of an old It is the central wood of stem. an old stem. 2. It is light coloured.
Heartwood coloured.
is
dark
3. Living cells are present.
Living cells are absent.
4. Sapwood is the functional Heartwood is the part of the secondary nonfunctional part of xylem or wood. secondary xylem. 5. The tracherary elements The tracheary elements are not plugged by tyloses. are plugged by tyloses. 6. Tracheary elements do not Tracheary elements have possess any deposition in deposition of tannins, their lumen. resins, gums, etc. 7. Sapwood or albunum is Heartwood is heavier. lighter. 8. It is less durable because it It is more durable due to is susceptible to attack by its little susceptibility to pathogens and insects. the attack of pathogens and insects. 4. Secondary growth in dicotyledonous roots occurs by the initiation and activity of two secondary meristems– (i) vascular cambium and (ii) cork cambium (or phellogen). Vascular cambium derives from dedifferentiation of cells inner to primary phloem and pericycle cells outer to protoxylem. The cells of cambium strips (vascular cambium) divide repeatedly to produce new cells both towards inner as well as outer side. The cells produced towards innerside (centripetally) differentiate into secondary xylem elements and those produced towards outerside (centrifugally) differentiate into secondary phloem. Multiseriate vascular rays are also produced from vascular cambium derived from pericycle cells i.e., ray initials. The primary xylem remains in its original position but the primary phloem is pushed towards outerside and crushed. Cork cambium derives from dedifferentiation of pericycle cells. The cells of cork cambium (phellogen) divide to form cells of cork (phellem) towards outer side and secondary cortex (phelloderm) towards inner side. It results in the formation of outer protective covering consisting of multilayered cork, cork cambium and multilayered secondary cortex. These three layers make the periderm. nn
●●
●●
The acronym “GERL” stands for Golgi - Endoplasmic Reticulum - Lysosomal complex. It is a saccular structure that is rich in acid phosphatase, associated with the trans or maturing face of the Golgi complex. These three organelles form a system that combines with the endocytotic and exocytotic pathways to provide a mean by which the cell : –– Processes and packages secretory material in endo and exocrine cells. –– Ingests or endocytoses external substances via phagocytosis and pinocytosis and excretes or exocytoses internal substances. –– Performs many developmental processes involving shedding or remodeling of tissues, with removal of whole cells and extracellular material. For
example, the degeneration of the tadpole tail is caused by the action of cathepsins (i.e., proteolytic enzymes) contained in the lysosomes.
CONSTITUENTS OF GERL SYSTEM Golgi apparatus (Golgi complex) ●● Golgi complex was named after Camillo Golgi who recognised the organelle in nerve cells of barn owl (in 1898). It is present in eukaryotic cells, except in mature sieve tubes of plants, mature RBCs of mammals, sperm cells of bryophytes and pteridophytes, etc. ●● It is absent in prokaryotic cells. In plants, it is called dictyosome (cisternae not interconnected). ●● It is surrounded by a zone of cytoplasm which is devoid of organelles. It is called zone of exclusion. MT BIOLOGY
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Ultrastructure ●● Golgi complex is in the form of a parallely arranged interconnecting system of a cluster of smooth membranes having a central stack of flattened sacs or cisternae (size : 0.5 mm to 1.0 mm diameter). These membranes lack bound ribosomes. ●● It has a complex network of tubules and vesicles and
●●
These appear in the form of flat, curved, smooth membraned structures with swollen ends. They have a definite polarity. Their convex pole or proximal pole or cis face is associated with nuclear envelope. The concave pole or distal pole or trans face, is the oldest, which gives rise to the secretory vesicles.
(i)
Cisternae or Saccules
(ii)
Tubules
These are small, flat, interconnecting structures arising from the periphery of cisternae due to fenestrations of the cisternae.
(iii)
Vesicles
These are large rounded sacs present at the edges of cisternae in clusters. These are pinched off from the tubules. These are of two types: (i) Smooth vesicles : These are smooth surfaced secretory vesicles and contain secretory granules. (ii) Coated vesicles : These are rough surfaced, spherical protuberances arising from the tubules of cisternae.
(iv)
Golgian vacuoles
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is present around or above the centriole in animal cells and scattered in cytoplasmic matrix in plant cells. The stack of cisternae has a definite polarity because there are two distinct faces i.e., forming face (cis region) and a maturing face (trans region), that are different from one another. There are four parts of Golgi complex:
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These are large, spherical vacuoles produced at maturing face. These are filled with some granular
or amorphous substances. Some of them function as lysosomes.
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Functions ●● The principal function of Golgi apparatus is processing, packaging, transport and release of secretory proteins. ●● It produces secretion granules i.e., membrane enclosed complexes, which store hormones and enzymes in protein secreting cells. ●● Site of formation of lysosomes i.e., large irregular structures surrounded by membrane which are present in the cytoplasm. ●● The Golgi complex plays a major role in the glycosidation of lipids and proteins to produce glycosphingolipids and glycoproteins. The carbohydrate prosthetic groups of both these complex substances are added in a sequential manner in the Golgi complex by the action of the various glycosyl transferases. ●● Golgi apparatus helps in the recycling of broken plasma membrane during endocytosis.
Endoplasmic reticulum (ER) ●● The endoplasmic reticulum was first noticed independently by Porter (1945) and Thompson (1945). It was named ER by Porter (1953). ●● The cytoplasm in eukaryotic cells is traversed by a complex network of inter-connecting membrane bound structures. They divide intracellular space in two compartments, i.e., luminal (inside ER) and extra luminal (cytoplasm). These can extend from nuclear envelope to plasma membrane. ●● ER is a complex series of tubules whose walls are made up of unit membrane. Through this network of tubules, substances may be delivered from the outer membrane of cell proper to the membrane of the nucleus or to other inclusion bodies of the cells e.g., mitochondria. Ultrastructure ●● The endoplasmic reticulum is composed of three kinds of structures: They are long, flattened, parallel, saclike, interconnected structures. These Cisternae are found in cells which are actively involved in protein synthesis. The cisternae usually occur in those cells which have synthetic roles, e.g., cells of pancreas and brain. Tubules They are branched or unbranched structures forming the reticular system alongwith the cisternae and vesicles. They are the common in cells involved in lipid and sterol synthesis. Vesicles They are oval, membrane bound vacuolar structures. They are abundant in the pancreatic cells and these are only ER structures found in spermatocytes.
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Sarcoplasmic reticulum The sarcoplasmic reticulum (SR) is an amplified form of SER formed by wide anastomosing tubules having a preferential longitudinal disposition. These tubules cover the surface of the sarcomere at the level of the A-and I-bands and terminate on the Z-discs by special terminal cisternae. These are called as transverse tubules (or T Tubules). The major difference between the functions of sarcoplasmic reticulum is, unlike SER, SR is involved in stimulation and release of Ca++ from the terminal cisternae. T tubule lies adjacent to the ends of longitudinal sarcoplasmic reticulum tubules that surround all sides of the actual myofibrils. The action potential of the T tubules causes current flow into the sarcoplasmic reticular cisternae causing rapid opening of large numbers of calcium channels through the membranes of the cisternae as well as their attached longitudinal tubules. These channels remain open for a few milliseconds; during this time, enough calcium ions are released into the sarcoplasm surrounding the myofibrils to cause contraction.
Functions of endoplasmic reticulum Common functions of smooth and rough ER (i) They function as cytoskeleton and provide mechanical support to colloidal protoplasm. 60
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(ii) They act as a medium of intracellular transport and exchange of materials. (iii) They keep the cell organelles properly distributed in relation to one another.
(iv) They give membranes to Golgi apparatus for the formation of vesicles and lysosomes. (v) They help in formation of desmotubules which extend through the plasmodesmata.
Functions of RER (i) It provides surface for protein synthesis. (ii) It contains SRP receptors or ribophorins for providing attachment to ribosomes. RER provides a large surface area to ribosomes. (iii) The proteins in ER lumen are processed and are packed in membrane bound vesicles for storage or export, or further processing in Golgi apparatus. (iv) Formation of nuclear envelope and plasma membrane. (v) Smooth ER formation by discarding ribosomes. (vi) It provides enzyme precursors for the formation of lysosomes by Golgi complex. Functions of SER (i) Fat and steroidal hormone synthesis. (ii) Glycogen metabolism. (iii) Detoxification of drugs/xenobiotics using cytochrome P450. (iv) Muscle contraction by release and uptake of Ca++ (sacroplasmic reticulum). (v) Formation of organelles like-sphaerosomes and glyoxysomes.
Signal recognition particle The signal recognition particle (SRP) is a ribonucleoprotein complex in which the RNA and protein components are highly conserved across all kingdoms of life. Responsible for directing protein traffic within a cell, and then allowing proteins to be secreted from the cell, the SRP plays an integral role in the process of co-translational protein targeting. A ribosome, an organelle that produces proteins, forms a complex with the protein it is synthesizing, or translating. This ribosome-nascent chain complex (RNC) binds the SRP, delaying protein translation until the ribosome-bound SRP reaches the SRP receptor in the membrane of a eukaryotic cell’s endoplasmic reticulum, or a prokaryote’s plasma membrane. The cleavage of two guanosine triphosphate (GTP) molecules then occurs without interference or help from any external activation factors. This action is coupled to the final step of this process, wherein the SRP is released from its receptor and from the RNC, allowing translation to resume while the protein sequence moves through the translocation channel. Cytochrome P450 The elimination of foreign compounds (xenobiotics) such as drugs and toxins from the body is called as detoxification, which is an essential process to protect against potential toxicity from the foods we eat. The food broken down in stomach is absorbed by the small intestine and then ferried directly to the liver portal vein. This allows the liver to detoxify compounds before they are distributed by circulatory system. Cytochrome P450 (CYP) enzymes are a superfamily of mono-oxygenases that are found in all kingdoms of life. In mammals, these enzymes are found primarily in the membranes of the endoplasmic reticulum within liver cells (hepatocytes), as well as many other cell types. These enzymes use haem iron to oxidise molecules, often making them more water-soluble for clearance. They achieve this by either adding or unmasking a polar group. CYP enzymes are responsible for the oxidative metabolism of a wide number of compounds and are the major enzymes involved in drug metabolism.
Lysosome ●● Christian de Duve first observed these organelles in animal cells in 1949, by cell fractionation studies and Novikoff (1960) suggested that they are derived from pinocytic vesicles. MT BIOLOGY
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These are single membrane bound small vesicular structures of 0.2 – 0.5 mm in diameter or larger, rich in hydrolyzing enzymes (acid hydrolases). One important property of lysosomes is their stability in the living cell. The enzymes are enclosed by a membrane and are not readily available to the substrate. This socalled latency of the lysosomal enzymes is due to the presence of the membrane. The membrane is resistant to the enzymes that it encloses, and the entire process of digestion is carried out within the lysosome. In this way, it protects the rest of the cell from the destructive effect of the enzymes, and its stability is of fundamental importance to the normal function of the cell.
Ultrastructure ●● Each lysosome is a small vesicle surrounded by a single membrane and contains about 50 strong hydrolytic enzymes (acid hydrolases), which are capable of digesting or breaking down all powerful biological substances. ●● Hydrolytic enzymes of lysosomes act at an acidic pH. The acidic condition is maintained by pumping protons into the interior of lysosomes. Some of the hydrolytic enzymes are acid phosphatases, acid ribonucleases,
acid deoxyribonucleases, cathepsins, glycosidases, etc.
●●
●●
●●
Lysosomal membrane is generally strengthened by cholesterol, cortisone, heparin etc. They are called membrane stabilizers. Excess of liposoluble vitamins, steroidal sex hormones, bile salts, X-rays and UV rays make the lysosomal membrane fragile. They are called membrane destabilizers. The organelle shows polymorphism. According to the current interpretation, the polymorphism is the result of the association of primary lysosomes with the different materials that are phagocytized by the cell. On the basis of morphology, their contents and functions, lysosomes are divided into following four forms:
(i) Primary lysosomes (ii) Secondary lysosomes
These are also called heterophagosomes or disgestive vacuoles, which are formed when phagosomes fuse with already existing primary lysosomes. These contain the enzymes against the material to be digested. These are formed from digestive and autophagic vacuoles which contain only undigested materials. Residual bodies pass outwardly, come in contact with plasmalemma and throw their contents to the outside through ephagy or exocytosis.
(iv) Autophagic vacuoles
These are small, vesicle-like newly formed structures produced from the Golgi apparatus, at trans face. Primary lysosomes contain inactive enzymes.
(iii) Residual bodies
Table: Polymorphism in lysosome
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They are formed by union of many primary lysosomes around old or dead organelles, surround them with vacuolar membrane and digest them by autolysis or autodigestion.
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Vesicular transport processes or transcytosis Many substances are transported across the cell membrane by endocytosis and exocytosis. Endocytosis : It involves intake of materials in the form of carrier vesicles formed by invagination of small regions of plasma membrane. Endocytosis is of three types : (i) phagocytosis (ii) pinocytosis and (iii) receptor-mediated endocytosis. (i) Phagocytosis : It is the process by which extracellular substances (bacteria, dead tissue, foreign particles etc.) are engulfed by the cells. The substance makes contact with the cell membrane, which then invaginates. The endocytic vesicle pinches off from the cell membrane and fuses with another intracellular vesicle e.g., lysosome, from which the ingested substance is released into ICF. (ii) Pinocytosis : Fluid materials having high molecular weight such as proteins, amino acids, fats, insulin, lipoproteins, etc., in the form of globules of fluid enter the cytoplasm by invagination of plasma membrane. Pinocytosis is initiated when the plasma membrane is stimulated by certain chemical substances. A liquid droplet at the point of contact forms infolding of cell membrane in sac like structure into which this fluid food is drawn in. Globules of fluid materials are called pinosomes which are pinched off from the plasma membrane inside the cytoplasm in the form of small pinocytic vesicles. (iii) Receptor-mediated endocytosis : The material to be transported first binds to a receptor, and then the receptor-substance complex is ingested by endocytosis. For example, transport of iron and cholesterol into the cell. Exocytosis: Substances secreted by the cell are trapped within vesicles or granules which fuse with the cell membrane and release their contents to the extracellular fluid. This leaves the contents of the vesicles or granules outside the cell. Hormones, digestive enzymes and synaptic transmitters are examples of substances transported out of the cell by this process.
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Functions of lysosomes ●● Lysosomal enzymes digest proteins into dipeptides and carbohydrates into m o n o s a c c h a r i d e s. Some disaccharides (sucrose) and polysaccharides (inulin, dextran) are not digested and remain in the lysosomes. ●● Lysosomes are involved in the renovation and turnover of cellular components by process of autophagy. ●● Lysosomes are active in the remodeling of tissues (e.g., removal of the tadpole tail, regression of Wolffian and Muller’s ducts, etc.) in development. Acrosome The acrosome of the spermatozoon, which develops form the Golgi region and covers the anterior end of the nucleus, can be considered as a special lysosome. Indeed, it contains protease and hyaluronidase (an enzyme that digests cell coats containing hyaluronic acid) and abundant acid phosphatase. During fertilization of the oocyte, hyaluronidase disperses the cells around it (cumulus oophorus) and protease digests the zona pellucida, making a channel through which the sperm nucleus penetrates. In eggs, lysosomes play a role in the digestion of the stored reserve materials. ●●
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●●
●●
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Certain diseases are caused by nondigestion of certain components due to absence of required enzymes in the lysosomes. Most of the diseases result from accumulation of glycolipids and mucopolysaccharides. A number of other diseases are linked to malfunctioning of lysosomes like arthritic joints, gout and lung fibrosis. Some 20 genetic or congenital diseases occur in human beings due to deficiency of certain lysosomal enzymes, i.e., Hunter’s syndrome, Farber’s disease etc. Accidental or pathological release of hydrolases from lysosomes causes breakage of chromosomes, their abnormal distribution during mitosis. Cancer is also caused by such a change. The glycosidation of lipids, which leads to the synthesis of gangliosides and glycosphingolipids, may be altered in cancerous cells. Digestion of extracellular material involves the release MT BIOLOGY
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of primary lysosomes by exocytosis (e.g., osteoclasts may do so by the release of lysosomal enzymes that degrade the organic matrix). In rheumatoid arthritis lysosomal enzymes erode the cartilage of joints. ●● Crinophagy is a process by which excess secretory granules are removed by lysosomes. Lysosomal enzymes of sperm acrosome ●● dissolve the egg membrane for the entry of sperm into ovum during fertilization.
gerl machinery ●● The study of cell secretion in relation to the ER and the Golgi system is justified because these organelles are directly involved in the synthesis, transport and release of macromolecules from the cell. ●● According to current concepts, primary lysosomes are thought to be secretion products of the cell which, like other secretions, are synthesized by ribosomes, enter the ER, and reach the Golgi region for final packaging. ●● Since by this mechanism a cell may produce different types of lysosomes, and many other secretion products, it is likely that there is a topological specificity in the ER-Golgi system. ●● Studies on the biosynthesis of the lysosomal enzymes cathepsin and b-glucuronidase favour the biogenesis of lysosomal enzymes on ribosomes bound to the ER. ●● Lysosomal enzymes are discharged into the ER lumen using a signal peptide mechanism similar to that of secretory proteins. ●● Lysosomal enzymes contain terminal mannose-6phosphate (man-6-P) residues that interact with man-6-P receptors in intracellular membranes. ●● After being secreted into the ER lumen the enzymes are glycosylated. Later on, the addition of the man-6-P residue is catalyzed by enzymes that are associated with the Golgi complex. ●● Newly synthesized lysosomal enzymes, bearing the man6-P recognition marker, bind to specific man-6-P receptors located in Golgi membranes and are then removed from the Golgi cisternae and delivered to the GERL region and to the lysosomes by a vesicular carrier. ●● After reaching its final destination the terminal man-6-P residue is cleaved off.
Multiple Choice Questions 1. Which of the following is a part of endomembrane system of eukaryotic cell? (a) Peroxisomes (b) Chloroplasts (c) Mitochondria (d) Golgi complex 2. Golgi complex is associated with (a) packaging and storage of material (b) formation of new cell wall (c) secretion of different substances (d) all of the above. 3. The most important function of rough endoplasmic reticulum (RER) is (a) provides surface for protein synthesis (b) nourishing the nucleus (c) secretion of materials (d) to give shape to the cell. 4. When the region of endoplasmic reticulum is studded by ribosomes on the outer surface of the cisternae, it is called (a) Sarcoplasmic reticulum (b) Smooth endoplasmic reticulum (c) Granular endoplasmic reticulum (d) None of the above. 5. Which of the following is not function of Golgi bodies? (a) Secretion (b) Formation of plasma membrane (c) Fat synthesis (d) Cell wall formation 6. Which of the following is the site of lipid synthesis? (a) Rough ER (b) Smooth ER (c) Golgi bodies (d) Ribosome 7. Secondary lysosomes are also called (a) autophagic vacuoles (b) lipofuscin granules (c) residual body (d) heterophagosomes. 8. What would happen if lysosomes get ruptured inside the cells in which they are present? (a) Cells will swell. (b) Cells will shrink. (c) Cells will die. (d) Nothing would happen. 9. Ribosomes are attached to ER through (a) riboplasm (b) rRNA (c) tRNA (d) ribophorins. 10. Golgi apparatus is absent in (a) most prokaryotic cells (b) mature RBCs of mammals (c) mature sieve tubes of plants (d) all of these.
11. Zone of exclusion is associated with (a) Golgi complex (b) endoplasmic reticulum (c) mitochondria (d) chloroplast. 12. Which of the following statements is incorrect with reference to lysosomes? (a) They are filled with acid hydrolases and other enzymes. (b) They are monomorphic and uniform in structure and function. (c) They may be autophagic vacuoles. (d) They can digest most of proteins, lipids and polysaccharides. 13. Which of the following cell organelles helps in the formation of desmotubules which extend through plasmodesmata? (a) ER (b) Plasma membrane (c) Mitochondria (d) Tonoplast 14. Ribophorins are required for (a) synthesis of ribosomes in nucleolus (b) attachment of ribosomes over RER (c) attachment of ribosomal subunits (d) attachment of ribosomes to mRNA. 15. Match Column I with Column II and select the correct answer using the codes given below. Column I Column II A. Pinocytosis 1. Ephagy B. Phagocytosis 2. Transport of cholesterol C. Exocytosis 3. Cell drinking D. Receptor mediated 4. Cell eating endocytosis (a) A-3, B-4, C-1, D-2 (b) A-2, B-1, C-3, D-4 (c) A-4, B-1, C-2, D-3 (d) A-3, B-2, C-1, D-4 16. Read the following statements regarding the structure of Golgi complex. 1. The cis face of cisternae is associated with nuclear envelope. 2. Tubules are large, independent structures arising from the centre of cisternae. 3. Vesicles are small, flat, tube like structures present at the edge of cisternae face. 4. Golgian vacuoles are large spherical vacuoles produced at maturing face. Which of these statements are correct? (a) 1 and 2 (b) 1, 2 and 3 (c) 1 and 4 (d) None of these MT BIOLOGY
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17. Besides giving out secretory vesicles, the Golgi apparatus is also concerned with formation of (a) ribosomes (b) endoplasmic reticulum (c) lysosomes (d) mitochondria.
18. Which of the following is not the function of lysosome? (a) Disappearance of tail during the metamorphosis of the frog’s tadpole. (b) Autolysis of the cellular contents. (c) Dissolution of the egg membrane during fertilization. (d) Secretion of mucilage for the lubrication of root tip.
22. Choose the incorrect statement about Golgi apparatus (GA). (a) The main function of GA is to process, package transport and release secretory proteins. (b) Zone of exclusion is filled with a number of organelles. (c) GA causes glycosidation of lipids and proteins. (d) Acrosome of sperm is synthesized by GA.
19. Match Column I with Column II and select the correct option. Column I Column II A. Camilio Golgi 1. Lysosome B. Porter and Thompson 2. Endoplasmic reticulum C. de Duve 3. Golgi apparatus (a) A-3, B-2, C-1 (b) A-1, B-2, C-3 (c) A-2, B-1, C-3 (d) A-3, B-1, C-2 20. The acidic conditions for the hydrolytic enzymes in lysosomes are maintained by (a) pumping protons into the interior of lysosomes (b) membrane destabilizers (c) presence of about 50 enzymes (d) all of the above 21. Which of the following statements regarding endoplasmic reticulum is not correct? (a) Granular ER provides surface for protein synthesis. (b) Cisternae are involved mainly in lipid and sterol synthesis.
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(c) Tubules form reticular system alongwith the cisternae and vesicles. (d) Endoplasmic reticulum provides support to the colloidal protoplasm.
23. Which face of Golgi complex give rise to the secretory vesicles? (a) Trans face (b) Cis face (c) Convex face (d) Proximal face 24. Autophagic vacuoles are formed (a) from digestive vacuoles containing only undigested material (b) by union of many primary lysosomes around old organelles (c) when phagosomes fuse with already existing primary lysosome (d) as new structures budded from Golgi apparatus. 25. Lysosome containing the food material to be digested is referred to as (a) primary lysosome (b) secondary lysosome (c) residual bodies (d) cytosome. Answer key 1. (d) 6. (b) 11. (a) 16. (c) 21. (b)
2. (d) 7. (d) 12. (b) 17. (c) 22. (b)
3. 8. 13. 18. 23.
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MT BIOLOGY
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4. 9. 14. 19. 24.
(c) (d) (b) (a) (b)
5. 10. 15. 20. 25.
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(a) (c) (a) (d) (a)
(c) (d) (a) (a) (b) nn
1. An ecosystem which can be easily damaged but can recover after some time if damaging effect stops will be having (a) low stability and high resilience (b) high stability and low resilience (c) low stability and low resilience (d) high stability and high resilience. 2. When a big fish eats a small fish which eats water fleas supported by phytoplankton, water fleas are (a) producers (b) primary consumers (c) secondary consumers (d) top consumers. 3. Correct sequence of stages of succession on a bare rock is (a) Lichens → Mosses → Grasses → Shrubs → Trees (b) Trees → Shrubs → Lichens → Mosses → Grasses (c) Mosses → Shrubs → Trees → Lichens → Grasses (d) Mosses → Lichens → Grasses → Shrubs → Trees Direction (Q. 4 and 5): Study the food web given below and answer the questions that follow.
4. Which of the following organisms in the given food web act both as a predator and a prey? (a) I, II and IV (b) II, III and V (c) II, III, V, VI and VII (d) II, III and VI
5. Which of the following organisms in the given food web act as a secondary consumer? (a) II and V (b) III and VI (c) VII only (d) IV only 6. Productivity is the rate of production of biomass
expressed in terms of (i) (kcal m–3) yr–1 (iii) (gm–1) yr–1 (a) (ii) and (iii) (c) (ii) and (iv)
(ii) (gm–2) yr–1 (iv) (kcal m–2) yr–1 (b) (iii) and (iv) (d) (i) and (iii).
7. Match Column - I with Column - II and select the correct
option from the codes given below. Column - I Column - II A. Standing state (i) Fast and maintain nutrient circulation B. Gaseous cycles (ii) Amount of nutrients present in soil at any given time C. Standing crop (iii) Slow; nutrients may get out of circulation D. Sedimentary cycles (iv) Amount of living matter present in an ecosystem (a) A - (ii), B - (i), C - (iv), D - (iii) (b) A - (iii), B - (i), C - (iv), D - (ii) (c) A - (i), B - (iii), C - (ii), D - (iv) (d) A - (ii), B - (iii), C - (iv), D - (i) 8. Given below are some of the stages of the hydrarch. A. Marsh meadow stage B. Reed swamp stage C. Submerged plant stage D. Phytoplankton stage E. Free-floating plant stage MT BIOLOGY
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Select the correct sequence of these stages. (a) D, C, E, B and A (b) C, E, A, B and D (c) B, D, C, A and E (d) D, E, C, B and A
9. Which of the following is an abiotic component of the ecosystem? (a) Bacteria (b) Plants (c) Humus (d) Both (a) and (c) 10. Which of the following representations shows the pyramid of numbers in a forest ecosystem? (a)
(c)
(b)
(d) None of these
11. Percentage of photosynthetically active radiation (PAR) that is captured by plants in synthesis of organic matter is (a) 50 - 70% (b) 30 - 40% (c) 80 -100% (d) 2 - 10%. 12. Among the following, where do you think the process
of decomposition would be the fastest? (a) Tropical rain forest (b) Antarctic region (c) Dry arid region (d) Alpine region 13. The process of mineralisation by micro-organisms helps
in the release of (a) inorganic nutrients from detritus and formation of humus (b) both organic and inorganic nutrients from detritus (c) organic nutrients from humus (d) inorganic nutrients from humus. 14. Read the given statements and select the correct
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option. Statement 1 : Ecological pyramids are not the perfect representation of an ecosystem. Statement 2 : Saprophytes are not given any place in ecological pyramids. (a) Both statements 1 and 2 are correct and statement 2 is the correct explanation of statement 1. (b) Both statements 1 and 2 are correct but statement 2 is not the correct explanation of statement 1. (c) Statement 1 is correct and statement 2 is incorrect. (d) Both statements 1 and 2 are incorrect. MT BIOLOGY
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15. Read the given statements and select the correct
option. Statement 1 : Dry weight is more accurate than fresh weight for calculation of biomass. Statement 2 : Dry weight do not give weightage to water or moisture, amount of which might vary at different trophic levels or environment. (a) Both statements 1 and 2 are correct and statement 2 is the correct explanation of statement 1. (b) Both statements 1 and 2 are correct but statement 2 is not the correct explanation of statement 1. (c) Statement 1 is correct and statement 2 is incorrect. (d) Both statements 1 and 2 are incorrect. 16. The available biomass for consumption to heterotrophs is (a) net primary productivity (b) gross primary productivity (c) secondary productivity (d) standing state. 17. During the process of ecological succession the changes that take place in communities are (a) orderly and sequential (b) random (c) very quick (d) not influenced by the physical environment. 18. Which of the following is incorrect regarding phosphorus cycle? (a) Adding NPK fertilizers to soil will interfere with phosphorus cycle. (b) Soils and rocks are major reservoir of phosphorus. (c) Atmospheric input of phosphorus through rainfall is equivalent to that of carbon. (d) There is no respiratory release of phosphorus into atmosphere. 19. Which of the following explains the concept of food web most appropriately? (a) Various interlinked food chains in a community. (b) Relationship between animals and plants. (c) Relationship between organisms and their environment. (d) Relationship between animals, plants and microbes. 20. Given figure represents a pyramid of biomass in an aquatic ecosystem.
Identify A and B and select the correct answer. (i) A is the species which supports and B is the species which is supported. (ii) A is the species which is supported and B is the species which supports. (iii) A is phytoplanktons and B is zooplanktons. (iv) A is zooplanktons and B is phytoplanktons. (a) (i) and (iv) (b) (ii) and (iii) (c) (i) and (iii) (d) (ii) and (iv)
21. Select the option that correctly identifies A, B and C in the given table. Organism Eagle Earthworm Frog
A (a) Top carnivore (b) Top carnivore (c) Secondary consumer (d) Scavenger
Trophic level A Primary consumer C
(b) (i), (ii) and (iii) (d) (i), (ii) and (iv)
26. Arrange the following ecosystems in increasing order
of their mean net primary productivity (tonnes / ha / year). A. Tropical deciduous forest B. Temperate coniferous forest C. Tropical rain forest D. Temperate deciduous forest (a) B < A < D < C (b) D < B < A < C (c) A < C < D < B (d) B < D < A < C
Food chain Grazing B Grazing
27. Which of the following will be present at the beginning
B C Detritus Secondary consumer Detritus Primary consumer Grazing Secondary consumer
28. Which of the following is correct regarding hydrosere?
Grazing Producer
22. In a particular food chain, energy at producer level is
33 kJ. What will be the amount of energy present at the level of tertiary consumer? (a) 33 kJ (b) 330 J (c) 33 J (d) 3.3 J 23. Xerach succession will ultimately lead to _____
condition. (a) hydric (c) xeric
(a) (i) and (ii) (c) (iii) and (iv)
(b) mesic (d) none of the above
24. Which one of the following should not be used for construction of ecological pyramids? (a) Fresh weight (b) Dry weight (c) Number of individuals (d) Rate of energy flow 25. Read the following statements and select the correct
ones. (i) Secondary succession is faster than primary succession. (ii) Lichens are usually pioneer species on bare rocks. (iii) Pyramid of energy can be inverted if you take sunlight into consideration (iv) Number of trophic levels in grazing food chain are restricted by the transfer of energy.
of a detritus food chain? (a) Grasses (b) Bacteria (c) Zooplankton (d) None of these (a) Hydrilla and Potamogeton occur in submerged stage. (b) Phragmites and Typha occur in reed swamp stage. (c) Alnus and Populus occur in woodland stage. (d) All of these. 29. Ecologists generally separate organisms in an
ecosystem into three categories (producer, consumer and decomposer) based on (a) how they obtain their energy (b) how rapid their metabolism is (c) the rate of succession in the ecosystem (d) the size and complexity of the ecosystem. 30. Primary productivity is
(a) equal to the standing crop of an ecosystem (b) the greatest in freshwater ecosystems (c) the rate of conversion of light to chemical energy in an ecosystem (d) inverted in some aquatic ecosystems.
ANSWERS
WHO AM I ...
1. Skeletal muscle fibre
Pg. 27
2. Schwann cell
Pg. 37
3. Secondary medullary rays
Pg. 50
4. Wound cambium
Pg. 51
5. Zone of exclusion
Pg. 64 MT BIOLOGY
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31. The diagram shows a pyramid of numbers in an
ecosystem on land. Which organisms are the smallest in size? (a) P (b) Q (c) R (d) S 32. What amount of energy will be available to decomposers?
Direction (Q. 35 and 36): Refer to the food webs given below with arrows indicating flow of energy.
35. Which of the following would probably have the
greatest total biomass? (a) F
(a) 100 J (b) 67 J (c) 6 J (d) 33 J 33. Study the given diagram with arrows representing direction of movement of carbon compounds in animals, plants, atmosphere and decomposers. Identify 1, 2, 3 and 4.
(a) (b) (c) (d)
1
2
3
4
Atmosphere Animals Decomposers Plants Plants Atmosphere Animals Decomposers Animals Decomposers Plants Atmosphere Atmosphere Decomposers Plants Animals
34. In the given food web, an increase in the population of hawks will not result in
(a) (b) (c) (d) 70
decrease in the population of rabbits and snakes increase in the population of producers increase in the population of lizards increase in the population of grasshoppers.
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(b) J + G
(c) K
(d) K + M
36. Which species is considered decomposer? (a) F (b) G (c) H (d) K 37. In an open ocean, the biomass of primary producers
(microscopic algae) is often lower than the biomass of higher trophic levels (zooplanktons and fish). How can there be enough food in an open ocean to support the higher trophic levels? (a) The microscopic primary producers are a source of food of high quality. (b) The microscopic primary producers have high rates of growth and reproduction. (c) The higher trophic levels are occupied by coldblooded animals which do not require much food. (d) The animals at higher trophic levels are efficient predators. 38. Given below is a table of factors affecting microbial decomposition. (‘+’ means ‘favouring’ and ‘–’ means inhibiting or lowering). Select the correct option. High temperature
Lack of Moist oxygen environment
Lignin and chitin in detritus (a) + + + – (b) + – + – (c) – – + – (d) – + + – 39. Which of the followings ways are the most direct for release of carbon as CO2 in atmosphere? I. Combustion of fossil fuels II. Starch grains eaten by birds
(a) Pyramid ‘a’ reflects energy losses due to respiration within trophic levels and energy losses during energy transfer between trophic levels. (b) Pyramid ‘b’ represents an ecosystem with slow turnover in the primary consumer level. (c) For each ecosystem, its energy pyramid is opposite to its biomass pyramid. (d) For both ecosystems, production efficiency becomes higher as the trophic level increases.
III. Bread eaten by humans IV. Burning of starch grains V. Formation of calcareous sediments in water (a) II, III and V (b) I, III and V (c) I, IV and V (d) I and IV 40. Pyramid shown below is a typical number pyramid in which producers have been omitted.
43. The diagram below represents the relationships between
organisms in a remote pond ecosystem. From this information, which of the following is the most likely to be correct?
If the above pyramid is converted into a biomass pyramid, it will take the shape of (a)
(b)
(c)
(d)
41. Succession in a forest ecosystem is characterized by
changes in species diversity, biomass and net primary productivity as shown in the graph below. Identify curves A, B and C.
a. A: biomass B: net primary productivity C: species diversity b. A: species diversity B: net primary productivity C: biomass c. A: net primary productivity B: biomass C: species diversity d. A: net primary productivity B: species diversity C: biomass 42. The figure below shows standing biomass pyramids of two ecosystems, each with four trophic levels.
44. The graphs below show the variations in the populations of producers, primary consumers and secondary consumers as well as the amount of dissolved mineral salts in a pond.
Which of the following is correct regarding them?
From this information, which of the following is the most likely to be correct? (a) DDT present in the ecosystem would accumulate to the highest concentrations in the tissues of Detritivore 1. (b) The introduction of Consumer 4 individuals from an external population would lead to a temporary increase in numbers of Producer 2. (c) Disease in the Producer 1 population would lead to an increase in the Producer 3 population. (d) Extermination of Consumer 3 would cause a sustained increase in the population of Consumer 2.
Which one of the following correctly matches each graph? MT BIOLOGY
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Producer Population
Primary Secondary Amount of consumer consumer dissolved population population mineral salts
(a)
Z
Y
X
W
(b)
W
X
Y
Z
(c)
W
Y
X
Z
(d)
X
Z
Y
W
45. The organic matter (humus and dead plant tissues) in the soils of the boreal forest biome forms one of the largest pools of C in the biosphere. On average, boreal forest soils contain 15,000 g Cm–2, a higher value than in other types of forest. However, the primary production of the boreal forest is only 350 g Cm–2Yr–1 on average, a low value compared to other types of forests. This pattern occurs primarily because (a) high rates of herbivory in the boreal forest lead to low levels of forest productivity. (b) the slow weathering of bedrock under boreal forest soils releases large quantities of C into the soil. This C would be lost in hotter climates. (c) low rates of herbivory in the boreal forest mean that most leaves, branches, and roots are added to the soil when they die. Temperate and tropical forests, in contrast, have high rates of herbivory. (d) the cold, wet soils of the boreal forest restrict decomposition more than they restrict the photosynthesis of plants. 46. Given below is a diagram of food web of a terrestrial ecosystem. The arrows represent energy flow and the letters represent different species. In which species would a toxic pollutant that accumulates in animals probably reach the highest concentration?
48. The graph shows the productivity of an aquatic ecosystem
measured in terms of dissolved oxygen produced and consumed by green plants and photosynthetic algae where PS = photosynthesis and R = respiration.
What will happen during the algal bloom? (a) PS will be increased, R will be decreased (b) PS will be decreased, R will be increased (c) PS and R will not change (d) PS + R will increase 49. In an ecosystem, (a) energy is recycled through the trophic structure (b) energy is usually captured from sunlight by primary producers, passed to secondary producers in the form of organic compounds, and lost to decomposers in the form of heat. (c) chemicals are recycled between the biotic and abiotic sectors, whereas energy makes a one-way trip through the food web. (d) there is a continuous process by which energy is lost as heat, and chemical elements leave the ecosystem through runoff. 50. Given figure shows energy flow along a food chain.
How much energy in kJ is lost in waste products from herbivores?
(a) 2700
(c) 1200
(d) 1440
Answer key
(a) Species D (b) Species B (c) Species C (d) Species E 47. In ecological pyramids, normally each higher trophic level is smaller. Possible exceptions leading to inverted pyramids are I. A pyramid of numbers with one big producer. II. A pyramid of mass when producers have a very short life cycle. III. A pyramid of energy in extremely hot ecosystems. Which combination is correct? (a) I and II (b) II and III (c) I and III (d) I, II and III 72
(b) 1350
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1. 6. 11. 16. 21. 26.
(a) (c) (d) (a) (a) (d)
2. 7. 12. 17. 22. 27.
(b) (a) (a) (a) (c) (b)
3. 8. 13. 18. 23. 28.
(a) (a) (d) (c) (b) (d)
4. 9. 14. 19. 24. 29.
(c) (c) (a) (a) (a) (a)
5. 10. 15. 20. 25. 30.
(b) (b) (a) (c) (d) (c)
Higher Order Thinking Skills Questions (HOTS) 31. (a) 32. (b) 33. (b) 34. (c) 35. 36. (d) 37. (b) 38. (b) 39. (d) 40. 41. (d) 42. (a) 43. (b) 44. (c) 45. 46. (d) 47. (a) 48. (d) 49. (c) 50.
(a) (a) (d) (c) nn
nitrogen fixing cyanobacteria Anabaena, thus aiding in nitrogen fixation. Hence, some rice fields are regularly provided with Azolla.
1. Differentiate between BOD and COD. Ans. Biological Oxygen Demand (BOD) refers to the amount of dissolved oxygen (DO) needed by bacteria for decomposing the organic wastes present in water. It indicates the quality of waste water. Chemical Oxygen Demand (COD) is the amount of oxygen required to oxidize all the reducing substances present in water. It includes BOD, reduced chemicals produced during putrefaction and other oxygen demanding chemicals. 2. What is photochemical smog? Where was it first observed? Ans. Photochemical smog is grey or yellowish brown, opaque smog formed at high temperature over cities and towns due to still air, emission of nitrogen oxides and volatile hydrocarbons from automobile exhausts and solar energy. It contains secondary pollutants. It was first reported over Los Angeles in 1940s. 3. How did Weismann disprove Lamarck’s theory of acquired characters? Ans. August Weismann, in 1892, performed the decaudalisation experiments on mice and disproved Lamarckism and pangenesis theory of Darwin. He cut the tail of white mice for more than 20 generations and observed the effect on the length of tail in coming generations. In all generations, the length of the tail was found to be normal. Hence, he believed that the acquired characters were not inherited. 4. Describe the principle of immunisation or vaccination. Ans. The principle of immunisation or vaccination is based on the property of ‘memory’ of immune system. In vaccination, a preparation of antigenic proteins of pathogen or inactivated/weakened pathogens (vaccine) are introduced into the body. The antibodies thus produced in the body against these antigens would neutralise the pathogenic agents during actual infection. 5. In some South-Asian countries, rice fields are regularly provided with Azolla. Why? Ans. Azolla pinnata is a free-floating freshwater fern which multiplies rapidly, doubling every 5-7 days. The fern can coexist with rice plants as it does not interfere with their growth. Azolla forms symbiotic association with
6. A group of bacteria was found in hot sulphur spring where the temperature was high and pH was low. How do they exist in such hostile environment? Ans. Thermoacidophiles, a type of archaebacteria, are capable of withstanding extremely low pH and high temperature due to the presence of branched chain lipids in the cell membrane and resistant enzymes which can operate under acidic conditions. 7. How do protistans reproduce under favourable and unfavourable conditions? Ans. Under favourable conditions protistans reproduce generally by asexual methods like binary or multiple fission and during unfavourable conditions, they reproduce by budding, encystment, sporulation, etc. 8. You wish to clone a DNA fragment of size 1.5 Mb. Which vector would you use? Describe it. Ans. Yeast Artificial Chromosome or YAC vectors are used to clone DNA fragments of more than 1 Mb (10 6 bp) in size. These vectors contain telomeric sequence, centromere and autonomously replicating sequence from yeast chromosomes. It also contain recognition sites for restriction enzymes and genes which act as selectable markers in yeast. They have been used extensively in mapping large genomes e.g., human genome project. 9. Why male Anopheles mosquitoes do not serve as a vector for malarial parasite? Ans. The male Anopheles mosquito feeds only on nectar and do not bite humans, hence it does not serve as a vector for malarial parasite. The female Anopheles mosquito feeds on blood and serves as vector (carrier) of malarial parasite. 10. Two closely related plants were crossed to develop a pure line. However, after a few generations a decline in vigour and yield was observed. What can be the cause of such observations? Ans. The mating of individuals closely related by ancestry is called inbreeding. It produces some ill effects such as loss of vigour and declined yield because of a phenomenon called inbreeding depression. This occurs due to increase in homozygosity in recessive alleles.
and the winner is ............. Seema Das, Bhubaneswar MT BIOLOGY
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Useful for National and All State Level PMTs 1. A specimen or other element selected to serve as nomenclatural type as long as all of the material on which the description of the new species was based is missing is called (a) syntype (b) neotype (c) isotype (d) lectotype 2. Consider the following statements and select the incorrect ones. I. All prokaryotic organisms were grouped together under kingdom Monera. II. The unicellular eukaryotic organisms were placed in kingdom Protista. III. Chlorella and Chalamydomonas, both have cell walls. IV. Paramecium and Amoeba lack cell walls. V. Kingdom-Protista has brought together Chlamydomonas and Chlorella with Paramecium and Amoeba. (a) I, II, and III (b) I and III (c) III, IV and V (d) None of these 3. Which of the following bacteria play a main role in recycling the nutrients like nitrogen, phosphorus, iron and sulphur? (a) Chemoheterotrophic bacteria (b) Chemolithoautotrophic bacteria (c) Parasitic bacteria (d) Saprophytic bacteria 4. Red tides develop in coastal water is mainly due to the presence of (a) dinoflagellates (b) euglenoid forms (c) diatoms and desmids (d) slime moulds. 5. Male and female gametophytes are independent and free-living in (a) mustard (b) castor (c) Pinus (d) Sphagnum. 6. Oogamous means (a) fusion between female and male gametes, both of similar size. 74
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(b) fusion between one large female gamete and a smaller non-motile male gamete. (c) fusion between one large female gamete and a smaller motile male gamete. (d) fusion between one smaller female gamete and a large motile male gamete. 7. A plant growing wild in one country was brought to another with the same latitude and at the same height from sea level. However, the plant did not multiply. The possible causative factor for this is (a) temperature difference (b) difference in the length of the day (c) absence of a specific vector (d) humidity difference. 8. Match column - I with column - II and select the correct option from the codes given below. Column - I Column - II A. Phycomycetes (i) Alternaria and Trichoderma B. Ascomycetes (ii) Agaricus and Ustilago C. Basidiomycetes (iii) Aspergillus, Claviceps and Neurospora D. Deuteromycetes (iv) Mucor, Rhizopus and Albugo (a) A - (i), B - (iv), C - (iii), D - (ii) (b) A - (ii), B - (i), C - (iv), D - (iii) (c) A - (iv), B - (iii), C - (ii), D - (i) (d) A - (iii), B - (ii), C - (i), D - (iv) 9. In gymnosperms, the pollen chamber represents (a) a cell in the pollen grain in which the sperms are formed. (b) a cup-shaped cavity in the ovule in which pollen grains are stored after pollination. (c) an opening in the megagametophyte through which the pollen tube approaches the egg. (d) the microsporangium in which pollen grains develop.
10. Select the option which correctly matches the phylum with its general features. (a) Annelida – Exhibit bilateral true symmetry, metamerism and true coelom (b) Echinodermata – Exhibit tissue level organisation and radial symmetry (c) Arthropoda – Exhibit incomplete digestive system and segmentation (d) None of these 11. Which of the following is incorrect for animals belonging to same class as Trygon? (a) Presence of placoid scales. (b) Absence of air bladder. (c) Presence of cartilaginous endoskeleton. (d) Notochord persistent only at larval stage, after that it disappears. 12. Biomagnification of DDT in an aquatic food chain starting from water having a concentration of 0.003 ppm may go, in fish eating birds, upto (a) 2 ppm (b) 25 ppm (c) 50 ppm (d) 100 ppm. 13. Match column - I with column - II and select the correct option from the codes given below. Column - I Column - II A. Apple (i) Persistant bracts B. Coconut (ii) Fleshy thalamus C. Jackfruit (iii) Pulpy endocarp D. Guava (iv) Stony endocarp E. Pineapple (v) Fleshy perianth (a) A - (ii), B - (iii), C - (iv), D - (v), E - (i) (b) A - (v), B - (iii), C - (i), D - (iv), E - (ii) (c) A - (ii), B - (iii), C - (i), D - (v), E - (iv) (d) A - (ii), B - (iv), C - (v), D - (iii), E - (i) 14. In plants X and Y, a slender lateral branch arises from the base of the main axis and after growing aerially for sometimes, arch downwards to touch the ground. X and Y are (a) Mint and Jasmine (b) Pistia and Eichhornia (c) Strawberry and Rose (d) Bougainvillea and Ruscus. 15. Collenchymatous cells have thickened corners due to the deposition of (a) cellulose (b) hemicellulose (c) pectin (d) all of these. 16. Which of the following forms interfascicular cambium? (a) Medullary rays to xylem cambium. (b) Medullary rays to intrafascicular cambium. (c) Medullary rays to lateral fascicular cambium. (d) Endodermis to intrafascicular cambium. 17. Read the given statements and select the correct option.
Statement 1 : In Golgi complex, the cisternae have cis face and trans face. Statement 2 : The cis face and trans face of Golgi complex are called maturing face and forming face respectively. (a) Both statements 1 and 2 are correct and statement 2 is the correct explanation of statement 1. (b) Both statements 1 and 2 are correct but statement 2 is not the correct explanation of statement 1 (c) Statement 1 is correct and statement 2 is incorrect. (d) Both statements 1 and 2 are incorrect. 18. Allosteric modulation inhibits the action of enzymes by (a) competitive inhibition (b) increasing substrate concentrations (c) by reacting with products of reaction (d) changing enzyme concentrations. 19. Z is a phase of equational cell division, in which the chromatin condenses into discrete chromosomes. During this phase, nuclear envelope breaks down and spindles forms at opposite ends of the cell. Identify this phase. (a) Interphase (b) Anaphase (c) Telophase (d) Prophase 20. During synthesis phase of cell cycle (a) the number of chromosome doubles (b) the number of chromosome doubles only in case of diploid cell (c) the number of chromosome doubles only in the case of haploid cell (d) there is no change in chromosome number. 21. Which of following is necessary in the process of facilitated diffusion? (a) Concentration gradient (b) Carrier protein (c) Hydrophilic moeity (d) All of these 22. Which of the following occurs during manganese toxicity in plants? (a) Reduction in uptake of iron and magnesium. (b) Appearance of brown spots surrounded by chlorotic veins. 2+ (c) Inhibition of Ca ions translocation in the shoot apex. (d) All of these. 23. In photosynthetic plants, Light Harvesting Complex (LHC) consists of (a) one molecule of chlorophyll-a (b) very few molecules of chlorophyll-a (c) hundreds of pigment molecules bound to proteins (d) chlorophyll-a, chlorophyll-c, proteins and DNA. MT BIOLOGY
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24. Example of oxidative decarboxylation is pyruvate (a) oxidised to carbon dioxide (b) subsidised to oxygen (c) oxidised to oxygen (d) subsidised to carbon dioxide. 25. Plant growth regulators (PGRs) or plant hormones are generally (a) produced from many parts of plant (b) produced from shoot apices and stem apices (c) produce single effect (d) basic in nature. 26. Refer to the figure showing gastric glands and select the correct statement for A – D. (a) A is present throughout the epithelium and secretes mucus. (b) B secretes hydrochloric acid and castle intrinstic factor. (c) C secretes gastric digestive enzymes. (d) D produces serotonin and histamine. 27. Select the correct option for P, Q and R that completes the given data regarding partial pressure of O2 and CO2. Partial pressure of gases (mmHg)
De oxygenated blood
Oxygenated blood
Tissues
O2 CO2
40 P
Q 40
40 R
Choose the correct option for A, B and C to complete the given data. (a) P-40, Q-95, R-40 (b) P-45, Q-95, R-45 (c) P-35, Q-95, R-45 (d) P-35, Q-95, R-95 28. Atrio-ventricular valves, bicuspid and tricuspid, opens when (a) blood from the pulmonary artery and vena cava flows into the left and right ventricles, respectively (b) blood from the pulmonary vein and aorta flows into the right and left ventricles, respectively (c) blood from the pulmonary vein and aorta flows into the right and left atrium, respectively (d) oxygen from the pulmonary vein and aorta flows into the left and right atrium, respectively. 76
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29. The pacemaker of heart is called so because (a) it can change the contractile activity generated by AV node (b) it delays the transmission of impulse between the atria and ventricles (c) it gets stimulated when it receives neural signals (d) it initiates and maintains the rhythmic contractile activity of heart. 30. Renin - Angiotensin - Aldosterone System is (a) triggered when juxta-glomerular cells of JGA releases renin in response to various stimuli (b) responsible for regulation of kidney function (c) a powerful mechanism responsible for regulation of functioning of heart (d) both (a) and (b). 31. The part of the brain which is associated with strong emotions is (a) limbic system (b) medulla (c) cerebellum (d) cerebral cortex. 32. Malleus, incus and stapes (a) equalise the pressure on either sides of the ear drum (b) collect the vibrations in air which produce the sound (c) increase the efficiency of transmission of sound waves to the inner ear (d) all of these. 33. The new potential developed on postsynaptic membrane (a) is always inhibitory (b) is always excitatory (c) may be excitatory or inhibitory (d) is neither excitatory nor inhibitory. 34. Which of the following statements are correct? I. Calcitonin regulates the metabolism of calcium. II. Oxytocin stimulates contraction of uterine muscles. III. Grave's disease is caused by thyroid gland. IV. Vasopressin stimulates reabsorption of water in renal tubules. V. Adrenaline and noradrenaline are the emergency hormones. (a) III, IV and V (b) I, II and V (c) II, III and IV (d) I, II, III, IV and V 35. How do steroid hormones work? (a) They enter into target cells and binds with specific receptor and activate specific genes to form protein. (b) They bind to cell membrane. (c) They catalyse formation of AMP. (d) None of these.
36. Which of the following options correctly mentions level of hormones during menstrual cycle? 13-14 Days FSH
LH
st
rd
21 to 23 Day
Progesterone
FSH
LH
Progesterone
(a) High High
Low
Low
Low
High
(b) High High
High
Low
Low
Low
(c)
Low
Low
Low
High
High
High
(d) Low
Low
High
High
Low
Low
37. Head region of the sperm contains (a) nucleus and acrosome (b) middle piece and neck region (c) nucleus and tail (d) middle piece and nucleus. 38. Why are polar bodies formed during oogenesis? (a) They serve both as a dumping ground for extra sets of chromosomes and ensure that the ovum will have most of the cytoplasm. (b) They rid the body of defective sets of chromosomes, leaving the 'good' set within the ovum. (c) They are merely the by-product of meiosis and serve no function. (d) They prevent the development of most sets of multiple birth. 39. Read the given statements and select the correct option. Statement 1 : MTP is considered relatively safe during the first trimester of pregnancy. Statement 2 : Foetus becomes intimately associated with the maternal tissues after the first trimester. (a) Both statements 1 and 2 are correct and statement 2 is the correct explanation of statement 1. (b) Both statements 1 and 2 are correct but statement 2 is not the correct explanation of statement 1. (c) Statement 1 is correct and statement 2 is incorrect. (d) Both statements 1 and 2 are incorrect. 40. The strength of the linkage between two genes is (a) directly proportional to the distance between them (b) inversely proportional to the distance between them (c) dependent on the size of chromosomes (d) changed after crossing over. 41. With respect to the polarity of coding strand, the promoter site and the terminator site for transcription are located at (a) 3′ (downstream) end and 5′ (upstream) end, respectively of the transcription unit
(b) 5′ (upstream) end and 3′ (downstream) end, respectively of the transcription unit (c) the 5′ (upstream) end (d) the 3′ (downstream) end. 42. Which of the following is true regarding the phenomenon of genetic drift? (i) Random change in gene allele frequency (ii) Occurs by chance (iii) It is directional (iv) Causes elimination of certain alleles (v) Causes fixation of alleles (a) (i), (ii) and (iii) (b) (iii), (iv) and (v) (c) (i), (iii) and (v) (d) (i), (ii), (iv) and (v) 43. A scientist found that a particular gene was mutated but the polypeptide coded by this gene had not changed. The mutation probably involved which of the following? (a) Deletion of one nucleotide (b) Addition of a nucleotide (c) Substitution of a nucleotide (d) Addition of three nucleotides which form a codon. 44. The class of drugs known for their effects on cardiovascular system of the body is (a) amphetamines (b) barbiturates (c) cannabinoids (d) opioids. 45. When breeding is between unrelated animals, including individuals of the same breed but having no common ancestors for 4-6 generations, it is called (a) out-crossing (b) inbreeding (c) cross-breeding (d) interspecific hybridisation. 46. Select the false statement. (a) Hybrid maize, jowar, and bajra have been successfully developed in India. (b) Saccharum barberi was originally grown in north India, but had poor sugar content and yield. (c) Agriculture accounts for approximately 33% of India's GDP and employs nearly 62% of the population. (d) None of the above 47. Biogas is pathogen free because (a) anaerobic digestion removes pathogens like bacteria (b) it is toxic to pathogens (c) during decomposition, it produces antibiotics (d) cattle dung is pathogen free. 48. Statins used as blood cholesterol lowering agents are extracted from (a) algae (b) yeast (c) virus (d) bacteria. MT BIOLOGY
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49. Identify A, B, C and D in the given diagram of E. coli cloning vector pBR322 and select the correct statement.
(a) The recognition sequence of A is 5′ GAATTC 3′ and 3′ CTTAAG 5′ (b) B acts as a selectable marker. (c) C is extracted from Bacillus amyloliquefaciens. (d) D marks the start of the replication. 50. In the construction of a recombinant DNA molecule, DNA ligase helps in (a) formation of phosphodiester bond between two DNA fragments (b) formation of phosphodiester bonds between complementary sticky ends of DNA fragments (c) ligation of all purine and pyrimidine bases (d) none of these. 51. Why Bt toxin is not toxic to human beings? (a) The toxin recognises only insect specific targets (b) Bt toxin activation requires temperature above the human body temperature (c) Bt toxin formation from pro Bt toxin which requires pH lower than one present in human stomach (d) Conversion of pro Bt toxin takes place only in highly alkaline condition 52. An example of gene therapy is (a) production of injectable hepatitis-A vaccine (b) introduction of the genes for adenosine deaminase in a person suffering from SCID (c) production of test-tube babies by artificial insemination (d) all of these. 53. Partial regulators (a) can regulate body temperature to larger extent of environmental condition (b) can regulate body temperature to limited extent of environmental condition (c) can fully regulate their internal environment (d) none of these. 54. Age structure of a population influences population growth because 78
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(a) different age groups have different reproductive capabilities (b) different age groups have same reproductive capabilities (c) more young individuals indicate decreasing population (d) all of these. 55. Genetic diversity is the measure of (a) variety in the number and richness of the species of a region (b) variety of different life forms in ecosystem (c) variety of the genetic information contained in the organisms (d) none of these. 56. Which of the following is a secondary air pollutant? (a) Hydrocarbons (b) Smog (c) Particulate matter (d) Automobile exhausts 57. Which of the following strategy is not a correct approach to reduce global warming? (a) Reducing the greenhouse gas emission by limiting the use of fossil fuels. (b) Increase the vegetation cover, particularly the forest for photosynthetic utilisation of CO2. (c) Minimising the use of nitrogen fertilizers in agriculture for reducing NO2 emission. (d) Increasing the use of air conditioners, refrigeration units and production of plastic. 58. Which of the following statements is incorrect about cell structure? (a) Plant cells have cell walls, whereas animal cells do not. (b) Ribosomes are the main sites of energy production for the cell. (c) Lysosomes function in the digestion of cellular waste products. (d) Many cellular organelles are interrelated through an endomembrane system. 59. If a human red blood cell was placed in distilled water then it would (a) shrivel (b) plasmolyse (c) dehydrate (d) not be affected. 60. The two fundamental processes that govern the dynamics of an ecosystem are (a) solar radiation and the carbon cycle (b) photosynthesis and respiration (c) the carbon cycle and photosynthesis (d) energy flow and nutrient cycling. 61. A host plant produces a toxin that is lethal to aphids feeding on its leaves. Over time, some of the aphids become immune to the toxin. In response, the host
plant begins to produce a different toxin that is lethal to aphids. This is an example of (a) commensalism (b) predation (c) mutualism (d) coevolution. 62. Which of the following statements about meiosis is correct? (a) Only somatic cells undergo meiosis. (b) Meiosis restores the original diploid condition of a population. (c) Meiosis typically results in genetic variation among the gametes produced. (d) The products of meiosis are always four cells identical to the parent cell. 63. Parents : Brown mice × White mice with with short tails long tails F1 generation : All offspring brown with long tails F2 generation : 292 mice brown with long tails 97 mice brown with short tails 103 mice white with long tails 36 mice white with short tails The results of the above cross indicate that among the original parents (a) one was homozygous dominant for coat colour and length, whereas the other was homozygous recessive for both traits (b) one was homozygous dominant for coat colour and homozygous recessive for tail length, whereas the other was homozygous recessive for coat colour and homozygous dominant for tail length (c) one was homozygous dominant for both traits, whereas the other was heterozygous for both traits (d) one was homozygous recessive for both traits, whereas the other was heterozygous for both traits. 64. The human skin contains all of the following receptors except (a) pain receptors (b) pressure receptors (c) thermoreceptors (d) chemoreceptors. 65. The process by which species from different evolutionary lineages come to resemble each other as a result of living in very similar environment is known as (a) adaptive radiation (b) convergent evolution (c) allopatric speciation (d) punctuated equilibrium. 66. If a population exceeds the carrying capacity of the ecosystem, the most likely outcome would be (a) an increase in resources to meet its needs (b) extinction of the species (c) an eventual decline in population size (d) a steady increase in population size.
67. Which of the following procedures would not be likely to lead the production of recombinant DNA? (a) Projectile bombardment of cells with DNA coated particles from a gene gun. (b) Transformation of bacterial cells with naked DNA from human cells. (c) Transformation of bacteria using phage particles (bacterial viruses). (d) The removal of a single somatic cell from a carrot and regenerating an entire plant from the cell through tissue culture. 68. Which of the following statements does not contribute to the evidence in support of evolution? (a) Species thought to be related through evolution from a common ancestor show many anatomical similarities. (b) The stages of embryological development in animals are quite similar among highly diverse types of organisms. (c) Similarities in chromosome structure, DNA sequence, and amino acid sequence suggest relationships among organisms descending through evolution from a common ancestor. (d) The observation that the most well adapted individuals do not always produce the most fit offspring. 69. Which of the following statements is not a useful feature of restriction fragment length polymorphism? (a) They can be used to detect single gene mutations in human DNA. (b) They can be used prenatally to analyse foetal cells for genetic disorders. (c) They can be used to amplify large quantities of a single gene through use of the polymerase chain reaction. (d) They can be used to detect variation in DNA sequences among individuals. 70. In which of the following groups would you place a plant which produces spores and embryos but lacks seeds and vascular tissue? (a) Fungi (b) Bryophytes (c) Pteridophytes (d) Gymnosperms. 71. The amount of nitrogen and phosphorous cycling through an ecosystem is greatly affected by local environmental conditions, such as heavy rainfall or the removal of large numbers of plants. The amount of carbon in an ecosystem is seldom significantly affected by such factors because (a) plants make their own carbon compounds through photosynthesis (b) plants absorb large amounts of carbon from the soil MT BIOLOGY
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(c) bacteria in the soil absorb large amounts of carbon (d) the primary source of carbon is the atmosphere, whereas much nitrogen and phosphorous come from the soil. 72. Most recessive sex-linked traits, such as colourblindness, show up more frequently in males than females because (a) males have no corresponding allele on their X chromosome to mask the allele carried on their Y chromosome (b) males have no corresponding allele on their Y chromosome to mask the allele carried on their X chromosome (c) females always carry at least one dominant allele for sex-linked traits because they have two X chromosomes. (d) females compensate by 'turning off' the recessive allele through dosage compensation. 73. The water runoff from an area under study showed a very high concentration of nitrate ions. This is an indication of (a) very heavy rainfall (b) drought (c) total cut down of trees (d) excessive growth of trees. 74. In the sigmoid growth curve given below, the alphabets indicate the sequence of events. Choose the correct option where the alphabet specifies the event.
(a) A = phase of slow growth B = phase of exponential growth C = phase of diminishing growth D = stationary phase (b) A = phase of rapid growth B = phase of diminishing growth C = stationary phase D = phase of slow growth (c) A = diminishing growth B = exponential growth C = slow growth D = stationary growth (d) A = stationary phase B = phase of slow growth C = phase of rapid growth D = phase of diminishing growth 80
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75. The secondary structure of proteins whose conformation may be an alpha helix is due to (a) the hydrogen bonds between a carboxyl group of one amino acid and the NH group of another amino acid (b) the hydrogen bonds between variable groups (c) the interactions between hydrophobic and hydrophilic variable groups (d) the interactions between the positively and negatively charged variable groups. 76. Monocotyledons and dicotyledons are the two subdivisions of flowering plants. Monocotyledons are distinguished from dicotyledons because monocots possess (a) floral structures in multiples of fours and fives (b) long taproots and parallel venation in their leaves (c) netted leaf venation and floral structures in multiples of three. (d) parallel leaf venation and fibrous roots. 77. Which of the following statements is true concerning plants that utilize C4 photosynthesis? (a) They only open their stomate at night. (b) They use bundle sheath cells to separate the Calvin cycle from the atmosphere. (c) They use rubisco (ribulose bisphosphate carboxylase oxygenase) to capture carbon dioxide from the atmosphere. (d) They use lenticels exclusively for gaseous exchange in order to conserve water. 78. Which of the following statements about antibodies is false? (a) Antibodies are produced by different combinations of soluble proteins in the blood called complement. (b) When antibodies bind to a bacterial cell, it may keep that cell from adhering to host cells. (c) By binding to antigens, antibodies mark those antigens for destruction by macrophages. (d) None of these. 79. During muscle contraction (a) calcium ions combine with troponin to cause a conformational change in tropomyosin (b) myosin and actin slide together because of the binding and contraction of actin filaments (c) tropomyosin wraps around myosin and blocks the binding sites between actin and myosin (d) Both (a) and (b).
80. Refer to the given figure and select the correct statement from the following. (a) A is a stalk that attaches ovule to the placenta. (b) B is mass of cells having abundant reserve food material. (c) C is female gametophyte formed from a megaspore through reduction division. (d) D represents basal part of the ovule. 81. Sweet potato is homologous to (a) Ginger (b) Turnip (c) Potato (d) Colocasia. 82. Which of the following statements about the "blender experiment" is not true? (a) The experiment preceded Watson's and Crick's elucidation of DNA structure. (b) Hershey and Chase used radioactive sulphur and phosphorus to follow the protein and nucleotides in their experiment. (c) They discovered that while different strains of bacteria have different percentage of nitrogen bases, the percent of adenine and the percent of thymine are equal, as are the percent of guanine and cytosine. (d) The experiment lent strong credence to the idea that DNA is the hereditary material, at least for viruses. 83. Identify different types of placentation and select the incorrect option.
(a) Type A placentation is found in marigold and sunflower (b) In type B plancentation, placenta forms a ridge along the ventral suture of the ovary (c) Type C placentation is present in Primrose, ovules are born on central axis. (d) In type D placentation, there is presence of false septum. 84. Fatty acids and glycerol are absorbed in (a) duodenum (b) ileum (c) jejunum (d) large intestine.
85. The given figure represents a single nephron from a mammalian kidney. Identify which of the labelled parts, match them with the functions (i-iv) and select the correct option. (i) The site of ultrafiltration. (ii) Particularly sensitive to ADH. (iii) The main site for the reabsorption of glucose and amino acids. (iv) Largely responsible for the maintenance of blood pH. (a) (i) - A, (ii) - E, (iii) - C, (iv) - D (b) (i) - A, (ii) - B, (iii) - C, (iii) - D (c) (i) - A, (ii) - B, (iii) - C, (iii) - E (d) (i) - A, (ii) - B, (iii) - D, (iii) - E 86. Joint X is a biaxial joint. It allows movement in two planes, back and forth and side to side. Select the option which gives the location of joint X. (a) Elbow and knee joint (b) Joints between carpals (c) Shoulder and hip joints (d) Joints between metacarpals and phalanges 87. The figures (A – D) show four animals. Select the correct option with respect to a common characteristic of two of these animals. (A)
(B)
(C)
(D)
(a) A and D respire mainly through body wall. (b) B and C show radial symmetry. (c) A and B have cnidoblasts for self-defence. (d) C and D have a true coelom. 88. During an injury nasal septum gets damaged and for its recovery which cartilage is preferred (a) elastic cartilage (b) hyaline cartilage (c) calcified cartilage (d) fibrous cartilage. 89. Non-cellular layer that connects inner surface of the epithelial tissue to the connective tissue is (a) basement membrane (b) epidermis (c) dermis (d) either (b) or (c). MT BIOLOGY
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90. Which one of the following statements about all the four of Spongilla, leech, dolphin and penguin is correct? (a) Penguin is homoiothermic while the remaining three are poikilothermic. (b) Leech is a fresh water form while all others are marine. (c) Spongilla has special collared cells called choanocytes, not found in the remaining three. (d) All are bilaterally symmetrical. 91. When a bacteriophage, in its lytic phase, carries some of the bacterium partially digested chromosome with it to another host cell, the process is called (a) generalised transduction (b) conjugation (c) transformation (d) specialised transduction. 92. The heart-shaped fern prothallus is (a) saprophyte (b) sporophyte (c) gamete (d) gametophyte. 93. The difference between alburnum and duramen is the presence in the former of (a) companion cell (b) living cells (c) raw cells (d) lignified cells. 94. A cell is equally permeable to sucrose solution & NaCl solution. First the cell is put in 0.6 M sucrose solution there is no change in size but when put in 0.6 M NaCl solution the size will (a) increase (b) decrease (c) remain same (d) can’t be said 95. Three of the following statements regarding cell organelles are correct while one is wrong. Which one is wrong? (a) Lysosomes are single membraned vesicles budded off from Golgi apparatus and contain digestive enzymes. (b) Endoplasmic reticulum consists of a network of membranous tubules and helps in transport, synthesis and secretion. (c) Leucoplasts are bound by two membranes, lack pigment but contain their own DNA and protein synthesizing machinery. (d) Sphaerosomes are single, membrane bound and are associated with synthesis and storage of lipids. 96. Emasculation is achieved by the removal of (a) entire gynoecium (b) stigma (c) anthers (d) petals and sepals. 97. Some criteria for classifying animals are I. Presence or a absence of coelom. II. Presence or absence of true tissue organisation. III. Presence of 2 or 3 tissue layers. 82
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The correct way of classification using the above criteria is (a)
(b)
(c)
(d)
98. Restriction enzymes present in several microorganisms cut foreign DNA at specific sites and destroy them. The enzymes do not destroy the cellular DNA because (a) the cellular DNA does not have the specific sites (b) the susceptible specific sites are masked by proteins (c) the restriction enzyme susceptible sites are modified by cellular enzymes (d) the restriction enzymes and DNA occupy different compartments. 99. A doctor advises a patient to include yellow fruits, carrots and butter in his diet. What deficiency disease do you think the patient is suffering from? (a) Night blindness (b) Colour blindness (c) Kwashiorkar disease (d) Marasmus disease 100. Drones in a colony of honey bee originate by (a) thelytoky (b) cyclic parthenogenesis (c) arrhenotoky (d) diploid parthenogenesis. Answer key 1. 6. 11. 16. 21. 26. 31. 36. 41. 46. 51. 56. 61. 66. 71. 76. 81. 86. 91. 96.
(b) (c) (d) (b) (d) (d) (a) (a) (b) (d) (d) (b) (d) (c) (d) (d) (b) (d) (a) (c)
2. 7. 12. 17. 22. 27. 32. 37. 42. 47. 52. 57. 62. 67. 72. 77. 82. 87. 92. 97.
(d) (c) (b) (c) (d) (b) (c) (a) (d) (a) (b) (d) (c) (d) (b) (b) (c) (d) (d) (d)
3. 8. 13. 18. 23. 28. 33. 38. 43. 48. 53. 58. 63. 68. 73. 78. 83. 88. 93. 98.
(b) (c) (d) (c) (c) (c) (c) (a) (c) (b) (b) (b) (b) (d) (c) (a) (b) (b) (b) (c)
4. 9. 14. 19. 24. 29. 34. 39. 44. 49. 54. 59. 64. 69. 74. 79. 84. 89. 94. 99.
(a) (b) (a) (d) (a) (d) (d) (a) (a) (a) (a) (b) (d) (d) (a) (a) (c) (a) (c) (a)
5. 10. 15. 20. 25. 30. 35. 40. 45. 50. 55. 60. 65. 70. 75. 80. 85. 90. 95. 100.
(d) (a) (d) (d) (a) (d) (a) (b) (a) (b) (c) (d) (b) (b) (a) (a) (a) (c) (c) (b)
nn
1.
The graph below shows changes in pressure in the heart and aorta during the course of a heartbeat.
(a) Pressure was recorded in three regions : left atrium, left ventricle and aorta. Which curves (G, H or I) represent these regions respectively?
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(b) In the graph, which period (labelled A, B, C or D) or point (labelled X, Y or Z), identifies each of the following: (i) Point when the atrio-ventricular valve closes is
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(ii) Point when the semi-lunar valve closes is
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Ventricular systole or contraction results in a rise of ventricular pressure, which on exceeding aortic pressure leads to emptying of ventricular blood into the pulmonary trunk and aorta.
As a result of ventricular systole, ventricular pressure rises above atrial pressure which leads to closing of both atrio-ventricular valves. As a result of ventricular diastole, the ventricular pressure falls below aortic pressure and then semi-lunar valves close. MT BIOLOGY
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(iii) Period when the ventricle is filling with blood is
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(iv) Period when the ventricle is emptying is
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(v) Period when the volume of the ventricle is not changing are
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(c) From the graph, estimate the diastolic arterial blood pressure that would be measured in an artery where it branches from the aorta.
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(d) From the graph, estimate the pumping pressure and resting pressure.
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(f) Which of the waves in electrocardiogram (P, Q, R, S and T) cause the atrial systole, ventricular systole and ventricular diastole?
2.
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During isovolumic contraction and relaxation.
After the aortic valve has closed, the pressure in the aorta decreases slowly throughout diastole because the blood stored in the distended arteries flows continually through the peripheral vessels back to the veins. Before the ventricle contracts again, the aortic pressure keeps falling.
Estimate systolic and diastolic pressures.
By counting the number of QRS complexes that occur in a given period, one can determine the heart beat rate of an individual.
ECG corresponds to a specific electrical activity of the heart.
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(g) Which heart sound (1st or 2nd) is associated with the closure of (i) bicuspid and tricuspid valves and (ii) semilunar valves?
During ventricular systole, the ventricular pressure rises and pushes the semilunar valves open.
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(e) Calculate the pulse rate in beats per minute.
About 80% of the blood flows directly through the atria into the ventricles even before the atria contract.
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When the ventricles contract, one hears the first heart sound and at the end of the contraction hears second heart sound.
Industrial production of insulin involves the following procedure : isolation of insulin mRNA from pancreatic cells, use of reverse transcriptase to prepare cDNA from the mRNA. cDNA is made into double-stranded DNA with the help of DNA polymerase. Then the double-stranded cDNA is inserted into the plasmid within the antibiotic resistance gene (selectable marker) and introduced into the bacteria where it codes for the product insulin. However, it is not as simple as it seems to be. There is difficulty in execution of the process since only some of the plasmids pick up and anneal to recombinant DNA fragments and only some of the bacterial cells subsequently take in the altered plasmids. The selective promotion of the growth of the bacteria that have acquired recombinant DNA is, thus, essential. MT BIOLOGY
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I. Study the given experimental set-up for selection and amplification of transformed bacterial cells.
(a) Which colony or colonies (1, 2, 3, 4 or 5) must be selected and amplified and why?
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(b) Which plate is suitable (A or B) for selecting the transformed bacteria and why?
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Antibiotic resistance gene acts as selectable marker. The transformed bacteria lose antibiotic resistance due to insertion of recombinant DNA.
In replica plating, a sterile pad is pressed on to plate A and then on to sterile agar in plate B.
II. Study the given experimental set-up to locate recombinant DNA with a labelled marker.
(c) What treatment 'X' is given to the replica of the master plate?
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(d) Why is this experiment performed when transformed bacterial cells were already selected?
A radioactively labelled gene probe hybridizes with complementary base sequence.
Vector may be or may not be altered with recombinant DNA.
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3.
In a population, only a person in 10,000 is albino. What will be the frequency of carriers of albinism in the population?
--------------------------------------------------------------------------------- ---------------------------------------------------------------------------------. 4.
Read the given passage and answer the questions that follow. There are three modes of natural selection operating on the populations. The first type, directional selection, favours one extreme of the distribution of inherited variability. The second type, stabilizing selection, favours in variance about that of existing mean and leads to a reduced mean. The third type, disruptive of selection, favours the extremes of variance.
The Hardy-Weinberg principle states that, in a large, randomly mating population, the gene and genotype frequencies remain constant (in the absence of migration, mutation and selection).
(a) Which type of natural selection would lead to speciation?
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I.
Analyze the given study on a moth population.
(b) Which type of natural selection is operating on the moth population?
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(c) Which type of natural selection leads to polymorphism?
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II. Analyze the given data on birth weight of babies born in a population.
(d) Which type of natural selection favours the pattern observed in the data?
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5.
The given graph illustrates the pattern of water uptake and loss by intact plants during a 24-hour period.
(a) For about how long in a 24-hour period did the plants lose water faster than they absorbed?
------------------------------------------------------------------------------------.
(b) What are the likely explanations for the slow-down in transpiration after 1400 hours?
Analyze the graph carefully.
Factors affecting transpiration rate.
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(c) What changes are expected if the plants are sprayed with abscisic acid before taking the readings?
Role of abscisic acid during water stress condition.
------------------------------------------------------------------------------------.
Refer to the graph given below and answer the questions that follow.
(d) What does the given graph illustrate?
------------------------------------------------------------------------------------.
(e) What is the likely explanation for this response ?
Response to water stress.
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(f) How can this study be useful for irrigation management?
Analyse the diurnal changes in the diameter of a tree.
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Compare it with conventional methods to measure plant water status.
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solutions 1. (b) (c) (d)
(e) (f)
(g)
2.
(b)
(c)
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(a) H, I and G (i) Y; (ii) X; (iii) D; (iv) B; (v) A and C. 80 mm Hg Pumping pressure - 120 mm Hg; Resting pressure 80 mm Hg. Pumping pressure is systolic pressure which is developed in arteries of the body during contraction of left ventricle which forcefully pours blood into aorta. Its value is maximum near the end of ventricular contraction when most of the ventricular blood has been pushed into arteries. Resting pressure is diastolic pressure in arteries of the body when left ventricle is in the state of getting filled (diastole) and is not pouring blood into arterial system. The interval between two successive QRS complexes is about 0.83 second. Therefore, the pulse rate is 60/0.83 times per minute or 72 beats per minute. The P wave is caused by spread of depolarization through atria, and this is followed by atrial contraction, which causes a slight rise in atrial pressure curve immediately afterwards. Next appears QRS waves, which form as a result of electrical depolarization of ventricles. This initiates contraction of the ventricles and causes ventricular pressure to rise. Finally, T wave is observed which represents the stage of repolarization of the ventricles. Therefore, the T wave occurs slightly before the end of ventricular contraction. When the ventricles contract, one first hears a sound caused by closure of the A-V valves. The vibration is low in pitch and relatively long-lasting and is known as the first heart sound. When the aortic and pulmonary valves close at the end of systole, one hears a rapid snap because these valves close rapidly, and the surroundings vibrate for a short period. This sound is called the second heart sound. (a) Bacterial colony 4 fails to grow on agar containing tetracycline and ampicillin and must therefore contain the inactive tetracycline resistance gene with the inserted DNA. These bacteria should be cloned and amplified. Plate 'A'. In replica plating, a sterile pad is pressed on to plate A and then on to sterile agar in plate B. In this way, the bacteria are transferred to the fresh plate and grow in exactly the same pattern as in A. This leaves plate A intact for selecting the transformed bacteria once they have been identified in plate B. If the sequence of basis in the recombinant gene is known (or if the amino acid sequence of the protein for which that gene codes is known), then it is MT BIOLOGY
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possible to make a gene probe ('marker') from the complementary bases, and use it to locate colonies of bacteria containing the recombinant gene. The process involves taking a replica of colonies growing on agar, breaking up the cells (lysis) and disposing of all contents except the DNA, which is treated to break the hydrogen bonds and expose its two strands. A radioactively labelled gene probe complementary to the base sequence of the recombinant gene is added and hybridised. The recombinant DNA can be hence, detected by autoradiography. (d) The first step helps to detect transformed bacteria i.e., bacteria which have antibiotic resistance gene inactivated due to insertion of recombinant DNA. The second step helps us to detect whether the selected (transformed) bacteria actually have recombinant DNA or not, i.e., if their acquired plasmids have recombinant DNA or not. Autoradiography locates such bacterial colonies. 3. Hardy-Weinberg principle states that in a large, randomly interbreeding population, the gene frequencies in a population remain stable and are constant from generation to generation. This is called genetic equilibrium where gene pool is constant and sum total of all the frequencies is 1. Hardy-Weinberg principle is represented using algebraic equations as following: p2 + 2pq+ q2 = 1 also, p + q = 1 where, p is frequency of dominant allele and q is frequency of recessive allele. Hence, p2 is the frequency of individuals in the population that are homozygotic dominant i.e., AA and q2 is the frequency of individuals in the population that are homozygotic recessive i.e., aa. 2pq represents frequency of individuals in the population that are heterozygotic or carriers. Now, we are given the data about individuals showing albinism. Albinism is an autosomal recessive disorder. Therefore, number of individuals with albinism is: q2 = 1/10000 or 0.0001 \ q = 0.0001 = 0.01 Now, p + q = 1 \ p = 1 – 0.01 = 0.99 Therefore, the frequency of carriers of albinism in the population i.e., 2pq, is 2 pq = 2 × 0.99 × 0.01 2 or, or 1/ 50 = 0.0198 0.02 100
4. (b)
(c)
(d)
5. (b)
(c)
(d)
(e)
Thus, in the given population, 1 person in every 50 individuals would be carrier of albinism. (a) Directional selection and disruptive selection may lead to speciation, whereas stabilizing selection can not. Directional selection is illustrated by the response of peppered moth population to polluted environment. This type of selection arises from a changing environment and results in a shift in the population mean for the selected character. This process results in the organism becoming adapted to a changed environment. Disruptive selection leads to divergence of the phenotype i.e., the emergence of two or more distinct phenotypes. It is the result of conditions that favour more than one phenotype within a population. The effect is to split the population into two subpopulations, leading to polymorphism. If gene flow between the sub-populations is prevented, then ultimately each population may give rise to a new species. This form of selection is rare but it is important as it underpins the origin of new species. This is stabilizing selection which favours the existing mean and leads to reduction in variance, i.e., variants are selected out. The graph illustrates that the death rates are higher for the lightest and heaviest birth weights of babies. It is evident that stabilizing selection favours a birth weight of 2.55 - 3.60 kg. (a) 8 hours At 1400 hours, the sunlight is mild, light affects transpiration indirectly. Stomata tend to be open in the light, and so transpiration is more likely to occur in the light than in the dark. Sunlight is also the chief source of heat energy for the plant and for evaporation. Transpirational rate is high at high temperature because it speeds up transpiration by providing the latent heat (enthalpy) of vaporization. At the same time high temperature also lowers the relative humidity of air. Both these changes increase the gradient in water vapour concentration between the substomatal cavity and the external atmosphere. Abscisic acid (ABA) is a growth inhibitor which triggers closure of stomata. Therefore, application of ABA on the plants (Ash and Sunflower) before taking the readings will reduce transpiration. The transpirational rate will decrease and subsequently absorption will decrease. The curves will show a fall. The given graph illustrates diurnal changes in the diameter of a tree over a seven-day period. There is a detectable shrinkage in the diameter of the trunk during the day which recovers during the night. Water flow in the soil, plant and atmosphere
continuum is driven by water potential gradients between each component of the system. Water moves from the soil to the roots and then up the tree in the xylem, which is considered to be bundles of hollow, dead cells. Surrounding the xylem are living cells, including cambial and phloem tissues. There are small flow paths between these living tissues and the xylem, but the connections are limited, causing resistances to flow that vary among tree species. As transpirational losses from leaves increase in the early morning hours, some water moves out of the living tissues and into the xylem in response to the water potential gradients that develop. Because the cell walls of the living tissues are flexible, this movement presumably causes the trunk to shrink. As transpiration slows in the late afternoon, the potential gradient reverses and some water flows back from the xylem to the living tissues, causing the trunks to swell. (f) Under deficit irrigation, transpiration during most of the day exceeds root water supply, and greater water potential gradients develop between the xylem and living tissue. The rate of water flow between these tissues then increases, causing greater trunk shrinkage. Trunk diameter fluctuations occur in response to the potential gradients within the trunk, which reflect the balance between tree water supply and demand. Therefore, there should be a close association between the daily evolution of tree water status and trunk diameter oscillations, which could be used instead of the conventional plant water status measurements for irrigation management. nn MU-OET (Manipal) 14th April-15th May (Online Test Booking System) AIPMT (Participating States/ 4th May Universities– Chattisgarh, Himachal Pradesh, Jharkhand Combined Entrance Competitive Exam Board, Madhya Pradesh, Manipur, Nagaland, Odisha, Punjab, Chandigarh, Medical Counselling Committee (DGHS), AFMC, Delhi University, Jamia Hamdard, BHU) Karnataka CET 1st and 2nd May COMEDK-UGET 11th May EAMCET 22nd May CMC-Vellore 23rd May AMU 27th May AIIMS 1st June JIPMER 8th June UP-CPMT 16th June MT BIOLOGY
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