SPM Biology Essays Collection
A compilation of biology essays from various sources for SPM. This is done for my revision, hope it helps you too :) ...
Yvonne Choo Shuen Lann November 28, 2009 Photosynthesis Light Reaction During the light reaction, chlorophyll captures light energy which excites the electrons of chlorophyll molecules to higher energy levels. In the excited state, the electrons leave the chlorophyll molecules. Light energy is also used to split the water molecules into hydrogen ions and hydroxyl ions. This reaction is known as the photolysis of water. 24H2O → 24H++ 24OH(light and chlorophyll)
The hydrogen ions then combine with the electrons released by the chlorophyll to form hydrogen atoms. 24H++24e-→24H The energy from the excited electrons is used to form energy-rich molecules of ATP. At the same time, each hydroxyl ion loses an electron to form a hydroxyl group. This electron is then received by the chlorophyll. 24OH-→24OH+24eThe hydroxyl groups then combine to form water and gaseous oxygen. 24OH→12H2O+6O2 Oxygen is released into the atmosphere and used for cellular respiration. The ATP molecules provide energy while the hydrogen atoms provide reducing power for the dark reaction which takes place in the stroma.
Dark Reaction The dark reaction is also known as the Calvin cycle. It is light independent. During the dark reaction, the hydrogen atoms are used to fix carbon dioxide in a series of reactions catalysed by photosynthetic enzymes. The overall reaction results in the reduction of carbon dioxide into glucose. 6CO2+24H→6(CH2O)+6H2O (CH2O) is a basic unit of glucose. Six units of it combine to form one molecule of glucose. The glucose monomers then undergo condensation to form starch which is temporarily stored as starch grains in the chloroplast. The entire process can be represented by the following equation. 6H2O+6CO2→C6H12O6+6O2
Yvonne Choo Shuen Lann November 28, 2009
Respiration Aerobic Respiration Aerobic respiration requires a continuous supply of oxygen from the air or water surrounding the organism. Oxygen that is taken in is delivered by the blood circulatory system to the body cells. In the cells, glucose molecules are oxidised by oxygen to release energy. Aerobic respiration can be summarised by the following chemical equation: C6H12O6+6O2→6CO2+6H2O+2898kJ Aerobic respiration involves the oxidation of glucose in the presence of oxygen to carbon dioxide, water and energy. Organisms that respire aerobically are called aerobic organisms. Aerobic respiration releases all the available energy stored within the glucose molecules. The entire process does not only involve a single chemical reaction, but also driven by a sequence of complex biochemical reactions which are catalysed by the respiratory enzymes. The energy stored within the glucose molecules are released gradually. This is far more useful to the organism than a sudden release of energy. Only a small portion of energy is lost in maintaining the body temperature. A larger portion of the energy is used to synthesise ATP from ADP and inorganic phosphate. ATP which is an instant source of energy is the main supply for all living cells. Each ATP molecule consists of three phosphate groups and the phosphate bonds can be easily broken down to release energy.
Anaerobic Respiration During vigorous exercise such as running a race, the muscles initially respire aerobically. However, the muscles soon used up all the available oxygen. In spite of the increased breathing rate and heartbeat rate, the blood cannot supply oxygen fast enough to meet their requirements. The rate at which oxygen is used by the muscles exceeds the amount of oxygen supplied by the blood. The muscles are in a state of oxygen deficiency, and an oxygen debt is incurred. As such, the muscles obtain extra energy from anaerobic respiration because oxygen is not available. During anaerobic respiration, the glucose molecules break down partially into an immediate substance called lactic acid instead of carbon dioxide and water. Because glucose is not completely broken down, the energy released during anaerobic respiration is much less than the energy released during aerobic respiration. In fact, for every molecule of glucose, anaerobic respiration releases only two molecules of ATP or 150kJ of energy per mole of glucose. In contrast, aerobic respiration generates 38 molecules of ATP or 2898kJ of energy per mole of glucose. Thus, in terms of energy yield, anaerobic respiration is less efficient than aerobic respiration. 2| Page
Yvonne Choo Shuen Lann November 28, 2009 Much of the energy is still trapped within the molecules of lactic acid. The accumulation of lactic acid can reach a high level of concentration which can cause muscle cramps and fatigue. This contributes to the exhaustion a person feels during and after a period of intense exercise. The person needs to breathe more deeply and rapidly in order to inhale more oxygen. The excess oxygen is used by the body to oxidise the accumulated lactic acid to carbon dioxide and water. Oxidation of lactic acid occurs mainly in the liver where a portion of it is oxidised to produce energy while the remaining ones is converted into glycogen for storage in the muscle cells. The oxygen debt is paid off when all the lactic acid is removed. This happens through the increased breathing rate after vigorous exercise. Therefore, an oxygen debt is the amount of oxygen needed to remove lactic acid from the muscle cells.
Digestion Ruminant When a cow feeds on grass, it partially chews the grass. This partially chewed food is swallowed into the rumen, the largest compartment of the stomach. Here, cellulose is broken down by the cellulose produced by symbiotic microorganisms such as bacteria and protozoa. Part of the breakdown products are absorbed by the bacteria and protozoa, the rest by the cow. As the food enters the reticulum, the cellulose undergoes further hydrolysis. The content of the reticulum, called the cud, is then regurgitated bit by bit into the mouth to be thoroughly chewed again. This process helps soften and break down cellulose, making it more accessible to further microbial action in other parts of the stomach. The cud is then re-swallowed and moves into the omasum. Here, large particles of food are broken down into smaller pieces by peristalsis. Water is removed from the cud. The food particles finally move into the abomasums, the true stomach of the cow. Here, gastric juices containing digestive enzymes complete the digestion of proteins and other food substances. The food then passes through the small intestine to be digested and absorbed in the normal way.
Rodents In rodents like squirrels, the caecum and appendix are enlarged to store the cellulose-producing bacteria. The breakdown products pass through the alimentary canal twice. The faeces in the first batch are usually produced at night and are soft and watery. Those are eaten again to enable the animals to absorb the products of bacterial breakdown as they pass through the alimentary canal for the second time. The second batch of faeces becomes drier and harder. 3| Page
Yvonne Choo Shuen Lann November 28, 2009 This adaptation allows squirrels to recover the nutrients initially loss with the faeces.
Colonisation and Succession Definition *Colonisation: is the process whereby living organisms move into a newly formed area which is devoid of life. *Succession: is the gradual process by which one community changed its environment so that it is replaced by another community. Mangrove Swamp The pioneer species of a mangrove swamp are the Sonneratia sp and Avicennia sp. The presence of these species gradually changes the physical environment of the habitat. The extensive root systems of these plants trap and collect sediments, including organic matters from decaying plant parts. As time passes, the soil becomes more compact and firm. This condition favours the growth of the Rhizophora sp. Gradually, the Rhizophora sp replaces the pioneer species. The seeds of the Rhizophora sp show distinct viviparity. The prop root system of the Rhizophora sp traps silt and mud, creating a firmer soil structure overtime. The ground becomes higher. As a result, the soil is drier because it is less submerged by sea water. The condition now becomes more suitable for another mangrove species, the Bruguiera sp, which replaces the Rhizophora sp. The buttress root system of the Bruguiera sp forms loops which extend from the soil to trap more silt and mud. As more sediment is deposited, the shore extends further to the sea. The old shore is now further away from the sea and is like terrestrial ground. Over time, terrestrial plants like the nipah palm and Pandanus sp begin to replace the Bruguiera sp. The gradual transition and succession from a mangrove swamp to a terrestrial forest and eventually to a tropical rainforest, which is a climax community, takes a long time. That is why we need to conserve and preserve our mangrove forest.
Pond Succession in a disused pond begins with the growth of pioneer species such as phytoplankton, algae and submerged plants like the Hydrilla sp, Cabomba sp and Elodea sp. These plants have special adaptive features which enable them to colonise the pond. Their fibrous roots penetrate deep into the soil to absorb nutrients and bind sand particles together. Plenty of sunlight penetrates through the clear water to allow photosynthesis to take place. When the pioneer species die and decompose, more organic nutrients are released into 4| Page
Yvonne Choo Shuen Lann November 28, 2009 the pond. The organic matter is converted into humus at the pond base. The humus and soil which erode from the sides of the pond are deposited on the base of the pond, making the pond shallower. The condition becomes more unfavourable for submerged plants but more suitable for floating plants such as duckweeds (Lemna sp), water hyacinths (Eichornia sp) and lotus plants (Nelumbium sp). These plants float freely on the surface of the water. Since these plants receive sunlight directly and can reproduce rapidly by vegetative propagation, they spread to cover a large area of the water surface and prevent sunlight from reaching the submerged plants. As a result, the submerged plants die because they cannot photosynthesise. The decomposed remains of the submerged plants add more organic matter on the base of the pond. At the same time, more erosion occurs at the edge which results in more sediments being deposited on the base of the pond. As a result, the pond becomes more and more shallow which makes it unsuitable for the floating plants. The floating plants are subsequently replaced by emergent (amphibious) plants which can live in water as well as on land, for example, sedges and cattails. The rhizomes of these plants grow horizontally across the habitat. Their extensive roots bind the soil particles together and penetrate deeply to absorb more mineral salts. These plants spread rapidly and colonise the habitat, changing it. The emergent plants grow from the edge of the pond towards the middle of the pond as the pond becomes shallower. When these plants die, their decomposed remains add to the sediments on the base of the pond. This further reduces the depth of the pond. The condition of the pond now becomes more favourable for land plants like small herbaceous weeds, for example, Ageratum conyzoides, Euphorbia hirta and Oldentandia dichotoma. As time passes, the land becomes drier and the pond dries up. Land plants such as shrubs, bushes and woody plants become more numerous. A primary forest emerges and eventually turns into a tropical rainforest which is also known as a climax community.
Cell Division Mitosis The two major phases mainly interphase and mitotic cell division also known as the M phase which consists of mitosis and cytokinesis begins and ends according to the cell cycle. Mitosis begins with interphase. Interphase is divided into three shorter stages, G1, S and G2. In G1 phase, the cell synthesises protein and new cytoplasmic organelles such as mitochondria and chloroplast. The chromosomes are not condensed and appear as thread-like structures called chromatin. In S phase, however, synthesis of DNA occurs. This means that the DNA in the nucleus undergoes replication. Each duplicated chromosome now consists of two identical sister chromatid which contain identical copies of the chromosomes DNA molecule. The cell continues to grow and remain metabolically active during G2 stage as a preparation for cell division. Interphase 5| Page
Yvonne Choo Shuen Lann November 28, 2009 is followed by the M phase which contains mitosis and cytokinesis. Mitosis can further subdivided into four phases mainly prophase, metaphase, anaphase and telophase. The mitosis in an animal cell begins with prophase. During prophase, the chromosomes in the nucleus condense and become more tightly coiled. The chromosomes appear shorter and thicker. Each chromosome now consists of a pair of sister chromatids joined together at the centromere. In the cytoplasm, spindle fibres begin to form and extend between the centrioles. Each pair of centrioles then migrates to lie at the opposite poles of the cell. The chromatids are attached to the fibres of the spindle by their centromeres. In most plant cell, the spindle fibre forms without the presence of centrioles. At the end of prophase, the nucleolus disappears and the nuclear membrane disintegrates. Metaphase begins when the centromeres of all the chromosomes are lined up on the metaphase plate, an imaginary plane across the middle of the cell. The mitotic spindles is now fully formed. The two sister chromatids are still attached to one another at the centromere. Metaphase ends when the centromeres divide. During anaphase, two sister chromatids of each chromosome separate at the centromere. The sister chromatids are pulled apart to the opposite poles by the shortening of the spindle fibres that connect the centromeres to the poles. Once separated, the chromatids are referred to as daughter chromosomes. By the end of anaphase, the two poles of the cell have completed and have equivalent sets of chromosomes. Telophase begins when the two sets of chromosomes reach the opposite poles of the cell. The chromosomes start to uncoil and revert to their extended state (chromatin). The chromosomes become less visible. The spindle fibres disappear and a new nuclear membrane forms around each set of chromosomes. The nucleolus also reforms in each nucleus; the process of mitosis is now completed. Cytokinesis, the division of the cytoplasm occurs towards the end of telophase. In animal cell, the actin filaments in cytoplasm contracts to pull a cleavage furrow. The cleavage furrow pinches at the equator of the cell and deepens progressively until the cell is separated into two daughter cells. Although plant cells undergo the same stages of mitosis as in animal cells, cytokinesis in plant cells us markedly different. A cleavage furrow does not form. Instead, membrane enclosed vesicles fuse to form a cell plate. The cell plate grows outwards until its edges fuse with the plasma membrane of the parent cell. New cell walls and plasma membranes are formed from the contents of the cell plate, which eventually divide the cell into two daughter cells. At the end of cytokineses, cellulose fibres are produces by the cell to strengthen the new cell walls. After cytokinesis, the new cells enter the G1 stage of interphase, thus completing the cell cycle. Each daughter cell contains diploid number of chromosomes.
Yvonne Choo Shuen Lann November 28, 2009 Meiosis only occurs in gametes which are reproductive cells. This is because meiosis is a reduction division of diploid cells to produce haploid sex gametes. Meiosis begins with a single duplication of chromosomes in the parent cells, followed by two cycles of nuclear and cell division mainly meiosis I and meiosis II. In meiosis I, basically, the chromosomes begin to condense. They become shorter, thicker and clearly visible. Unlike mitosis, the homologous chromosomes come together to form bivalents through a process called synapse. Each bivalent is visible under the microscope as a four-part structure called a tetrad. A tetrad consists of two homologous chromosomes, each made up of two sister chromatids. Non sister chromatids exchange segments of DNA in a process known as crossing over. Crossing over results in a new combination of genes on a chromosome. The points at which segments of chromatids cross over are called chiasmata. At the end of prophase I, the nucleolus and the nuclear membrane disappear. The two pairs of centrioles migrate to the opposite poles of the cells. Each pair of centrioles acts as a central point from which the spindle fibres radiate. In metaphase I, the chromosomes are lined up side by side as tetrads on the metaphase plate. The chromosomes are still in homologous pairs. The chromosome of each pair is attached to the spindle fibres from one pole while its homologue is attached to the fibre from the opposite pole. The centromere does not divide. During anaphase I, the spindle fibres pull the homologous chromosomes away from one another and move them to the opposite poles of the cell. Each chromosome still consists of two sister chromatids which move as a single unit. Although the cell started with four chromosomes, only two chromosomes move towards each pole. Next will be telophase I. The chromosomes arrive at the poles. Each pole now has haploid daughter nucleus because it contains only one set of chromosomes. The spindle fibres disappear. The nuclear membrane reappears to surround each set of chromosomes. The nucleolus then reappears in each nucleus. Cytokinesis usually occurs simultaneously with telophase I, resulting in two haploid daughter cells, and each receiving one chromosome from the homologous pair. Hence, another cell division is required as the chromosomes are still duplicated. Meiosis II follows immediately after cytokinesis, no interphase between them. DNA replication does not occur again and the chromosomes remained in a condensed state. In prophase II, the nuclear membrane of the daughter cells disintegrates again. The spindle fibres reform in each daughter cell. During metaphase II, the chromosomes each still make up of sister chromatids, are positioned randomly on the metaphase plate with the sister chromatids of each centromere pointing towards the opposite poles. Each sister chromatid is attached to the spindle fibres at the centromere. In anaphase II, however, the centromeres of the sister chromatids finally separated and the sister chromatids of each chromosome are now individual chromosomes. The chromosomes move towards the opposite poles of the cell. Lastly in telophase II, the nucleoli and the nuclear membrane reform. The spindle fibres break down. Cytokinesis follows 7| Page
Yvonne Choo Shuen Lann November 28, 2009 and four haploid daughter cells are formed, each containing half the number of chromosomes and is genetically different from the parent diploid cell. These haploid cells will develop into gametes.
Tissue Culture Technique A small piece of a plant’s leaf, shoot, bud, stem or root tissues are cut out. These cut out plants tissues are called explants. Alternatively, enzymes are used to digest the cell walls of tissues, for example, the mesophyll tissue from a leaf. This result in naked cells without cell walls called protoplasts. The explants or protoplasts are sterilised and then placed in a glass container which contains a nutrient solution with a fixed chemical composition. A culture medium or growth medium normally consists of a complex mixture of glucose, amino acids, minerals, and other substances required for the growth of the tissues. The culture medium and the apparatus used must be in a sterile condition and free from microorganisms which can contaminate the tissue culture. The pH and the temperature of the culture medium also need to be maintained at optimum levels. The explants or protoplasts begin to divide by mitosis. Cell division produces aggregates of cells. The aggregates of cells develop into a callus, an undifferentiated mass of tissue. The callus develops into a somatic embryo. The embryo develops into a plantlet which can later be transferred to the soil for growth into an adult plant. All the plantlets produced this way are genetically identical. Therefore, all the adult plants that develop from them share the same traits.
Cancer When a cell divides by mitosis repeatedly without control and regulation, it can produce cancer cells. Cancer is a disease caused by uncontrolled mitosis due to severe disruption to the mechanism that controls the cycle. Cancer cells divide freely and uncontrollably without heeding the cell cycle control system. Cancer cells compete with the surrounding normal cells to obtain sufficient nutrients and energy for their own growth. A cancer cell that is not destroyed will divide uncontrollably to form a tumour, an abnormal mass of cells. Cancer cells can intrude on and spread to other tissues which then lead to the malfunction of the tissues and ultimately death. Cancer can be caused by many factors such as damage to the DNA, changes in genes (mutation) that control cell division, ionising radiation, for example, Xrays, ultraviolet rays and gamma rays, certain chemical compounds like tar in tobacco smoke or carcinogenic (cancer-causing) compounds such as formaldehyde.
Yvonne Choo Shuen Lann November 28, 2009 Reproduction Menstrual Cycle Menstrual cycle is the monthly cycle of ovulation and menstruation. This cycle causes changes in the thickeninig of the endometrium or uterus wall every 28 days, beginning puberty until menopause. It is regulated by a few hormones mainly: –
Follicle stimulating Hormone (FSH) Produced by: Pituitary gland Function: Stimulates the development of follicles in the ovary Luteinising Hormone (LH) Produced by: Pituitary gland Function: Stimulates ovulation, the development of corpus luteum and promotes the secretion of progesterone Oestrogen Produced by: Follicle cells of the ovary Function: Stimulates further growth of the follicles, promotes the repair of the endometrium, from about the 12th day of the menstrual cycle, it has a positive feedback action on the secretion of the FSH and LH Progesterone Produced by: Corpus luteum Function: Stimulates the endometrium to become thick, folded and highly vascular (enriched with blood vessels) for the implantation of embryo; inhibits the secretion of FSH and LH to prevent the development of the graafian follicle and ovulation
Menstrual cycle involves two process mainly the breakdown of the endometrium and the formation of an ovum. On day 1-5, FSH stimulates the development of primary follicle to produce a Graafian follicle. FSH stimulates the follicle cells and ovary tissues to secrete oestrogen to heal and repait the uterus lining. This only takes place in the ovary. On the other hand, menstruation occurs in the uterus where blood is discharged from the vagina. This is when the uterus lining breakdown. On day 6-13, in the ovary, the graafian follicle matures. Oestrogen and progesterone level continue to increase. Till a certain point, the oestrogen will stop the pituitary gland from producing FSH and is stimulated to produce LH. In the uterus, the endometrium wall is repaired and thickens. On day 14, LH causes ovulation and the formation of corpus luteum from the follicle cells. In the uterus, however, the endometrium continues to thickens. On day 15-24, the corpus luteum develops and releases progesterone which stimulates the thickening of the endometrium. In the uterus, the endometrium becomes thicker and more blood vessels are present.
Yvonne Choo Shuen Lann November 28, 2009 On day 25-28, if there is no fertilisation, then there will not be any implantation. Thus, the corpus luteum degenerates causing the level of progesterone to decrease and halt. In the uterus, the endometrium begins to break down and menstruation occurs. The menstrual cycle continues. However, if fertilisation happens, a zygote will be implanted in the endometrium. The corpus luteum will continue to secrete oestrogen and progesterone until the placenta is formed to replace it. The presence of hormone progesterone inhibits the production of FSH and LH, this cause the menstrual cycle to stop during pregnancy.
Formation of Embryo Sac in the Ovule The ovule develops from the ovarian tissue. It has a diploid embryo sac mother cell (2n). Each ovule consists of protective outer layers of cells called the integuments. The embryo sac mother cell (2n) undergoes meiosis to form a row of four haploid cells called megaspores (n). Three of the four megaspores degenerate, leaving one in the ovule. The megaspore continues to grow and enlarges filling up most of the ovule. The nucleus of the three megaspores then undergoes mitosis three times to form eight haploid nuclei. Three of the eight nuclei migrate to one end of the cell to form antipodal cells. Another two nuclei, called the polar nuclei, move to the centre. One of the three nuclei nearest the opening of the ovule (micropyle) develops into an egg cell or female gamete, flanked by two synergid cells. The structure formed is known as the embryo sac. It is where the embryo will develop. The ovule, which eventually becomes a seed, now consists of the embryo sac and the surrounding integuments. *Eight cells have no cell walls; synergid cells provide nutrient and support to egg cell; integuments form protective layers around embryo sac.
Formation of Pollen Tube, Zygote and Triploid Nucleus Pollination is the process in which mature pollen grains from the anther are transferred to the stigma of a flower. A pollen grain on a stigma initiates the fertilisation process. The secretion of sucrose solution in the stigma stimulates the pollen grain to germinate and form a tube known as the pollen tube. The pollen tube grows through the tissues of the style into the ovule. During the growth of pollen tube, the generative nucleus divides by mitosis to form two male gamete nuclei. The male nuclei follow the tube nucleus down the pollen tube. When the pollen tube reaches the ovary, it penetrates the ovule through the micropyle. The tube nucleus disintegrates and the tip of the tube bursts, leaving the passage for the male nuclei to enter the embryo sac. Double fertilisation, which is unique for angiosperms, occurs within the ovule. This process involves the union of the two male gametes nuclei with different nuclei of the embryo sac. One male gamete nucleus fuses with the egg nucleus, forming a diploid zygote (2n). The other male gamete nucleus fuses with the two 10 | P a g e
Yvonne Choo Shuen Lann November 28, 2009 polar nuclei, forming a triploid nucleus (3n). The division of the tripod nucleus will give rise to the endosperm, the food-storing tissue of the seed. The synergid cells and the antipodal cell will degenerates.
The Lymphatic System Formation and Composition of Interstitial Fluid Blood that enters the arterial end of the capillaries is under high pressure. This is because the blood capillaries have a smaller diameter than the arterioles and arteries. This blood pressure causes fluid to leak continuously from the blood plasma into the spaces between the cells. This fluid is known as interstitial fluid. The interstitial fluid fills the spaces between the cells and constantly bathes the cells. The exchange of substances between the blood capillaries and the body cells occurs in the interstitial fluid. Nutrients and oxygen diffuses from the blood through the interstitial fluid into the body cells while carbon dioxide and other waste products diffuse from the body cells through the interstitial fluid into the blood. Interstitial fluid consists of water, dissolved nutrients, hormones, waste products, gases and small proteins from the blood. Leucocytes ooze through the openings in the capillary walls. Interstitial fluid does not contain plasma proteins (albumin, globulin and fibrinogen), erythrocytes and platelets because these are too large to pass through the capillary walls. About 85% of the fluid that leaves the blood at the arterial end of the capillary re-enters at the venous end. The interstitial fluid must be returned to the circulatory system to maintain the normal blood volume. About 15% of the fluid that is still remains in the interstitial space is equivalent to about 4 litres of fluid lost from the blood capillaries each day. The fluid loss is returned to the blood through the lymphatic system. *The higher BP at the arterial end forces fluid out of blood capillary; the lower BP at the venous end allows fluid to re-enter the blood capillaries.
Dynamic Ecosystem Nitrogen Cycle To build proteins, plants need the element nitrogen. The nitrogen gas in the atmosphere is about 78% but plants are not able to utilize the nitrogen. This is because the nitrogen has to be fixed before it can be absorbed by the plants. Nitrogen fixing bacteria (Nostoc sp, Azotobacter) which live in the root nodule of leguminous plant can convert nitrogen in the atmosphere into ammonia. Nitrosomonas converts/oxidises ammonia into nitrites. Nitrobacter oxidises/converts nitrites into nitrates. Nitrites and Nitrates can be absorbed by the plants as their nitrogen source. The plants protein is transferred to the
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Yvonne Choo Shuen Lann November 28, 2009 animals when consumed by the animals. The animals and plants proteins are transferred to human when consumed.
Blood Blood Clotting Mechanism Blood clotting mechanism involves a complex series of biochemical reactions in the blood to prevent excessive loss of blood after an injury. When you get a cut, the blood vessels around the wound immediately constrict to reduce blood loss. Exposed tissues, the collagens interact with the blood coagulation proteins to start the coagulation process. Platelets become activated as it begins to adhere to the wall of the blood vessel at the side of bleeding. They form a temporary platelet plug. The adhered platelets undergo degranulation and release cytoplasmic granules. The cytoplasmic granules attract more platelets to the area. While the platelets form the temporary plug, other blood proteins congregate on the damaged blood vessels to reinforce the clot. The interaction of the different blood clotting factors such as Factor VIII and platelets produces prothrombin. Prothrombin acts together with calcium ions and vitamin K to form an active plasma protein called thrombin. Thrombin transforms a protein called fibrinogen into fibrin. Fibrin surrounds the platelet plug, creating a fibrin mesh. The fibrin mesh is more stable than the temporary platelet plug. Over the next few days, the fibrin mesh or blood clot strengthens even more, protecting the blood vessels from further damage or blood loss. After the injury heals, the body has to remove the fibrin clot. A protein called plasmin is formed to dissolve fibrin. The blood clot is slowly removed with the help of plasmin.
Impaired Musculoskeletal System Muscle cramps A muscle cramp is a sudden contraction of one or more muscles which result in a sudden, intense pain and an inability to use the affected muscles. A muscle cramp is an involuntary, forcibly contracted muscle that is not able to relax. When the cramp begins, the spinal cord stimulates the muscle to keep contracting. The muscle groups usually affected are the back of the lower leg or the calf, the back of the thigh (hamstrings) or the front of the thigh (the quadriceps). A cramp can last from a few seconds to 15 minutes or more. Muscle cramps are very common among endurance athletes and older people who perform strenuous exercises. Usually, inadequate stretching and muscle fatigue lead to abnormalities in the mechanisms that control muscle contractions.
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Yvonne Choo Shuen Lann November 28, 2009 Muscular dystrophy is caused by the progressive degeneration and weakening of the skeletal muscles that control movement. The body muscles gradually become weak as they are replaced by fibrous tissue. This disease is caused by a mutated gene in the X chromosome and mainly affects boys. At present, there is no cure for muscular dystrophy.
Osteoporosis Osteoporosis is a common bone disorder which causes the bones to become thinner, more brittle and more porous. It is a common disease among elderly women. The loss of bone mass normally begins after the age of 30 years and accelerates greatly after the age of 45 years. It particularly affects women after menopause, when changes in hormone levels (especially oestrogen level) reduce bone strength. During the course of an individual’s life, the body needs phosphate and calcium to build bones. If the dietary intake of these minerals is not sufficient, or if the body does not absorb enough of these minerals from the diet, bone production and bone tissue will suffer, resulting in brittle and fragile bones. These bones are easily subjected to fracture. The loss of bone mass occurs gradually over an extended period of time. Most people are not even aware that they have osteoporosis until a bone is fractured because there are no symptoms or early signs of osteoporosis. Symptoms that manifest over the years include fractures of the vertebrae, wrists or hips; a reduction in height over time and a stooped posture. Osteoporosis can be prevented by taking adequate amounts of calcium, phosphorus and vitamin D. Regular exercise can also reduce the likelihood of bone fractures and help reduce bone mineral loss. Although there is no cure for osteoporosis, medications can slow down the loss of bone mineral.
Arthritis Arthritis refers to a group of skeletal disorders that involve inflammation of the joint. The joints become swollen, stiff and painful. One form of arthritis is osteoarthritis. Osteoarthritis is part of the ageing process caused by the wear and tear of the cartilage between the bones inside certain joints. The ageing process may also result in a decreased production of the synovial fluid in the joints. The patient usually suffers from a painful and stiff knee which restricts daily activities like walking and climbing stairs. If treatment fails to relieve pain, a surgeon can replace the damaged joints with artificial ones made of plastic or metal.
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Yvonne Choo Shuen Lann November 28, 2009
Respiration & Circulation Human Respiratory System During inhalation, the external intercostals muscles contract while the internal intercostals muscles relax. This action causes the ribcage to move upwards and outwards. At the same time, the diaphragm muscles contract. The diaphragm lowers and flattens. These two actions cause the volume of the thoracic cavity to increase, and the pressure of the thoracic cavity decreases. Higher atmospheric pressure on the outside forces the air to enter the lungs. During exhalation, the external intercostals muscles relax while the internal intercostals muscles contract. This action causes the rib cage to move downwards and inwards. At the same time, the diaphragm muscles relax. The diaphragm curves upwards (dome-shaped). These two actions cause the volume of the thoracic cavity to decrease, and the pressure of the thoracic cavity increases. Higher atmospheric pressure inside the lungs forces the ait out of the lungs.
Alveoli & Gaseous Exchange Gaseous exchange happens between the alveolus and the blood capillaries through diffusion. The oxygen concentration or partial pressure of oxygen, PO2 in the alveolus is higher than the blood capillaries. Blood capillaries carry carbon dioxide from body cells to the alveolus. So, it has a higher partial 14 | P a g e
Yvonne Choo Shuen Lann November 28, 2009 pressure of carbon dioxide, PCO2 compared to the air in the alveolus. Carbon dioxide diffuses into the alveolus and then it is breathed out through the nose or mouth. Oxygen diffuses into the blood capillaries from the lungs and combines with haemoglobin to form oxyhaemoglobin. Haemoglobin is the red pigment in RBC. Oxygen in the form of oxyhaemoglobin is carried to the cells and tissues. Oxyhaemoglobin is unstable so it will breakdown into haemoglobin and oxygen when it reaches the cell or tissue with lower PO2. Carbon dioxide is given out by cell as waste products of cellular respiration. This carbon dioxide is transported out of the cell by a few means. 7% of them dissolve in blood plasma, 23% of them binds with haemoglobin to form carbaminohaemoglobin, a type of multiple amino while 70% of them are carried with bicarbonate ions. CO2+H2O→H2CO3→H++HCO3*with the presence of carbonic anhydrase (HCO3)Blood plasma→lungs→nose (HCO3→CO2+H2O)
The Regulatory Mechanism of Carbon Dioxide Content in the Body During vigorous exercise, partial pressure of carbon dioxide increases as there is active cellular respiration. Carbon dioxide reacts with water to form carbonic acid. The higher carbon dioxide concentration level in the blood results in a drop in the pH value of the blood and tissue fluid (cerebrospinal fluid) bathing the brain. CO2+H2O→H++HCO3This drop of pH is detected by the receptors include the central chemoreceptors located in the medulla oblongata and the perisheral chemoreceptors which are sensitive to both the carbon dioxide content and the pH of the blood. The perispheral chemoreceptors are the aortic bodies found within the aortic bodies found within the aortic arch and the carotid bodies at the carotid arteries. Central and perispheral chemoreceptors send nerve impulses to the respiratory centre. The diaphragm and the intercostals muscles are the effectors in this case. When impulse reaches the effectors, the respiratory muscles contract and relax at a faster rate. As a result, the breathing rate and ventilation rate increase. As excess carbon dioxide is eliminated from the body, the carbon dioxide concentration and the pH value of the blood return to the normal level.
The Regulatory Mechanism of Oxygen Content in the Body The oxygen content in the blood usually has little effect on the breathing control centre. The perispheral chemoreceptors in the aortic bodies and the carotid bodies will only be stimulated if the oxygen level is very low, for example 15 | P a g e
Yvonne Choo Shuen Lann November 28, 2009 at very high altitudes. Usually a rise in the carbon dioxide concentration is a better indication of a drop in the oxygen concentration because both carbon dioxide and oxygen are involved in the same process, that is, cellular respiration. At high altitude, the decrease in concentration of oxygen in blood is detected by perispheral chemoreceptors. Nerve impulses are sent to the respiratory centre. This causes the diaphragm and intercostals muscles to contract and relax at a faster rate. Thus, breathing rate and ventilation rate increases so that more oxygen is inhale to make the concentration of oxygen in the blood to return to normal.
Rate of Respiration & the Gases content in Blood When an individual does an activity, the body cells require more energy. This causes the rate of respiration to increase. When PO2 decreases while PCO2 increases, the rate and depth of breathing also increases. The breathing rate increases will cause the increase of ventilation rate so that the rate of gaseous exchange between alveoli and blood capillaries increases. Lastly, the heartbeat rate increases causes more blood to be pumped into the circulation so that more oxygen can reach the cell to oxidise glucose for energy and also to remove the carbon dioxide from the cells to the air.
Compensation Point Compensation point is the light intensity at which the rate of carbon dioxide production during respiration is equal to the carbon dioxide consumption during photosynthesis.
Genetics Genetic Modification of Bacteria in the Mass Production of Insulin An enzyme is used to isolate and cut the bacterial plasmid. A plasmid is a circular DNA found in bacteria. The human gene that codes the production of insulin is isolated and inserted into the vector plasmid. An enzyme is used to incorporate the gene into the plasmid. The human gene together with the bacterial plasmid (called recombinant DNA) is inserted into the bacterial cell. The bacteria are cultured in a bioreactor. The plasmids are replicated as the bacteria divide asexually (producing clones) and make identical copies of themselves, all carrying the new gene that is capable of producing human insulin. The insulin produced in large quantities, purified and separated. This is a cost-effective way of producing sufficient amounts of insulin. 16 | P a g e
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Variation Comparison between Continuous &Discontinuous Variation i.
Similarities Both continuous and discontinuous variation creates varieties in the population of a species. Both variations are caused by environment factors or genetic factors or both. Variation that is caused by genetic factors can be inherited. This too can promote a higher survival rate in the formation of new species/individual.
Differences Continuous variation is a type of variation in which the differences in a character are not distinctive while discontinuous variation is a type of variation in which the differences in a character are distinctive. Height and weight are continuous variation as while blood group, fingerprint patterns, haemophilia and albinism are discontinuous variation. Continuous variation exhibits a spectrum of phenotypes with intermediate characters while discontinuous variation exhibits a few distinctive phenotypes with no intermediate characters. Continuous variation has characters that are quantitative, they can be measured and graded from one extreme to the other while discontinuous variation has characters that are qualitative, they cannot be measured or graded from one extreme to the other. Continuous variation is represented by a normal distribution while discontinuous variation is represented by a discrete distribution. Continuous variation is influenced by environmental factors while discontinuous variation is not influenced by environmental factors. Two or more genes control the same character for continuous variation while only a single gene determines the differences in the traits of a character. The phenotype of a continuous variation is usually controlled by many pairs of alleles while the phenotype of a discontinuous variation is controlled by a pair of alleles.
Genetic Variation in Sexual Reproduction Sexual reproduction, which involves the production and fertilisation of gametes, resulting in genetic variation in the offspring. There are three sources of genetic variation in sexual reproduction: i.
Crossing over during meiosis During prophase I of meiosis, when two homologous chromosomes are paired up in a bivalent, crossing over occurs between the chromatids. The exchange of genetic materials between the chromatids results in new,
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Yvonne Choo Shuen Lann November 28, 2009 different genetic combinations of genes from the parents. The new genetic combinations result in variation. ii.
Independent assortment during meiosis During metaphase I of meiosis, homologous chromosomes arrange themselves randomly at the metaphase plate. The random arrangement and separation of each homologous pair is independent of one another. Independent assortment produces various genetic combinations in the gametes. There are two equal possible arrangements of the chromosomes inherited from the parents. These variations in the arrangement of the chromosomes produce gamates with four equally possible combinations of the chromosomes.
Random fertilisation Each gamete has a unique set of combination of genes. A male gamete can fertilise any of the female gametes. The fertilisation between a male gamete and a female gamete occurs randomly. As a result, each zygote is unique. With random fertilisation, variations occur in the offspring.
Reproduction II Formation of Identical Twins Identical twins are formed when the ball of cells from a fertilised ovum splits into two embryos. Only one sperm and one ovum are involved in the process of fertilisation. The two embryos develop into two separate foetuses in the uterus. Each foetus has its own umbilical cord but shares the same placenta. Since the twins originate from one embryo, they are, therefore, identical in every aspect. They are born the same sex.
Formation of Fraternal Twins (Non-identical Twins) Fraternal twins are formed when two ova are released at the same time, one from each ovary. Each ovum is then fertilised by a sperm. As a result, two zygotes are formed and develop into two separate embryos. Each embryo has its own placenta and umbilical cord. They are genetically un-identical thus having different physique and may or may not varies in sex. Siamese Twins Siamese twins are identical twins which did not separate completely during embryonic development. Normally, Siamese twins are attached at certain parts of the body such as the head, chest, abdomen or hips. They may also share some common internal organs. Siamese twins can be separated surgically
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Yvonne Choo Shuen Lann November 28, 2009 and have a greater chance of survival if they do not share major internal organs like the heart, brain or lungs.
Development of a Zygote & Fertilisation During copulation, man ejaculates semen containing about 400 million sperms, into the woman’s vagina. The sperms swim up through the cervix into the uterus. After about 24 hours, 6000 sperms reach the fallopian tube. Half of the sperms die. After 30 hours, a few hundred sperms complete the journey. Ovulation occurs when a ripe egg/ matured ovum bursts from the ovary and is collected by the fallopian tube. Sperms surround the egg. Fertilisation occurs when one sperm penetrates the egg. The sperm’s nucleus fuses with the egg’s nucleus. 30 hours after fertilisation, the zygote divides to form two cells. More cell division takes place as the zygote moves along the Fallopian tube. From two cells, it slowly divides into four cells and so on to produce a solid ball of cells called morula. About 4 days after fertilisation, the embryo, now a hollow ball of about 128 cells (blastocyst), arrives in the uterus. It absorbs the nourishment which leaks out of the uterus lining. During the monthly cycle, oestrogen and progesterone produced by the ovaries cause the uterus lining to grow and thicken, ready to receive and nourish the embryo. Up to three days after its arrival in the uterus, the embryo sticks to the endometrium. Implantation happens. The embryo sinks into the endometrium and becomes buried by it. From the 9th week of development until birth, the embryo is called a foetus. After nine months of development inside the uterus, the baby is ready to be born.
Function of Placenta & Its Advantages Placenta takes over the job of corpus luteum to constantly produce oestrogen and progesterone to maintain the thick, blood-enriched endometrium throughout the pregnancy. The placenta is the site of the exchange of nutrients, respiratory gases and wastes between the foetus and its mother. The placenta is connected to the foetus by the umbilical cord. Umbilical cord is a tube with one umbilical vein and two umbilical arteries. The umbilical arteries carry deoxygenated blood from the foetus to the placenta while the umbilical vein carries oxygenated blood from the placenta to the foetus. Nutrients, oxygen, antibodies and hormones are transported through the umbilical vein from the maternal arteriole into the foetus. On the other hand, carbon dioxide and nitrogenous waste products are transported through the umbilical arteries from the foetus into the maternal vein. Placenta has many functions. It helps to synthesise glycogen, cholesterol and fatty acid. It is also a source of nutrients and energy for the developing embryo. Placenta not only secretes hormones like oestrogen and progesterone but it also secretes relaxin that can soften the cervix and relaxes the pelvic ligaments in
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Yvonne Choo Shuen Lann November 28, 2009 childbirth. It also produces protein hormone that is the human placental lactogen. This hormone prepares the breasts for lactation. Placenta forms a selective blood barrier that prevents the mixing of maternal and foetal blood. The two bloodstreams are separated by a thin membrane called blood barrier.
Birth Control Birth control can be done by various methods. There is the statistical method also known as the rhythm method. This control is natural as it estimates the period of fertility. The period is based on the length of past menstrual cycles. Another method called the barrier method is to wear condom (male & female) or diaphragm (female). This is done to prevent sexually transmitted diseases (STDs). Withdrawal method is another method where the penis is taken away from the female vagina right before ejaculation. There are drawbacks for this method as the semen might leak before ejaculation. Sterilisation can be done for both male and female for birth control. Vasectomy is done for male, where sperm duct is cut and tied while tubal ligation is done for female, where the fallopian tube is cut and tied. These methods can be done by surgery but they are irreversible. Intrauterine device (IUD) can be used for birth control. IUD is inserted into the uterus so that it interrupts the normal uterine environment and prevents the implantation of zygote in the endometrium. The T-shaped IUD is made up of copper and plastics. Another method known as the hormone method can too be used for birth control. This can be done by taking contraceptive pills orally. These pills contain a combination of oestrogen (increases weight) and progesterone. Ovulation is prevented by inhibiting the secretion of FSH and LH. This is because a high level of oestrogen and progesterone inhibits the pituitary gland from secreting FSH and LH. Lastly there is the awareness method. This is done by analysing the temperature of the uterus lining by plotting temperature graphs (also known as the basal body temperature). Sexual intercourse in the period where the basal body temperature is high is prevented as high basal body temperature give a sign that the process of ovulation is happening on that particular day.
Technology in aid of Infertility Infertility will not be a problem as the technology improves. This is because there are many methods that can aid infertility in both men and women. Artificial Insemination (Intro-uterine insemination) can be used for male that has low sperm count. This is done by collecting the man’s sperm over a period of time so that the sperm count will be high enough for fertilisation. The wife can be inseminated with the husband’s sperms or sperms from the sperm bank. The sperms are injected directly into the fallopian tube. Sometimes, the 20 | P a g e
Yvonne Choo Shuen Lann November 28, 2009 woman is inseminated with sperms obtained from the sperm bank. A sperm bank is a special laboratory that stores sperms in liquid nitrogen at a temperature of -196oC. Sperms from the donors are collected, frozen and kept in a sperm bank. The genetic biodata of each donor are kept meticulously, so that a woman wishing to conceive can use the sperm bank to obtain the sperms she wants. In some cases, another woman can be used as a surrogate mother as some females are unable to give birth or even to get pregnant. The sperms and ova are contributed by the parents. The sperms can also be obtained from a sperm bank and the ova from the surrogate mother. Either sperms or an embryo is transferred to the uterus of the surrogate mother. The surrogate mother then becomes pregnant and the foetus develops in her uterus until birth. In vitro fertilisation, another method of fertilisation that occurs in a controlled environment of a laboratory outside the human body. This method is used when the fallopian tubes are blocked, thus preventing fertilisation by the sperms. A fine laparoscope is used to remove mature ova from the ovary. The ova are then placed in glassware with culture solution to mature. Then, concentrated sperms from the father are added. The sperms and ova fuse and develop into embryos. After two to four days, when the embryos are selected and inserted into the uterus through the cervix for implantation on the uterine wall. If the procedure is successful, the implantation embryos will develop into a healthy baby or healthy babies. Babies conceived in this method are sometimes called test-tube babies. Couples can also use ova from donors.
Spermatogenesis Spermatogenesis occurs in the germinal epithelium of the seminiferous tubules. The primodial germ cell in the germinal epithelium cells (2n) divides by mitosis to produce spermatogonia (2n) (spermatogonium sing.). One spermatogonium (2n) grows in size to become a primary spermatocyte (2n). Each primary spermatocyte (2n) undergoes meiosis I to produce two secondary spermatocytes. Each secondary spermatocyte (n) completes meiosis II to produce spermatids (n). In the process of spermiogenesis, each spermatid differentiates (matures) into a spermatozoa/sperm (spermatozoon sing.).
Oogenesis Oogenesis occurs in the germinal epithelium of the ovary before birth and is regulated by hormones. The primodial germ cell in the germinal epithelium cells (2n) divide by mitosis to produce oogonia (2n) (oogonium sing.). The oogonium (2n) grows in size to become a primary oocyte (2n). Each primary oocyte (2n) undergoes meiosis but stops at prophase I of meiosis I. Meiosis resumes at puberty to produce a larger secondary oocyte (n) and a smaller first polar body. The secondary oocyte (n) undergoes meiosis II and stops at metaphase II. The first polar body completes meiosis II to form two polar bodies 21 | P a g e
Yvonne Choo Shuen Lann November 28, 2009 (n). At this stage, the secondary oocyte, together with the layers of follicle sells around it, is now called a secondary follicle. The secondary oocyte starts to grow in the follicle. The secondary follicle increases in size and matures to form the graafian follicle. At intervals of approximately 28 days, the graafian follicle merges with the wall of the ovary. The ovarian wall and the graafian follicle then rupture, releasing the secondary oocyte or egg into the fallopian tube. This process is known as ovulation. If the secondary oocyte is fertilised by a sperm, meiosis II will be completed to form two haploid cells of unequal size. The larger cell is ovum while the other is a polar body. The nuclei of the sperm cell and the ovum then fuse to form a diploid zygote (2n). This means a primary oocyte ultimately give rise to a single haploid ovum and three haploid polar bodies. All polar bodies will degenerates. After ovulation, the follicle cells left in the ovary form a corpus luteum. If there is no fertilisation, the corpus luteum will degenerates after a few days. The cycle formation of the graafian follicle, ovulation and the corpus luteum is known as the ovarian cycle. Actions Voluntary Actions of the Skeletal Muscles Voluntary actions such as walking and talking are under conscious control. Voluntary control of the skeletal muscles is governed by the cerebral cortex of the cerebrum. The pathway of the transmission in voluntary actions is as follows. When the door bell rings, the receptors in the ear pick up the ringing of the doorbell. The receptors trigger nerve impulses in the afferent neurones. The nerve impulses pass from the afferent neurones to the interneurones in the brain. The brain interprets the nerve impulses from many interneurones that the doorbell is ringing. The brain also decides that the door should be opened. From the interneurones, nerve impulses are transmitted to the efferent neurones and then to the muscles. The muscles in the arm carry out the response and open the door.
Involuntary Actions of the Skeletal Muscles: The Reflex Arc Involuntary actions that involve skeletal muscles allow an immediate action that does not require conscious effort. In such circumstances when the responses to stimuli are involuntary, they are called reflexes. A sharp pin pierces the skin causing the sensory receptors in the skin to generate impulses. The nerve impulses are transmitted along an afferent neurone towards the spinal cord. In the spinal cord, the nerve impulses are transmitted from the afferent neurone to an interneurone. From the interneurone, the nerve impulses are transmitted to an efferent neurone. The efferent neurone carries the nerve impulses from the spinal cord to the effectors (muscle tissue) so that the pin can be pulled out from the skin immediately.
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Yvonne Choo Shuen Lann November 28, 2009 Special Case: Knee-jerk (patellar reflex) Knee-jerk only involves the simplest neural circuit because it involves only two kinds of neurones: the afferent neurone and the efferent neurone. The reflex hammer hits a tendon that connects the quadriceps muscle in the thigh to a bone in the lower leg. As the hammer strikes the knee, the force stretches the quadriceps muscles and stimulates the stretch receptors in the muscles, triggering nerve impulses. Afferent neurones transmit the information to the efferent neurones in the spinal cord. The efferent neurones transmit this information to the quadriceps muscles, and the muscle contracts, jerking the leg forward.
Synapses The transmission of information is by no means electrical but chemical in nature. When the nerve impulse reaches the end of the presynaptic end of the neurone, it will stimulate the release of chemicals named neurotransmitters in the synaptic vesicles. The synaptic vesicles then fuse with the cell membrane, releasing the neurotransmitters through exocytosis. The neurotransmitters then cross the synapse where they may be accepted by the next neurone at a specialised site called a receptor. The neurotransmitters then fuse with the receptor thus transmitting the nerve impulse to the next neurone. Vesicles containing the neurotransmitters are only in the presynaptic end and the receptors are only on the postsynaptic end, therefore the synapse ensures that the flow of impulses in one direction only.
Diseases Related to Nervous System i.
Alzheimer’s Disease Neurological disease characterised by increasing loss of memory and intellectual ability. It is associated with the shrinkage of brain tissues and lack of neurotransmitters such as acetylcholine. Alzheimer usually affects elderly. Patient with it will show loss of intelligence, loss of memory, mild confusion and poor concentration. This disease can be inherited.
Parkinson’s Disease Parkinson’s disease is a chronic disease of the nervous system. It causes tremors and weakness of the muscles. This is due to the reduced level of neurotransmitters called dopamine in the brain. In some cases, the disease is caused by the hardening of the cerebral arteries. This causes muscles not functioning smoothly and becomes stiff and jerky in their actions. This disease affects elderly but is not a heredity disease. Levodopa is administered in the treatment of this disease.
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Hormone imbalanced i.
Growth Hormone Over secretion of the growth hormone during childhood results in gigantism, a condition characterised by an abnormal increase in the length of bones. The person grows to be abnormally tall. Over secretion during adulthood results in acromegaly, a condition in which the bones, hands, feet, cheeks and jaws thicken, and other tissue enlarges. Under secretion during growing years retards bone growth, resulting in a condition known as dwarfism. The organs of the person often fail to grow and the size of the body is like that of a child. Today, genetically engineered growth hormones can be given to children with the deficiency in growth hormone and successfully induce growth, allowing the children to attain normal height.
Thyroxine Over secretion causes an increase in the metabolic rate of the body. Common symptoms include excessive sweating, heat intolerance, increased bowel movements, nervousness, rapid heart rate and weight loss. Sometimes, the thyroid gland can grow and enlarges two or three times its normal size, a condition known as goitre. One causes of goitre is iodine deficiency. In this situation, the thyroid gland cannot synthesise and release enough thyroxine (throxine contains iodine). As a result, it enlarges in response to excess stimulation from the pituitary gland. Under secretion during childhood can cause severe mental retardation, a condition known as cretinism. In adulthood, it causes myxedema. A person with myxedema has a slow heart rate, low body temperature, high sensitivity to cold, general lethargy and a tendency to gain weight easily. A lack of iodine in the diet also reduces the production of thyroxine.
Insulin Over secretion of insulin can lead to hypoglycaemia, an abnormally low level of glucose in the blood. Some of the symptoms of hypoglycaemia are fatigue, insomnia, mental confusion, nervousness, mood swings, fainting spells and headache. Severe hypoglycaemia can lead to convulsions and unconsciousness. Under secretion of insulin can lead to diabetes mellitus. Diabetes mellitus is a chronic condition associated with abnormally high levels of sugar (glucose) in the blood. People with diabetes either do not produce enough insulin or cannot use the insulin that their body produce. As a result, glucose builds up in the bloodstream. A person with diabetes mellitus experiences an increase in frequency of urination, excessive thirst,
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Yvonne Choo Shuen Lann November 28, 2009 numbness or burning sensation in the feet, ankles and legs, blurred or poor vision, fatigue, and slow healing of wounds. Large quantities of human insulin are now produced by genetically engineered bacteria. Patients are usually injected with this commercially prepared insulin. iv.
Antidiuretic hormone (ADH) Over secretion of ADH can results in high retention of water in the body. Under secretion of ADH can result in a disorder known as diabetes insipidus. As a result, the person excretes a large amount of urine. People with diabetes insipidus are thirsty all the time. They often want to drink liquids frequently. This is because so much water is lost in the urine; the person may die of dehydration if deprived of water for even a day.
Kidney & Its Function + the Formation of Urine Kidney is situated in the dorsal wall of the abdomen. It has three main parts that are the outer cortex, inner medulla and the pelvis. Each kidney consists of numerous tubular units that are called nephrons. Kidney is needed to remove toxic waste products from our body. Kidney involved in the osmoregulation to keep the osmotic concentration of the blood constant by removing excess water and salts. It regulates the pH of the blood by controlling the removal of hydrogen ions. It also controls the blood volume. The formation of urine depends on the nephrones through three processes:
Ultra filtration The afferent arteriole which has a bigger diameter than that of the efferent arteriole sends blood to the glomerulus. The blood is now under relatively high pressure and ultra filtration takes place in the Bowman’s capsule. The filtrate which filters into the Bowman’s capsule consists of small molecules, water, glucose, amino acids, urea and mineral salts. The filtrate does not contain blood cells or plasma proteins. These components remain in the glomerular capillaries as they are too large. The filtrate then goes down the proximal convoluted tubule for reabsorption.
Reabsorption Reabsorption takes place in the proximal convoluted tubule, loop of Henle, distal convoluted tubule and collecting duct. At the proximal convoluted tubule, about 65% of the water in the glomerular filtrate (water, urea, glucose, amino acids and salts such as sodium ions) is absorbed back into the surrounding blood capillaries by osmosis. All the glucose, amino acids, vitamins and some salts are reabsorbed by active
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Yvonne Choo Shuen Lann November 28, 2009 transport. Urea is not reabsorbed. As the filtrate (water, salt and urea) passes along the loop of Henle, about 20% of the water and some salts are reabsorbed into the blood capillaries. At the distal convoluted tubule and collecting duct, the amount of water and salts that are reabsorbed into the blood capillaries depends on the content of water and salt in the blood. Reabsorption of water and salts is regulated by the endocrine system. iii.
Secretion Secretion takes place in the distal convoluted tubule. Along the tubule, waste products such as urea, uric acid and ammonia are pumped out of the blood capillaries into the distal convoluted tubule by active transport. This process is called secretion. Some drugs and toxic substances are secreted by simple diffusion. The final glomerular filtrate which remains in the collecting duct is called urine (96% of water, 2.5% nitrogenous products such as urea, uric acid, ammonia and cretinine, 1.5% salts and other trace elements such as bile pigments). From the collecting ducts, urine is channelled into the pelvis and carried out of the kidney by the ureter to the urinary bladder before it is excreted through the urethra.
Homeostasis Homeostasis is the regulation of the physical and chemical factors in the internal environment to maintain a constant internal environment.
Osmoregulation Osmoregulation is the regulation of salt and water balance in the body to maintain the blood osmotic pressure. It is controlled by two hormones mainly Antidiuretic Hormone (ADH) and aldosterone. When the osmotic pressure increases, it is detected by the osmoreceptors in the hypothalamus. Nerve impulses are sent to the pituitary gland so that more ADH and less aldosterone is secreted. This causes the distal convoluted tubule to become more permeable to water and impermeable to salt. More water and less salt then moves into the distal convoluted tubule through diffusion. The osmotic pressure declines back to normal. When the osmotic pressure decreases, it is detected by the osmoreceptors in the hypothalamus. Nerve impulses are sent to the pituitary gland so that more aldosterone and less ADH is secreted. This causes the distal convoluted tubule to become more permeable to salt and impermeable to water. Less water and more salt then moves into the distal convoluted tubule through diffusion. The osmotic pressure increases back to normal.
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Yvonne Choo Shuen Lann November 28, 2009
Glucoregulation The normal blood glucose level is 90mg in 100cm 3 of blood. When the blood glucose level increases, the change is detected by the β-cells of the Islets of Longerhans. This stimulates the pancreas to secrete insulin. Glucose is converted into glycogen for temporal storage. Glycogen is converted into lipid to be stored under the adipose tissues. Part of the glucose is used as the respiration of glucose increases. The blood glucose level declines back to normal. When the blood glucose level decreases, the change is detected by the α-cells of the Islets of Longerhans. This stimulates the pancreas to secrete glucagon. Lipid is converted back to glycogen while glycogen is converted back to glucose. The blood glucose level rises back to normal.
Thermoregulation Thermoregulation is the regulation of body temperature. When the body temperature increases to a value higher than 37oC, it is detected by the thermoreceptors in the hypothalamus. Nerve impulses are sent to the hypothalamus. The hair erector muscles relax to lower the hair so that no air is trap on the surface of the skin. Sweat gland is activated to produce sweat. This is to allow heat loss by means of evaporation. Muscle activities are also reduced to minimise heat production. Vasodilation occurs when smooth muscles of blood capillaries dilate so that more heat can be released through radiation. Adrenal gland secretes less adrenaline while thyroid gland secretes less thyroxine to lower down the rate of metabolism. The body temperature declines back to normal. When the body temperature decreases, it is detected by the thermoreceptors in the hypothalamus. Nerve impulses are sent to the hypothalamus. The hair erector muscles contract to raise hair so that more heat is trapped on the skin surface. Sweat gland is inactive to stop sweat so no heat loss via evaporation. Voluntary muscular activity is increased such as rubbing the hands to keep warm while involuntary muscles contract and relax frequently leading to shivering to produce heat. Vasoconstriction occurs when smooth muscles of the blood capillaries constrict to lower down heat loss. Adrenal gland secretes more adrenaline while thyroid gland secretes more thyroxine to increase the rate of metabolism. The body temperature rises back to normal. Auxin & Its Effects on the Growth of Plants Plants hormones are organic compounds that act as messengers that promote or inhibit plant growth and development. Some examples of it are auxin, gibberellins, cytokinin, abscisic acid and ethylene (a gas). Auxin stimulates cell tropism. Auxins are continuously produced by the meristematic 27 | P a g e
Yvonne Choo Shuen Lann November 28, 2009 cells of the shoot tip. It is then transported to the shoot via the phloem. Therefore, they are highest in concentration in the shoot tip and lowest at the root tip. The concentration of auxins in the shoot tip and the root tip affects growth. High concentration of auxin in shoot promotes elongation of cells. Hence the lower side of the shoot with a higher concentration of auxins will grow faster than the upper side. As a result, the shoot curves upwards, showing negative geotropism. A high concentration of auxins inhibits the elongation of cells in the root. The upper side of the root grows faster than the lower side. The young root curves and grows downwards, showing positive geotropism. Auxins move away from the light, accumulate in the shaded side.
Locomotion Antagonistic Muscles Antagonistic muscles are a pair of muscles which work together to allow coordinated movements of the skeletal joints. This means that when one muscle contracts, the other relaxes.
Bending & Straightening of the Arm When the biceps contract, the triceps relaxes. The biceps becomes shorter and thicker while the triceps becomes longer and thinner. This exerts a pulling force transmitted to the radius through the tendons. As a result, the radius is pulled upward and the arm is bended. The elastic ligaments that held the radius, ulna and the humerus together enable the radius and ulna to be pulled upward, bending the arms from the elbow. When the triceps contract, the biceps relaxes. Now, the triceps becomes shorter and thicker while the biceps becomes longer and thinner. The triceps that contracts exert a pulling force on the ulna through its tendon. The ulna and radius, which are jointed to the humerus by the elastic ligaments, is pulled together downwards, causing the arm to straighten.
Walking The calf muscle contracts and raises the heel. In doing so, it exerts a forward thrust by pushing the ball of the foot against the ground. The hamstring muscle contracts to pull the femur back and bends the knee. The leg is raised. As the right foot loses contact with the ground, the weight of the body is now supported by the left leg which is still in contact with the ground. Next, the quadriceps muscle contracts, pulls the femur forward and extends the leg. When the extension of the leg is completed, the foot then regains contact with the ground with the heel touching the ground first. The weight of the body is now supported on the right leg. The whole sequence is repeated with the left leg.
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Yvonne Choo Shuen Lann November 28, 2009 Worm The movement of earthworm is carried out by a series of contraction and relaxation of both the circular and longitudinal muscles of its body. When the circular muscle at the anterior contracts, the longitudinal muscles relaxes. The body becomes thinner and lengthens. The body fluid is pushed to the posterior part of the body. When the longitudinal muscle at the anterior contracts and the circular muscle relax, the body flatten and shortens. The body fluid will be pushed to the front part by hydrostatic pressure and the posterior will be pulled forward. Each segment has chaetae which help to anchor the worm during locomotion and pull itself forward. The antagonistic muscles working in opposite directions produce hydrostatic pressure of the body fluid. Thus, creating peristalsis wave.
Fish The movement of tail is caused by the contraction and relaxation of the myotome muscles on both side of the body. The contraction of the muscle on the right side will pull the tail to the right whereas the contraction of the muscles on the left side will pull the tail to the left. The continuous movement of the tail from left to the right will create a push for the fish to move forward. The function of the fins help in controlling the direction as well as the stability of fish in the water.
Bird The antagonistic actions of the strong muscles enable the bird to flap its wings up and down. When the pectorial major (in) contracts and the pectorial minor (out) relax, the wings flapped downwards. When the pectorial minor (out) contracts and the pectorial major (in) relaxes, the wings goes up.
Grasshopper & Frog Grasshopper has strong muscular hind legs that are the flexor (in) and the extensor (out) muscle to enable them to jump. A flexor muscle controls forward leg movement while the extensor controls the backward movement. Before jumping, the hind leg is folded in the shape of alphabet Z, the flexor muscle contracts while the extensor relaxes. When the extensor muscle contracts and the flexor muscle relax, the hind leg will straighten quickly resulting in a lift and the grasshopper jumps forward and upward. To land, the forelegs are extended forward to absorb the landing shock. The hind legs are then folded again. For walking, the grasshopper uses three legs to move while the other three labelled X are used to support the body. 29 | P a g e
Yvonne Choo Shuen Lann November 28, 2009 Frog has locomotion almost identical to grasshopper. It also has long, big and strong muscular hind legs. The contraction of the femur muscles result in straightening of the leg quickly. The feet push the ground causing the frog to jump upward and outward. During landing, the front legs are extended first to absorb the landing shock. At the same time, the hind legs are folded again into its Z shape. Respiration II Fish When a fish inhales, its mouth opens and the buccal cavity is lowered. As this occurs, the operculum closes and the opercular cavity becomes bigger. This resulted into a lower pressure in the buccal cavity. Water is then drowned into its mouth along with dissolved oxygen. When a fish exhales, its mouth closes, raising the floor of the buccal cavity. A water flows through the lamellae, respiratory gases are exchanged between blood capillaries and water. As this occurs, the opercular cavity becomes smaller. The high pressure in the buccal cavity forces the operculum to open allowing water to flow out.
Grasshopper Insects inhale and exhale through the rhythmic contraction and expansion of their abdominal muscles. The body movements and the contractions of the abdominal muscles speed up the rate of diffusion of gases from the tracheae into the body cells. When an insect inhales, the abdominal muscles relax and the spiracles open. Air pressure inside the tracheae decreases and air is drawn in. When an insect exhales, the abdominal muscles contract. The increased air pressure forces air out through the spiracles. The spiracle system with its network of small tubes allows oxygen to be absorbed directly from the atmosphere into the body cells. Therefore, there is no circulatory system in insects.
Frog When a frog inhales, it breathes in through its nostrils. The buccopharyngeal floor is lowered and fresh air is drawn in. At the same time, its glottis closes and state air remains in the lungs. Afterwards, the glottis will open. Its nostrils are then closed and the bucco-pharyngeal floor is raised. This causes high air pressure which forces air into its lungs thus, expanding them. When a frog exhales, its lung muscles contract, expelling air from its lungs. A frog does this by the abdominal pressure and elasticity of the lungs. Some of the 30 | P a g e
Yvonne Choo Shuen Lann November 28, 2009 air flows out of its nostrils and some mixed with the air in the bucco-pharyngeal cavity. *Filling in air: nostrils open, glottis closed, floor of the mouth lowers *Force air in: nostrils closed, glottis open, floor of the mouth rises *Expiration: nostrils open, glottis open, lung contracts
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