Forest Botany For Forestry Students

 

 

Forest Botany Unit 5 and 6

 

CELL STRUCUTRE AND PLANT TISSUES

The cell  is the basic structural structural,, functional functional,, and biological biological unit of all known living organisms. organisms. A cell is the smallest unit of life life.. Cells are often called the "building blocks of life". The study of  cells is called cell biology. Cells are of two types: Cells types: eukaryotic, eukaryotic, which which co cont ntai ain n a nucleus, nucleus, and and  prokaryotic,  prokaryotic, which do not. Prok Prokar aryo yote tess are are single-cel single-celled led organisms organisms,, whil whilee eu euka kary ryot otes es ca can n be ei eith ther er si sing ngle le-c -cel elle led d or  multicellular . Sub cellular components

eukaryotic, have have a membrane that membrane that envelops the cell, regulates All cells, whether prokaryotic whether  prokaryotic   or eukaryotic, what moves in and out (selectively permeable), and maintains the electric potential of the cell. cell . Inside the membrane, the cytoplasm takes cytoplasm takes up most of the cell's volume. In cell biology biology,, the cytoplasm is all of the material within a cell, cell, enclosed by the cell membrane membrane,, except for the except the cell nucleus. nucleus. The material material inside inside the nucleus nucleus and contained contained within within the nuclear  membrane is membrane  is termed the nucleoplasm. nucleoplasm. The main components of the cytoplasm are cytosol  cytosol  – a gel-like gel-l ike substance, substance, the organelles  organelles  – the cell's internal internal sub-structure sub-structures, s, and various various cytoplasmic [1] inclusions.. The cytoplasm is about 80% water and usually colorless. inclusions Protoplasm  is the living content of a cell that cell that is surrounded by a plasma a plasma membrane

a biological term  term proposed by Hanstein in Hanstein in 1880 to refer to the entire cell, excluding Protoplast is a biological the cell wall. The cytosol, also known as intracellular fluid ( ICF) or cytoplasmic matrix is the liquid found inside cells. cells.[2]  It is separated into compartments compartments by membranes. membranes. For example, example, the mitochondrial matrix separates matrix  separates the mitochondrion into mitochondrion into many compartments.

Membrane The cell membrane, membrane, or plasma membrane, is a biological a biological membrane that membrane that surrounds the cytoplasm of a cell. In animals, the plasma membrane is the outer boundary of the cell, while in plants and  prokaryotes it is usually covered by a cell wall. wall. This membrane serves to separate and protect a cell from its surrounding environment and is made mostly from a double layer of phospholipids, phospholipids, which are amphiphilic  amphiphilic  (partly hydrophobic and partly hydrophilic). hydrophilic). Hence, the layer is called a phospholipid a  phospholipid bilayer , or sometimes a fluid mosaic membrane. Embedded within this membrane is a variety of  protein molecules  protein molecules that act as channels and pumps that move different molecules into and out of the ce cell. ll.[3]

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FUNTIONS: The membrane FUNTIONS: membrane is semi-permeable semi-permeable,, and selectivel selectively y permeable, permeable, in that it can either  either  let a substance (molecule ( molecule or  or ion) ion) pass through freely, pass through to a limited extent or not pass through at all. Cell surface membranes also contain receptor  proteins   proteins that allow cells to detect external signaling molecules such as hormones. hormones. Cytoskeleton

The cytoskeleton acts to organize and maintain the cell's shape; anchors organelles in place; help helpss du duri ring ng endocytosis, endocytosis, the the upta uptake ke of ex exte tern rnal al mate materi rial alss by a ce cell ll,, an and d cytokinesis, cytokinesis, the separation of daughter cells after cell division; division; and moves parts of the cell in processes of growth and mobility. The eukaryotic cytoskeleton is composed of microfilaments, microfilaments, intermediate filaments and microtubules. microtubules. There are a great number of proteins associated with them, each controlling a cell's structure by directing, bundling, and aligning filaments.

Organelles Organelles are parts of the cell which are adapted and/or specialized for carrying out one or more vital functions, analogous to the organs of organs of the human body (such as the heart, lung, and kidney, with each organ performing performing a different different function). function).[3]  Both eukaryotic eukaryotic and prokaryotic prokaryotic cells have organelles, but prokaryotic organelles are generally simpler and are not membrane-bound. There are several types of organelles in a cell. Some (such as the nucleus and nucleus and golgi apparatus) apparatus) are are typi typica call lly y so soli lita tary ry,, whil whilee othe others rs (s (suc uch h as mitochondria, mitochondria, chloroplasts, chloroplasts,  peroxisomes   peroxisomes  and lysosomes)) can be numerous (hundreds to thousands). lysosomes Cell nucleus:.

In cell biology, biology, the nucleus (pl. nuclei ; from Latin  Latin  nucleus nucleus or  or nuculeus nuculeus,, meaning kernel  or seed   or  seed ) is a membrane-encl membrane-enclosed osed organelle  organelle  found in eukaryotic  eukaryotic  cells. cells. Eukaryotes usually have a single nucleus, nucleu s, but a few cell types, such as mammalian mammalian red blood cells, have no nuclei, nuclei, and a few others including osteoclasts have osteoclasts have many. many. Cell nuclei contain most of the cell's genetic material, material, organized as multiple multiple long linear linear DNA molecules in a complex with complex with a large variety of proteins of  proteins,, such as histones, histones, to form chromosomes. chromosomes. The genes within genes within these chromosomes are chromosomes are the cell's nuclear genome and genome and are structured in structured in such a way to promote cell function. The nucleus maintains the integrity of genes and controls the activities activ ities of the cell by regulating regulating gene expression —the nucleus is, therefore, the control center  of the cell. The main structures making up the nucleus are the nuclear envelope envelope,, a double membrane that encloses the entire organelle and isolates its contents from the cellular ce llular cytoplasm, cytoplasm, and the nuclear  matrix (which matrix  (which includes the nuclear lamina), lamina), a network within the nucleus that adds mechanical support, much like the cytoskeleton, cytoskeleton, which supports the cell as a whole. Functions

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Because the nuclear envelope is impermeable to large molecules, nuclear pores are pores are required to regul re gulat atee nuclear nuclear transport transport   of molecul molecules es across across the envelop envelope. e. The pores pores cross cross both nuclear  nuclear  membranes, providing a channel through channel through which larger molecules must be actively transported by carrier proteins while allowing free movement of small molecules and ions. ions. Movement of large molecules such as proteins and RNA through RNA through the pores is required for both gene expression and the maintenance of chromosomes. Although the interior of the nucleus does not contain any membrane-boun membr ane-bound d subcompartments subcompartments,, its contents are not unifo uniform, rm, and a number of  sub-nuclear  bodies   ex bodies exis ist, t, made made up of un uniq ique ue prot protei eins ns,, RNA RNA mole molecu cule les, s, an and d pa part rtic icula ularr parts parts of th thee ch chro romo moso some mes. s. Th Thee bestbest-kn know own n of thes thesee is the the nucleolus, nucleolus, which is mainly involved in the assemb ass embly ly of ribosomes. ribosomes. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA. mRNA.

Mitochondria

The mitochondrion  (plur (plural al mitochondria) is a double-membrane double- membrane-b -boun ound d organelle  organelle  found in most mo st eukaryotic  eukaryotic  organi organisms sms.. Some Some cells cells in some some multicellular   organisms may, however, lack  them (for example, mature mammalian red blood cells). cells). Mitochondria are commonly between 0.75 and 3 μm in μm in diameter [5] but vary considerably in size and structure. structure. Unless specifical specifically ly stained, stained, they are not visible.. These compartments or regions include inclu de the outer membrane, membrane, the intermembrane space, space, the inner membrane, membrane, and the cristae  cristae  and matrix.. matrix Although most of a cell's DNA is DNA is contained in the cell nucleus, nucleus, the mitochondrion has its own independent genome that genome that shows substantial similarity to bacterial to  bacterial  genomes. genomes. Functions: ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ………………………………………………………………………………………………………  PLASTID

The plastid is a membrane-bound  membrane-bound  organelle[1] found in the cells of cells of plants  plants,, algae, algae, and some other  eukaryotic organisms. eukaryotic  organisms. Plastids are the site of manufacture and storage of important chemical compounds used by the ce cell llss of autotrophic  autotrophic  eukaryotes. eukaryotes. They often contain contain  pigments   pigments  used used in  photosynthesis,  photosynthesis, and the types of pigments in a plastid determine the cell's color. They have a common evolutionary origin origi n and possess a double-stranded double-stranded DNA  DNA  molecu molecule le that is cir circul cular, ar, like that of  prokaryotic cells.. cells

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Plas Plasti tids ds that that co cont ntai ain n chlorophyll  chlorophyll  can can carr carry out out  photosynthesis   photosynthesis  an and d are call called ed chloroplasts. chloroplasts. Plastids can also store products like starch and starch and can synthesize fatty acids and acids and terpenes, terpenes, which can  be used for producing energy and as raw material for the synthesis of other molecules. For  exampl exa mple, e, the componen components ts of the  plant cuticle  cuticle  and its its epicuticular wax  wax  are synthesized by the epidermal cells  cells  from palmitic from  palmitic acid, acid, which which is synthesi synthesized zed in the chlorop chloroplas lasts ts of the mesophyll [2] tissue..  All plastids are derived from proplastids, which are present in the meristematic tissue meristematic regions  regions of the plant. Proplastids and young chloroplasts commonly divide by  binary fission, fission, but more mature chloroplasts also have this capacity.  Types

In plants In plants,, plastids may differentiate into differentiate into several forms, depending upon which function they play in the cell. cell. Undiffe Undifferen renti tiate ated d plast plastids ids ( proplastids) may de deve velo lop p in into to an any y of th thee fo foll llow owin ing g  proplastids) may [3] variants:   

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Chloroplasts: green plastids for photosynthesis Chloroplasts: for  photosynthesis;;  see also etioplasts , the predecessors of  chloroplasts Chromoplasts:: coloured plastids for pigment synthesis and storage Chromoplasts Gerontoplasts: control Gerontoplasts: control the disman dismantl tling ing of the photos photosynt ynthet hetic ic apparat apparatus us during during  plant senescence Leucoplasts: co Leucoplasts: colo lour urle less ss plas plasti tids ds for for monoterpene  monoterpene  synthesis; synthesis; leucoplast leucoplastss sometimes sometimes differentiate into more specialized plastids: o

Amyloplasts:: for starch storage Amyloplasts starch storage and detecting gravity (for gravity (for geotropism) geotropism)

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Elaioplasts:: for storing fat Elaioplasts

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Proteinoplasts:: for storing and modifying protein Proteinoplasts modifying protein

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Tannosomes:: for synthesizing and producing tannins and Tannosomes tannins and polyphenols

Endoplasmic reticulum

The endoplasmic reticulum (ER ) is a type of organelle found organelle found in eukaryotic cells that cells that forms an interconnected network of flattened, membrane-enclosed sacs or tube-like structures known as cisternae.. The cisternae The memb membra rane ness of the the ER ar aree co cont ntin inuo uous us wi with th th thee ou oute terr nuclear membrane. membrane. The endoplasmic endopl asmic reticulum reticulum occurs in most types of eukaryotic eukaryotic cells, cells, but is absent from red blood cells and cells  and spermatozoa. spermatozoa. There are two types of endoplasmic reticulum: rough (granular) and smooth (agranular). The outer (cytosolic (cytosolic)) face of the rough endoplasmic reticulum is studded with ribosomes that ribosomes that are the sites of protein of protein synthesis. synthesis. The rough endoplasmic reticulum is especially prominent in cells such

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as hepatocytes. hepatocytes. The smooth smooth endopl endoplasm asmic ic reticu reticulum lum lacks ribosome ribosomess and function functionss in lipid manufa man ufactu cture re and metabo metabolis lism, m, the produc productio tion n of steroid hormones, hormones, and and detoxification. detoxification.[1]  The smooth ER is especially abundant in mammalian liver  and  and gonad cells. gonad cells. The general structure of the endoplasmic reticulum is a network of membranes called cisternae. cisternae. These The se sac-li sac-like ke struct structure uress are held togeth together er by the cytoskeleton. cytoskeleton. The The  phospholipid membrane enclos enc loses es the cisterna cisternall space space (or lumen), lumen), which which is contin continuous uous with the  perinuclear space  space  but separate from the cytosol. cytosol. Functions

 The functions of the endoplasmic reticulum can be summarized as the synthesis and export of   proteins and membrane lipids, but varies between ER and cell type and cell function. The quantity of both rough and smooth endoplasmic reticulum in a cell can slowly interchange from one type to the other, depending on the changing metabolic activities of the cell. Transformation can include embedding of new proteins in membrane as well as structural changes. Changes in  protein content may occur without noticeable structural changes. Golgi apparatus:

The Golgi apparatus, also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle   found organelle found in in most most eukaryotic  eukaryotic  cells. cells.[1] It was identified in 1897 by the Italian scientist Camillo Golgi and Golgi and named after him in 1898.[2]  Part of the endomembrane system in system in the cytoplasm, cytoplasm, the Golgi apparatus packages apparatus  packages proteins into proteins into membrane-bound   vesicles inside membrane-bound vesicles inside the cell before the vesicles are sent to their destination. The Golgi apparatus resides at the intersection of the secretory, lysosomal, and endocytic pathways. It is of particular importance in processing proteins processing proteins for  for secretion, secretion, containing containing a set of glycosylation enzymes   that attach various sugar monomers to proteins as the proteins move through the enzymes apparatus. Function

The Golgi apparatus is a major collection and dispatch station of protein products received from the endoplasmic reticulum  reticulum  (ER). (ER). Proteins Proteins synthes synthesize ized d in the ER are package packaged d int into o vesicles, vesicles, which then fuse with the Golgi apparatus. These cargo proteins are modified and destined for  secretion via exocytosis or exocytosis or for use in the cell. In this respect, the Golgi can be thought of as similar to a post office: it packages and labels items which it then sends to different parts of the ce cell ll or to the extracellular space. space. The Golgi Golgi appara apparatus tus is also involved involved in lipid  lipid  transport and [10] lysosome formation. lysosome  formation.  

Lysosomes   cont contai ain n digestive digestive enzymes enzymes  (aci (acid d hydrolases). hydrolases). They digest excess or  Lysosom Lysos omes es Lysosomes worn-out organelles, organelles, food particles, and engulfed viruses or viruses or bacteria  bacteria..

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Peroxisomes have enzymes that rid the cell of toxic peroxides Peroxisomes have toxic  peroxides.. The cell could not house these destructive enzymes if they were not contained in a membrane-bound system. [3] Centrosome: the cytoskeleton organiser: The centrosome produces centrosome produces the microtubules of microtubules of a cell – a ke key y comp compon onent ent of the cytoskeleton. cytoskeleton. It dire direct ctss the the tr tran ansp spor ortt th thro roug ugh h th thee ER   and the the Golgi apparatus.. Centrosomes are composed of two centrioles, apparatus centrioles, which separate during cell division and division and help in the formation of the mitotic spindle. spindle. A single centrosome is present in the animal cells. cells. They are also found in some fungi and algae cells. Vacuoles:

A vacuole  is a membrane-bound membrane-bound organelle which organelle which is present in all plant all  plant   and fungal  fungal  cells  cells  and [1] [2][ [2][verif verificatio ication n needed  needed ] some  protist,  protist, animal   an and  bacterial   bacterial  cells   an and d ar aree es esse sent ntia iall lly y enclo enclose sed d compartments which are filled with water containing inorganic and organic molecules including enzymes in enzymes  in solution, solution, though in certain cases they may contain solids which have been engulfed. Vacuoles are formed by the fusion of multiple membrane vesicles and vesicles and are effectively just larger  [3] forms of these.  The organelle has no basic shape or size; its structure varies according to the requiThe function and significance of vacuoles varies greatly according to the type of cell in which they are present, having much greater prominence in the cells of plants, fungi and certain  protists than those of animals and bacteria. In general, the functions of the vacuole include: 

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Isolating materials that might be harmful or a threat to the cell Containing waste products Containing water in plant cells Maintaining internal hydrostatic pressure or pressure or turgor  within  within the cell Maintaining an acidic internal acidic internal pH  pH Containing small molecules Exporting unwanted substances from the cell Allows plants to support structures such as leaves and flowers due to the pressure of the central vacuole By increasing in size, allows the germinating plant or its organs (such as leaves) to grow very quickly and using up u p mostly just water.[4] In seeds, stored proteins needed for germination are kept in 'protein bodies', which are modified vacuoles.

The ribosome  ribosome  is a large large compl complex ex of RNA  RNA  an and  protein   protein  molecules.[3]  They each Ribosomes: The consist of two subunits, and act as an assembly line where RNA from the nucleus is used to synthesise proteins from amino acids. Ribosomes can be found either floating freely or bound to a membra membrane ne (the (the rough rough endopl endoplasm asmati aticc reticu reticulum lum in eukaryo eukaryotes tes,, or the cell cell membra membrane ne in [18]

 prokaryotes).

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Structures outside the cell membrane

Many cells also have structures which exist wholly or partially outside the cell membrane. These structures are notable because they are not protected from the external environment by the semipermeable cell membrane. membrane. In order to assemble these structures, their components must be carried across the cell membrane by export processes. Plant cell walls

Plant cell walls vary from 0.1 to several µm in thickness. Up to three strata or layers may be found in plant cell walls: 

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The primary cell wall, generally a thin, flexible and extensible layer formed while the cell is growing. The secondary cell wall, a thick layer formed inside the primary cell wall after the cell is fully grown. It is not found in all cell types. Some cells, such as the conducting cells in xylem,, possess a secondary wall containing lignin, xylem lignin, which strengthens and waterproofs the wall. The middle lamella, a la laye yerr rich rich in  pectins.  pectins. This outermost layer forms the interface  between adjacent plant cells and glues them together 

Composition In the primary (growing) (growing) plant cell wall, the major carbohydrates  carbohydrates  are cellulose, cellulose, hemicellulose and pectin and  pectin.. The outer part of the primary cell wall of the plant epidermis is usually impregnated with cutin and cutin and wax, wax, forming a permeability barrier known as the plant the  plant cuticle cuticle.. Secondary cell walls contain a wide range of additional compounds that modify their mechanical  properties and permeability. The major  polymers   polymers  that mak makee up wood (largely wood (largely secondary cell walls) include:  

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cellulose, 35-50% xylan,, 20-35%, a type of hemicellulose xylan lignin, 10-25%, a complex phenolic polymer that penetrates the spaces in the cell wall lignin,  between cellulose, hemicellulose and pectin components, driving out water and strengthening the wall.

Secondary walls - especially in grasses g rasses - may also contain microscopic silica crystals, silica crystals, which may strengthen the wall and protect it from herbivores. Cells with secondary cell walls can be rigid, as in the g gritty ritty sclereid cells sclereid cells in pear  in pear  and  and quince fruit. quince fruit. Celll to cell Cel cell commun communicat ication ion is possib possible le through through  pits   pits  in the second secondary ary cell wall that that all allow ow  plasmodesmata to connect cells through the secondary cell walls.

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The middle middle lamella  lamella  is laid down first, first, formed formed from from the cell plate  plate  during during cytokinesis, cytokinesis, and the [clarification needed ]  primary cell wall is then deposited inside the middle lamella.   The cells are held toget to gethe herr and and sh shar aree the the ge gela lati tinou nouss memb membra rane ne ca call lled ed th thee middl middlee lamella lamella,, wh whic ich h co cont ntai ains ns magnesium   and magnesium and calcium  calcium  pectates   pectates  (s (sal alts ts of  pectic acid). acid). Cells Cells interact interact though though  plasmodesmata,  plasmodesmata, which are inter-connecting channels of cytoplasm that connect to the protoplasts of adjacent cells across the cell wall. Functions:

Cell walls serve similar purposes in those organisms that possess them. They may give cells rigidity and strength, offering protection against mechanical stress. In multicellular organisms, they permit the organism to build and hold a definite shape (morphogenesis ( morphogenesis). ). Cell walls also limit the entry of large molecules that may be toxic to the cell. They further permit the creation of stable osmotic environments osmotic environments by preventing osmotic lysis and lysis and helping to retain water. Their  compos com posit ition ion,, proper propertie ties, s, and form form may change change during during the cell cycle  cycle  and depend on growth conditions.

In most cells, the celltensile wall isstrengt flexible, meaning that it will bend rather than holding a fixed shape,  but has considerable

Cytoplasm inclusions (non -living)/ ergastic materials

  They are diverse intracell intracellular ular [1]  non-living non-living substances substances [2]  that are not able to carry out any metabolic activity and are not bound by membranes. Inclusions are stored nutrients, secretory  products, and pigment granules. 1. 1.A A carbohydrate  i s a  biomolecule   biomolecule  consistin consisting g of carbon  carbon  (C), (C), hydrogen  hydrogen  (H) and and oxygen  oxygen  (O) atoms, ato ms, usuall usually y with with a hydrog hydrogen–o en–oxyge xygen n atom  atom  ratio of 2:1 (as in water) and thus with the empirical formula C formula Cm(H2O)n (where m may be different from n) The major dietary carbohydrates Class

Sugars   Sugars

Subgroup

Components

Monosaccharides

Glucose, Glucose, galactose, galactose, fructose, fructose, xylose  xylose 

Disaccharides

Sucrose, Sucrose, lactose, lactose, maltose, maltose, trehalose  trehalose 

Polyols

Sorbitol, Sorbitol, mannitol  mannitol 

Oligosaccharides  Malto-oligosaccharides Oligosaccharides 

Other oligosaccharides

Maltodextrins  Maltodextrins  Raffinose, Raffinose, stachyose, stachyose, fructo-oligosaccharides

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Starch Polysaccharides   Non-starch Polysaccharides

 polysaccharides

Amylose, Amylose, amylopectin, amylopectin, modified starches Glycogen, Cellulose, Glycogen, Cellulose, Hemicellulose, Hemicellulose, Pectins, Pectins, Hydrocolloid

2. Proteins are large biomolecules large biomolecules,, or macromolecules, macromolecules, consisting of one or more long chains of  amino acid  acid  residues. residues. Protei Proteins ns perfor perform m a vast vast array array of functi functions ons within within organisms, organisms, including catalysing metabolic reactions, reactions, DNA replication, replication, responding to stimuli, stimuli, providin providing g structure to cells   and organisms, cells organisms, and transporting molecules from molecules from one location to another. Proteins differ  from one another primarily in their sequence of amino acids, which is dictated by the nucleotide sequence   of thei sequence theirr genes, genes, and which which us usua uall lly y re resu sult ltss in  protein folding  folding  in into to a specif specific ic threedimensional structure that structure that determines its activity.

3. In In  biology and  biology and biochemistry  biochemistry,, a lipid is a biomolecule a  biomolecule that  that is soluble in nonpolar  solvents.   solvents.[3]  Non-polar solvents  solvents  ar aree typic typical ally ly hydrocarbons  hydrocarbons  used used to dissol dissolve ve other other natura naturally lly occurri occurring ng hydrocarbon hydroc arbon lipid lipid molecules  molecules  that that do not (or do not easily easily)) dissol dissolve ve in water, water, includi including ng fatty acids,, waxes, acids waxes, sterols, sterols, fat-soluble vitamins (such vitamins (such as vitamins A, D, E, and K), monoglycerides, monoglycerides, diglycerides,, triglycerides, diglycerides triglycerides, and phospholipids and phospholipids.. Other cell products

astringent,  polyphenolic   polyphenolic  biomolecules that  biomolecules that bind to and 1.tannins   (or tannoids) are a class of astringent,  precipitate   proteins and  precipitate proteins and various other organic compounds including amino acids acids and  and alkaloids. alkaloids. The tannin compounds are widely distributed in many species of plants, where they play a role in  protection from  predation,  predation, and perhap perhapss al also so as  pesticides,  pesticides, and might help in regulating plant [1] growth.   The astringency from astringency from the tannins is what causes the dry and puckery feeling in the mouth following the consumption of unripened fruit, red wine or tea. [2] Likewise, the destruction or modification of tannins with time plays an important role when determining harvesting times. 2. An essential oil is a concentrated hydrophobic liquid hydrophobic liquid containing volatile (easily volatile (easily evaporated at normal temperatures) aroma compounds from plants from  plants.. Essential oils are also known as volatile oils, ethereal oils, aetherolea, or simply as the oil of the plant from which they were extracted, such suc h as oil of clove. clove. An essential oil is oil is "essential "essential"" in the sense that it contains contains the "essence "essence of" the plant's fragrance—the characteristic fragrance of the plant from which it is derived. d erived. 3.In  polymer chemistry  3.In polymer chemistry  and materials science, science, resin  is a soli solid d or highly highly viscous substance viscous substance of  [1]  plant or synthetic origin that is typically convertible into polymers into  polymers..  Resins are usually mixtures of organic compounds compounds.. This article focuses on naturally-occurring resins.

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Plants secrete resins for their protective benefits in response to injury. The resin protects the  plant from insects and pathogens.[2] Resins confound a wide range of herbivores, insects, and  pathogens, while the volatile phenolic volatile  phenolic compounds may compounds  may attract benefactors such as parasitoids as parasitoids or   or  [3]  predators of the herbivores that attack the plant.    are polysaccharides  polysaccharides of  of natural origin, capable of causing a large increase in a 4. Natural gums are solution’s viscosity, viscosity, even at small concentrations concentrations.. They are mostly botanical mostly  botanical gums g ums,, found in the woody elements of plants or in seed coatings. class of naturally occurring  occurring  organic compounds  compounds  that that mostly mostly contain contain  basic 5. Alkaloids  are a class nitrogen   atoms. This group also includes some related compounds with neutral [2]  and even nitrogen weakly acidic properties. acidic properties.[3] Some synthetic compounds of similar structure may also be termed alkaloids.[4] In addition to carbon, carbon, hydrogen  hydrogen  and nitrogen, nitrogen, alkaloids alkaloids may also contain oxygen, oxygen, [5] sulfur  and,  and, more rarely, other elements such as chlorine, chlorine, bromine,  bromine, and phosphorus and phosphorus..   Alkaloids are produced by a large varie Alkaloids variety ty of organisms organisms including including  bacteria,  bacteria, fungi, fungi,  plants,  plants, and animals 6. The The organic acids occupy a central position in the metabolism of plants. They are early  products of They photosynthesis andproducts as suchofserve as precursors   formore the reduced synthesis of many other  compounds. also arise as the degradation of the chemical entities in the plant. 7. Crystals of various minerals are found in plants as waste products. These crystals are made up of calcium oxalate  or calcium carbonate. The The cr crys ysta tals ls of calcium carbonate  are found in cellulose cellulo se walls. In banyan (Ficus) (Ficus) leaves are developed in the shape of bunch of grapes and are said as Cystolith.  

Topic: Plant tissues

Plant tissues can also be divided differently into two types: 1. Meri Merist stem emat atic ic tiss tissues ues 2. Perm Perman anen entt tiss tissue ues. s.

Meristematic tissues Meristematic tissue  tissue  consists of actively dividing cells, and leads to increase in length and thickness of the plant. The primary growth of a plant occurs only in certain, specific regions, such as in the tips of stems or roots. It is in these regions that meristematic tissue is present. Cells in these tissues are roughly spherical or polyhedral, to rectangular in shape, and have thin cell walls. New cells produced by meristem are initially those of meristem itself, but as the new cells grow gro w and mature mature,, their their charac character teris istic ticss slowly slowly change change and they they become become differ different entiat iated ed as components of the region of occurrence of meristematic tissues, they are classified as:

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Apical Meristem - It is present at the growing tips of stems and roots and increases the length of the stem and root. They form growing parts at the apices of roots and stems and are responsible for the increase in length, also called primary growth. This meristem is responsible for the linear growth of an organ. Lateral Meristem - This meristem consists of cells which mainly divide in one plane and cause the organ to increase in diameter and growth. Lateral meristem usually occurs  beneath the bark of the tree in the form of Cork Cambium and in vascular bundles of  dico dicots ts in the form of vascular cambium. cambium. The activity of this cambium results in the formation of secondary growth. Intercalary Meristem  - This meristem is located in between permanent tissues. It is usually present at the base of the node, internode and on leaf base. They are responsible for growth in length of the plant and increasing the size of the internode, They result in  branch formation and growth.

The cells of meristematic tissues are similar in structure and have thin and elastic primary cell wall made up of cellulose. cellulose. They are compactly arranged without inter-cellular spaces between them. the m. Each cell contains contains a dense dense cytoplasm  cytoplasm  an and d a pr prom omin inen entt nucleus. nucleus. Dens Densee  protoplasm   protoplasm  of  merist mer istema ematic tic cells cells contain containss very very few vacuole vacuoles. s. Normal Normally ly the merist meristemat ematic ic cells cells are oval, oval,  polygonal or  polygonal  or rectangular in shape. Merist Meri stem emat atic ic tiss tissue ue ce cell llss have have a la larg rgee nu nucl cleus eus wi with th smal smalll or no va vacuo cuole les, s, th they ey ha have ve no intercellular spaces.

Permanent tissues Permanent tissues may be defined as a group of living or dead cells formed by meristematic tissue and have lost their ability to divide and have permanently placed at fixed positions in the  plant body. Meristematic tissues that take up a specific role lose the ability to divide. This  process of taking up a permanent shape, size and a function is called cellular differentiation. differentiation. Cells of meristematic tissue differentiate to form different types of permanent tissues. There are 3 types of permanent tissues: 1. simp simple le per perma manen nentt tiss tissues ues 2. co comp mple lex x perma permane nent nt tiss tissue uess 3. specia speciall or secreto secretory ry tissue tissuess (glandu (glandular lar). ).

 Simple tissues A group of cells which are similar in origin; similar in structure and similar in function are called simple permanent tissue. They are of four types: 1. Parenchyma 2. Collenchyma 3. Sclerenchyma

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4. Epidermis (botany) Parenchyma

Parenchyma ( para  para - 'beside'; enchyma enchyma  - 'tissue') is the bulk of a substance. In plants, it consists of  relatively unspecialized living cells with thin cell walls that are usually loosely packed so that intercellular spaces are found between cells of this tissue. These are generally isodiametric, in sh shap ape. e. This This tiss tissue ue provi provides des su supp ppor ortt to plant plantss and al also so st stor ores es fo food od.. In so some me si situ tuat atio ions ns,,  parenchyma contains chlorophyll and performs photosynthesis, in which case it is called a chlorenchym chlor enchyma. a. In aquatic plants, large air cavities cavities are present present in parenchyma parenchyma to give support to them to float on water. Such a parenchyma type is called aerenchyma. Some of the parenchyma cells have metabolic waste and is known as idioblast. Spindle shape fiber also contained into this cell to support them and known as prosenchyma, succulent parenchyma also noted. Collenchyma

 

Cross-section of a flax plant flax plant stem with several layers of different tissue types: 1. Pith 2. Protoxylem 3. Xylem I Xylem I 4. Phloem I Phloem I 5. Sclerenchyma ( Sclerenchyma ( bast  bast fibre) fibre) 6. Cortex 7. Epidermis

Cross section of collenchyma cells Collenchyma is Greek word where "Collen" means gum and "chyma" means infusion. It is a Collenchyma is living tissue of primary body like Parenchyma. Parenchyma. Cells are thin-walled but possess thickening of  cellulose,, water and pectin cellulose and  pectin   substances ( pectocellulose)  pectocellulose) at the corners where a number of cells

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 join together. This tissue gives tensile strength to the plant and the cells are compactly arranged and have very little inter-cellular spaces. It occurs chiefly in hypodermis of hypodermis of stems and leaves. It is absen absentt in monocots  monocots  and in roots. Sometimes it contains chlorophyll which can help them  photosynthesize. Collenchy Collen chymat matous ous tissue tissue acts acts as a suppor supportin ting g tissu tissuee in stems stems of young young plants plants.. It provid provides es mechanical mechan ical support, elasticity, elasticity, and tensile tensile strength to the plant body. It helps in manufacturing manufacturing sugar and storing it as starch. It is present in the margin of leaves and resists tearing effect of the wind. Schlerenchyma

Schlerenchyma is Greek word where "Schlerena" means hard and "chyma" means infusion. This Schlerenchyma is tissue consists of thick-walled, dead cells and protoplasm is negligible. n egligible. These cells have hard and extremely thick secondary walls due to uniform distribution and high secretion of lignin. lignin. They do not have intermolecular space between them. Lignin deposition is so thick that the cell walls  become strong, rigid and impermeable to water which is also known as a stone cell or sclereids. These tissues are mainly of two types: sclerenchyma fiber and sclereids. Schlerenchyma cells have a narrow lumen and are long, narrow and unicellular. .

Complex permanent tissue The complex tissue consists of more than one type of cells which work together as a unit. Complex tissues help in the transportation of organic material, water, and minerals up and down the plants. That is why it is also known as conducting and vascular tissue. The common types of  complex permanent tissue are:  

Xylem or wood Phloem or bast.

Xylem and phloem together form vascular bundles.  Xylem

Xylem consists of:

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Tracheids Vessel members

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Xylem fibres

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Xylem parenchyma

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Cross section of 2-year-old Tilia Americana, highlighting xylem ray shape and orientation. Xylem serves Xylem  serves as a chief conducting tissue of vascular plants. plants. It is responsible for the conduction of water and mineral ions/salt. Xylem tissue is organized in a tube-like fashion along the main axes of stems and roots. It consists of a combination of   parenchyma cells, fibers, vessels, tracheids, and ray cells. Longer tubes made up of individual cells are vessels tracheids, while vessel members are open at each end. Internally, there may be  bars of wall material extending across a cross the open space. These cells are joined end to end to form long tubes. Vessel members and tracheids are dead at maturity. Tracheids have thick secondary cell walls and are tapered at the ends. They do not have end openings such as the vessels. The tracheids end overlap with each other, with pairs of pits present. The pit pairs allow water to pass from cell to cell. Though most conduction in xylem tissue is vertical, lateral conduction along the diameter of a stem is facilitated via rays.[1] Rays are horizontal rows of long-living parenchyma cells that arise out of the vascular cambium. In trees and other woody plants, rays radiate out from the center of  stems and roots and appear like spokes on a wheel in cross section. Rays, unlike vessel members and tracheids, are alive at functional maturity. [2]  Phloem

Phloem consists of:

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Sieve tube Companion cell

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Phloem fibre

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Phloem parenchyma.

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Phloem is an equally important plant tissue as it also is part of the 'plumbing system' of a plant. Primar Pri marily ily,, phloem phloem carrie carriess dissol dissolved ved food food substa substance ncess through throughout out the plant. plant. This This conduct conduction ion system is composed of sieve-tube member and companion cells that are without secondary walls. The parent cells of the vascular cambium produce both xylem and phloem. This usually also includes fibers, parenchyma and ray cells. Sieve tubes are formed from sieve-tube members laid end to end. The end walls, unlike vessel members in xylem, do not have openings. The end

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walls, however, are full of small pores where cytoplasm extends from cell to cell. These porous connections are called sieve plates. In spite of the fact that their cytoplasm is actively involved in the conduction of food materials, sieve-tube members do not have nuclei at maturity. It is the companion cells that are nestled between sieve-tube members that function in some manner   bringing about the conduction of food. Sieve-tube members that are alive contain a polymer  called callose, a carbohydrate polymer, forming the callus pad/callus, the colourless substance that covers the sieve plate. Callose stays in solution as long as the cell contents are under   pressure. Phloem transports food and materials in plants plants upwards and downwards as required.

Plant secretory tissue The tissues that tissues that are concerned concerned with the secretion secretion of gums, gums, resins, resins, volatile oils, nectar   latex, latex, and other substances in plants are called secretory tissues These tissues are divided into two groups1. La Lati tici cife fero rous us tiss tissues ues 2. Glan Glandu dula larr tis tissu sues es Laticiferous tissues

These consist of thin walled, greatly elongated and much branched ducts containing a milky or  yellowish colored juice known as latex. latex. They contain numerous nuclei which lie embedded in the thin lining layer of protoplasm of  protoplasm.. They irregularly distributed in the mass of parenchymatous cells. Laticiferous ducts, in which latex are found are again two types1. Latex Latex cell cell or non-ar non-artic ticula ulate te latex latex ducts ducts 2. Latex Latex vesse vessels ls or art articu iculat latee latex latex

Latex cells Also called as "non-articulate latex ducts", these ducts are independent units which extend as  branched structures for long distances in the plant body. They originate as minute structures, elongate quickly and by repeated branching ramify in all directions but do not fuse together. Thus a network is not formed as in latex vessels.

Latex vessel Also called "articulate latex ducts", these ducts or vecssels are the result of anastamosing of  many cells together. They grow more or less as parallel ducts which by means of branching and frequent anastamose form a complex network. Latex vessels are commonly found in many angiosperm families Papaveraceae, Papaveraceae, Compositae, Compositae, Euphorbiaceae, Euphorbiaceae, Moraceae, Moraceae, etc.

Function The function of laticiferous ducts is not clearly understood. They may also act as food storage organs or as reservoir of waste products. They may also act as translocatory tissues.

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Glandular tissues

This tissue consists of special structures; the glands. These glands contain some secretory or  excretory products. A gland may consist of isolated cells or small group cells with or without a central cavity. They are of various kinds and may be internal or external. Internal glands are  

Oil-gland secreting essential oils, as in the fruits and leaves of orange, lemon.

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Mucilage secreting glands, as in the betel be tel leaf 

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Glands secreting gum, resin, tannin, etc.

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Digestive glands secreting enzymes or digestive agents

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Special water secreting glands at the tip of veins

External glands are commonly short hairs tipped by glands. They are

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water-secreting hairs or glands, Glandular hairs secreting gum like substances as in tobacco tobacco,, plumbago,  plumbago, etc.

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Glandular hairs secreting irritating, poisonous substances, as in nettles

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Honey glands, as in carnivorous plants plants..

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In  plant anatomy, anatomy, tissues are categorized categorized broadly into three tissue tissue systems: systems: the epidermis, epidermis, the ground tissue, tissue, and the vascular tissue. tissue. 1. Epidermal cell: Cells forming the outer surface of the leaves and leaves and of the young plant

forming g the outer outer surface surface of the leaves and leaves and of the young plant body. The Epidermis  - Cells formin epidermis is a single layer of cells that covers the leaves, leaves, flowers, flowers, roots and roots and stems of stems of plants  plants.. It forms a boundary between the plant and the external environment. The epidermis serves severa sev erall functi functions ons:: it protec protects ts agains againstt water water loss, loss, regula regulates tes gas exchange, exchange, secretes secretes metabolic metabolic compounds, and (especially in roots) absorbs water and mineral nutrients. The epidermis of most leave le avess sh show owss dorsoventra dorsoventrall anatomy anatomy: the upper upper (adaxi (adaxial) al) and lower lower (abaxi (abaxial) al) surfac surfaces es have somewhat different construction and may serve different functions. Woody stems and some other  stem structures produce a secondary covering called the periderm the  periderm that  that replaces the epidermis as the protective covering. stomata (sing., stoma), part Guard cell: The leaf and stem epidermis is covered with pores called stomata (sing., of a stoma complex  consisting of a pore surrounded on each side by chloroplast-containing guard cells, and subsidiary ry cells  that lack chloroplasts. The stomata complex and tw two o to four four subsidia

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regulates the exchange of gases and water vapor between the outside air and the interior of the leaf. 2. Vascular tissue  - The primary primary componen components ts of vascul vascular ar tissue tissue are the xylem  xylem  and and  phloem.  phloem. These transport fluids and nutrients internally. Ground nd tis tissu suee is les esss differentiated  differentiated  than than other other ti tissu ssues. es. Ground Ground ti tissu ssuee Ground tissue Ground tissue  - Grou manufactur manuf actures es nutrients nutrients by  photosynthesis   photosynthesis  and stores stores reserv reservee nutrie nutrients nts.. The ground tissue  of   plants includes all tissues that are neither dermal nor dermal nor vascular . It can be divided into three types  based on the nature of the cell walls. 1. Parenchyma cells have thin primary thin  primary walls and walls and usually remain alive after they become mature. Parenchyma forms the "filler" tissue in the soft parts of plants, and is usually  present in cortex, cortex, pericycle,  pericycle, pith,  pith, and medullary rays in rays in primary stem and stem and root. root. 2. Collenchyma cells have thin primary walls with some areas of secondary thickening. Collenchyma provides extra mechanical and structural support, particularly in regions of  new growth. 3. Sclerenchyma  cells have have thick thick lignified  lignified  secondary walls and walls and often die when mature. Sclerenchyma provides the main structural support to a plant.[ Cortex is the outermost layer of a stem or root in a plant. The cortex is the outermost layer of the stem   or root  stem root  of a plan plant, t, bounded bounded on the the ou outs tsid idee by the epidermis and epidermis and on the inside by the endodermis.. In plants, endodermis plants, it is compos composed ed mostly mostly of differentiated cells, cells, usually large thin-walled  parenchyma cells  parenchyma  cells of the ground tissue system. tissue system. The outer cortical cells often acquire irregularly thickened cell walls, and are called collenchyma cells. Some of the outer cortical cells may contain chloroplasts. chloroplasts. It is responsible for the transportation of materials into the central cylinder  of the root through diffusion and may also be used for food storage in the form of starch.[1] 

The endodermis  is the central, central, innermo innermost st layer of cortex cortex in some some land plants. plants. It is made of  compact living cells surrounded by an outer ring of endodermal cells that are impregnated with hydrophobic substances hydrophobic  substances (Casparian (Casparian Strip) Strip) to restrict apoplastic flow apoplastic flow of water to the inside. [1] The endodermis is the boundary between the cortex and the stele. stele. The pericycle  is a cyl cylinder nder of  parenchyma   parenchyma  or sclerenchyma sclerenchyma   cells cells that that li lies es just just inside inside the endodermis and endodermis  and is the outer most part of the stele of stele of plants. Although it is composed of non-vascular parenchyma cells, it's still considered part of the vascular cylinder because it arises from the pro-cambium as do the vascular tissues it surrounds.

Unit 6

Topic: Physiological Functions of Plant

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Diffusion is the net movement of molecules from a region of higher concentration to a region of  lower concentration. Diffusion is driven by a gradient in chemical potential of the diffusing species.

Biologists often use the terms "net movement" or "net diffusion" to describe the movement of  Biologists often ions or molecules by diffusion. For example, oxygen can diffuse through cell membranes so long as there is a higher concentration of oxygen outside the cell. However, because the movement of  mole mo lecu cule less is rand random om,, oc occas casio iona nall lly y oxyge oxygen n mole molecul cules es move move ou outt of th thee ce cell ll (a (aga gain inst st th thee co conc ncent entra rati tion on gradi gradien ent) t).. Beca Becaus usee ther theree ar aree more more ox oxyge ygen n mole molecu cule less outsi outside de th thee ce cell ll,, th thee  probability that  probability  that oxygen molecules will enter the cell is higher than the probability that oxygen molecules will leave the cell. Therefore, the "net" movement of oxygen molecules (the difference  between the number of molecules either entering or leaving the cell) is into the cell. In other  words, there is a net movement  of  of oxygen molecules down the concentration gradient. Imbibition is a special type of diffusion when water is absorbed by solids- colloids causing colloids causing an enormous increase in volume. Examples include the absorption of water by seeds [1]  and dry wood. If it were not for the pressure due to imbibition, seedlings would not have been able to emerge out of soil into the open; they probably would not have been able to establish.

Imbibition is also diffusion since water surface potential movement is along a concentration gradient; the seeds and other such materials have almost no water hence they absorb water easily. Water potential gradient between the absorbent and the liquid imbibed is essential for imbibition. In addition, for any substance to imbibe any liquid, affinity between the adsorbant and the liquid is also a prerequisite. Imbibition occurs when a wetting fluid displaces a non-wetting fluid, contrary to drainage where a non-wetting phase displaces the wetting fluid. The two processes are governed by different mechanisms. One example example of imbibi imbibitio tion n that that is found in nature nature is the absorption  absorption  of water water by hydrophilic colloids.. Matrix potential contributes colloids potential contributes significantly to water in such substances. Examples of plant material which exhibit imbibition are dry seeds before germination. Imbibition can also entrain the genetic clock that controls circadian rhythms in Arabidopsis thaliana and (probably) other   plants. Another example is that of imbibition in the Amott test. test. solvent molecules through a selectively permeable Osmosis is the spontaneous net movement of solvent molecules membrane into membrane  into a region of higher solute solute concentration,  concentration, in the direction that tends to equalize the [2][3] [4] [2][3][4]  It may also be used to describe a physical process in solute concentrations on the two sides. which any solvent moves across a selectively permeable membrane (permeable to the solvent, [5][6] [6]  Osmosis can be made  but not the solute) separating two solutions of different concentrations. [5] [7] to do work.  Osmotic pressure is pressure is defined as the external pressure external pressure required  required to be applied so that there is no net movement of solvent across the membrane. Osmotic pressure is a colligative property, property, meaning that the osmotic pressure depends on the molar concentration of concentration of the solute but not on its identity.

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Osmosis is a vital process in biological in  biological systems, systems, as biological as biological membranes are membranes are semipermeable. In general, these membranes are impermeable to large and polar  and  polar  molecules,  molecules, such as ions, ions,  proteins,  proteins, and polysaccharides and  polysaccharides,, while being permeable to non-polar or hydrophobic molecules hydrophobic molecules like lipids as lipids as well as to small molecules like oxygen, carbon dioxide, nitrogen, and nitric oxide. Permeability depends on solubility, charge, or chemistry, as well as solute size. Water molecules travel through the plasma membrane, tonoplast membrane (vacuole) or protoplast by diffusing across the the ph phos osph phol olip ipid id bila bilaye yerr via via aquaporins  aquaporins  (small (small transm transmemb embran ranee protei proteins ns simil similar ar to those those responsible for facilitated diffusion diffusion   and ion channels). channels). Osmosis Osmosis provides the primary primary means by whiich water   is trans wh transpo port rted ed into into and out of cells. cells. Th The turgor   pressu pressure re of a cell cell is largely largely maintained by osmosis across the cell membrane between the cell interior and its relatively hypotonic environment. Importance of osmosis in plant life: 

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Root hair absorbs water from the soil by the process of osmosis; at least entry of water is controlled by osmosis. From the root hairs, cell to cell osmosis takes place until the cortical cell if the root  becomes saturated with water. The osmotic pressure generated in the root cortex is responsible for the forcing water into the xylem vessels, and possibly upwards through them at least to some height. Osmosis makes cell turgid. This turgidity gives a certain amount of turgidity to the young, soft parts of the plant body.

TURGIDITY:

the  plasma membrane against membrane against the cell Turgor pressure is the force within the cell that pushes the plasma [1] wall..   It is also wall also call called ed hydros hydrostatic tatic pressure pressure,, and more more int intric ricate ately ly define defined d as the press pressure ure [2] measured measu red by a fluid, fluid, measured measured at a certain certain point within within itself when at equilibrium. equilibrium.  Generally, turgorr pressure is caused by the osmotic flow turgo osmotic flow of water and occurs in plants in  plants,, fungi, fungi, and bacteria and  bacteria.. [3] The phenomenon is also observed in protists in  protists that  that have cell walls.  This system is not seen in animall cells, seeing how the absenc anima absencee of a cell wall would cause the cell to lyse when under too [4] much pressure.  The pressure exerted by the osmotic flow of water is called turgidity. It is caused by the osmotic flow of water through a selectively permeable membrane membrane.. Osmotic flow of water through a semipermeable membrane is when the water travels from an area with a lowsolutee concentrati solut concentration, on, to one with a higher-solu higher-solute te concentrati concentration. on. In plants, plants, this entails entails the water  moving from the low concentration solute outside the cell, into the cell's vacuole. vacuole.[5]  Mechanism

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Osmosis is the process in which water flows from an area with a low solute concentration, solute concentration, to an adjacent area with a higher solute concentration until equilibrium between the two areas is reached.[6] All cells are surrounded by a lipid bi-layer   cell cell membrane which permits the flow of water in and out of the cell while also limiting the flow of solutes. In hypertonic solutions, hypertonic solutions, water flows out of the cell which decreases the cell's volume. When in a hypotonic solution, hypotonic solution, water flows into the membrane and increases the cell's ce ll's volume. When in an isotonic solution, isotonic solution, water [4] flows in and out of the cell at an equal rate.   Turgidity is the point at which the cell's membrane pushes against the cell wall, which is when turgor pressure is high. When the cell membrane has low turgor pressure, it is flaccid. In plants, [7]

this is shown as wilted anatomical structures. This is more specifically known as plasmolysis.

The volume and geometry of the cell affects the value of turgor pressure, and how it can have an effect on the cell wall's plasticity. Studies have shown how h ow smaller cells experience a stronger [3] elastic change when compared to larger cells.   Turgor pressure also plays a key role in plant cell growth where the cell wall und undergoes ergoes irreversible expansion due to the force of turgor pressure p ressure as well as structural changes in the cell [8] wall that alter its extensibility.   Turgor pressure in plants and its importance

Turgor pressure within cells is regulated by osmosis and this also causes the cell wall to expand during growth. Along with size, rigidity of the cell is also caused by turgor pressure; a lower   pressure results in a wilted cell wilted cell or plant structure (i.e. leaf, stalk). One mechanism in plants that regulate turgor pressure is its semipermeable membrane, which only allows some solutes to travel in and out of the cell, which can also maintain a minimum amount of pressure. Other  mechanisms mechan isms include transpiration, transpiration, which results in water loss and decreases turgidity in cells. [9] Turgor pressure is also a large factor for nutrient transport throughout the plant. Cells of the same organism can have differing turgor pressures throughout the organism's structure. In higher   plants,, turgor  plants turgor pressure pressure is responsibl responsiblee for apical growth of growth of things such as root tips[10] and  and pollen  pollen [11] tubes..   tubes Plasmolysis   is the proces proc esss in whic h ce cell lo water water in solution a hypertonic  hypertonic   solution. The external reverse  process, cytolysis, cytolysis , can occur if which the cell isllssinlose ase hypotonic solution hypotonic resulting in a lower

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osmotic pressure  pressure  and a net flow of water into the cell. Through observation observation of plasmolysi plasmolysiss and deplasmolysis, it is possible to determine the tonicity of tonicity of the cell's environment as well as the rate solute molecules cross the cellular membrane. membrane.

  Before plasmolysis (top) and after (bottom)

 Topic: Absorption of water and minerals salts

The absorption of water by  by plants  plants is  is essential for various metabolic activities. Terrestrial plants get their water supply from soil which serves as the source of water and [minerals]. The way in which water from soil enters roots, particularly to the root xylem, is called "mechanism of water  absorption". Both active and passive absorption have been proposed for mechanism of water  absorption.This process is known as Conduction Active absorption

Active absorption Active absorption refers to the absorption absorption of water by roots with the help of ATP, ATP, generated by the root root respiration: respiration: as the the root root cells cells activ activel ely y ta take ke part part in the pr proce ocess ss,, it is ca call lled ed active absorption.. According to Renner, active absorption takes place in low transpiring and wellabsorption watered plants, and 4% of total water absorption is carried out in this process. The active absorption is carried out by two theories; active osmotic water absorption and Active nonosmotic water absorption. In this process energy is required.

 Active osmotic osmotic water absorption absorption This theory was given by Pari (1910) and Priestley (1921). According to this theory, the root cells behave as an ideal osmotic pressure system through which water moves up from the soil solution to the root xylem along xylem along an increasing gradient of D.P.D. (suction pressure, which is the real force for water absorption). If solute concentration is high and water potential is low in the roott cells, roo cells, water can enter enter from from soil soil to root root cells cells through through endosmosis. endosmosis. Mineral nutrients are absorb abs orbed ed activel actively y by the root cells due to utilis utilisati ation on of adenosine triphosphate  triphosphate  (ATP). As a

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result, the concentration of ions (osmotica) in the xylem vessels is more in comparison to the soil water. A concentration gradient is established between the root and the soil water. Hence, the solute potential of xylem water is more in comparison to that of soil and correspondingly water   potential is low than the soil water.If stated, water potential is comparatively positive in the soil water. This gradient of water potential causes endosmosis. The endosmosis of water continues till the water potential both in the root and soil becomes equal. It is the absorption of minerals that utilise metabolic energy, but not water absorption. Hence, absorption of water is indirectly an active process in a plant's life.Active transport is in an opposite direction to that of diffusion. [1]

 Active non-osmotic non-osmotic water absorption This theory This theory was given given by Thiman Thimann n (1951) (1951) and Kramer Kramer (1959). (1959). Accordi According ng to the theory theory,, sometimes somet imes water is absorbed against against a concentratio concentration n gradient. gradient. This requires requires expenditure expenditure of  metabolic energy released from respiration of root cells. There is no direct evidence, but some scientists suggest involvement of energy from respiration. In conclusion, it is said that, the evidences supporting active absorption of water are themselves poor.[2]  Passive absorption

This mechanism is carried out without utilisation of metabolic energy. Here, only the roots act as an organ of absorption or passage. Hence, sometimes it is called water absorption 'through roots', rather 'by' roots. It occurs in rapidly transpiring plants during the daytime, because of the opening of stomata and the atmospheric conditions. The force for absorption of water is created at the leaf  end i.e. the transpiration pull. The main cause behind this transpiration pull, water is lifted up in the plant axis like a bucket of water is lifted by a person from a well. Transpiration pull is responsible for dragging water at the leaf end, the pull or force is transmitted down to the root through column of water in the xylem elements. The continuity of the water column remains intact due to the cohesion between the molecules and it act as a rope. Roots simply act as a  passive organ of absorption. As transpiration proceeds, water absorption occurs simultaneously to compensate the water loss from the leaf end. Most volume of water entering plants is by means of passive absorption. Passive transport is no different from diffusion, it requires no input of energy: there is free movement of molecules from their higher concentration to their lower  concentration. The water will enter the plant via the root cells that can be found in the roots where whe re mainly mainly passiv passivee absorp absorptio tion n occurs occurs.. Also, Also, with with the absorp absorpti tion on of wat water, er, miner minerals als and nutrients are also absorbed.  Topic: Conduction of water and minerals salts Root pressure is the transverse osmotic pressure within the cells of a root system that causes sap to rise through a plant stem to the leaves.[1] 

Root pressure occurs in the xylem of xylem of some vascular plants when plants when the soil moisture level is high either at night ortension, when transpiration is transpiration low pressure, during thedue day. transpiration high, xylem sap is usually under rather than is under toWhen transpirational pull. pullis . At night in some

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 plants, root pressure causes guttation or guttation or exudation exudation of drops of xylem sap from the tips or edges of leaves. Root pressure is studied by removing the shoot of a plant near the soil level. Xylem sap will exude from the cut stem for stem for hours or days due to root pressure. If a pressure gauge is attached to the cut stem, the root pressure can be measured. Root press Root pressure ure is caused caused by active active distri distribut bution ion of minera minerall nutrie nutrient nt ions ions into into the root  root  xylem. Without transpiration to carry the ions up the stem, they accumulate in the root xylem and lower  the water potential. potential. Water then diffuses from the soil into the root xylem due to osmosis. osmosis. Root  pressure is caused by this accumulation of water in the xylem pushing on the rigid cells. Root  pressure provides a force, which pushes water up the stem, but it is not enough to account acc ount for the movement of water to leaves at the top of the tallest trees. trees. The maximum root pressure measured in some plants can raise water only to 6.87 meters, and the tallest trees are over 100 meters tall.

Topic: Transpiration

 movement through a plant a plant and  and its evaporation from evaporation from aerial parts, such as it is the process of water  movement leaves,, stems and leaves stems and flowers. flowers. Water is necessary for plants but only a small amount of water taken up by the roots is used for growth and metabolism. The remaining 97–99.5% is lost by transpiration and guttation. guttation.[1]  The thre The threee majo majorr types types of trans transpi pira rati tion on ar are: e: (1) (1) St Stom omat atal al Tr Tran ansp spir irat atio ion n (2 (2)) Le Lent ntic icul ular  ar  Transpiration and (3) Cuticular Transpiration. Transpiration mainly takes place through surface of leaves. It is known as Foliar transpiration (more than 90%). Transpiration occurs through young or mature stem is called as Cauline transpiration.

 Stomatal Transpiration: Transpiration: Water vapour diffuses out through minute pore (stomata) present in soft aerial part of plant is known as Stomatal Transpiration. Of the total water loosed, near about 85 – 90% of water loosed  by the stomatal transpiration.

Lenticular Transpiration: Transpiration: Sometimes water may evaporate through certain other openings present on the older stems. These openings are called Lenticels and the transpiration that takes place through term is known as Lenticular Transpiration. Cuticular transpiration:

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Loss of water may also take place through cuticle, but the amount so lost is relatively small and make up only about 5 to 10 percent of the total transpiration. This type of transpiration depends upon the thickness of the cuticle and presence or absence of wax coating on the surface of the leaves. Xerophytic plants generally have very thick cuticle and wax coating on the leaves and stem in order to check cuticular transpiration. Factor affecting transpiration

Feature

Effect on transpiration

 Number of leaves

More leaves (or spines, or other photosynthesizing organs) means a bigger surface area and more stomata for gaseous exchange. e xchange. This will result in greater water loss.

 Number of stomata

More stomata will provide more pores for transpiration.

Size of the leaf 

A leaf with a bigger surface area will transpire faster than a leaf with a smaller surface area.

Presence of  plant cuticle

A waxy cuticle is relatively impermeable to water and water vapour and reduces evaporation from the plant surface except via the stomata. A reflective cuticle will reduce solar heating and temperature rise of the leaf,[citation needed ] helping to reduce the rate of evaporation. Tiny hair-like structures called trichomes on trichomes on the surface of leaves also can inhibit water loss by creating a high humidity environment at the surface of leaves. [citation needed ] These are some examples of the adaptations of plants for conservation of water that may be found on many xerophytes.. xerophytes The rate of transpiration is controlled by stomatal aperture, and these small pores

Light supply

open especially for photosynthesis. While there are exceptions to this (such as night or "CAM "CAM photosynthesis"), photosynthesis"), in general a light supply will encourage open stomata. Temperature affects the rate in two ways:

Relative humidity

1) An increased rate of evaporation due to a temperature rise will hasten the loss of water. 2) Decreased relative relative humidity  humidity outside the leaf will increase the water potential water  potential gradient.. gradient Drier surroundings gives a steeper water potential gradient, and so increases the rate of transpiration.

Wind

In sti still ai airr, wat water er lost lost due due to to tra trans nspi pira rattion can can acc accum umul ulat atee in in the the for orm m of of vapo vaporr

Temperature

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close to the leaf surface. This will reduce the rate of water loss, as the water  potential gradient from inside to outside of the leaf is then slightly slightly less. Wind  blows away much of this water vapor near the leaf surface, making the potential gradient steeper and speeding up the diffusion of water molecules into the surrounding air. Even in wind, though, there may be some accumulation of water vapor in a thin boundary thin boundary layer  of  of slower moving air next to the leaf surface. The stronger the wind, the thinner this layer will tend to be, and the steeper the water  potential gradient. Water supply

Water stress caused stress caused by restricted water supply from the soil may result in stomatal closure and reduce the rates of transpiration.

 Significance o Transpiration: Transpiration: Several beneficial and harmful effects are ascribed to transpiration. Advantages: There are three possible advantages of transpiration to the plants and these are discussed below: I. Transport of minerals: 

Usually, Usuall y, high high trans transpir pirati ation on rates rates cause cause high high rates rates of minera minerall absorp absorptio tion. n. How Howeve ever, r, deep deep un under derst stan andi ding ng of diff diffus usio ion n and diff differ eren enti tial ally ly perme permeab able le memb membra rane ness point point to towa ward rdss th thee independent absorption of minerals. It is generally held that minerals absorbed by the plant from the soil usually move up through the  plant via transpiration stream. The quantum quantum of minera minerals ls reachi reaching ng the leaves is depende dependent nt upon upon the rate of absorp absorpti tion on of  minerals by the roots rather than the rate of transpiration. Rates of transpiration do not seem to affect the availability of minerals in the leaf. On the contrary when the mineral in the soil are in abundance then the rate of transpiration is vital for  their translocation. II. Lowering of leaf temperature:  

Transpiration of water from a surface of the leaf lowers the temperature of that organ since the loss of water molecules of a relatively high kinetic energy; the molecules having highest kinetic energy are the first to evaporate. Rough estima Rough estimates tes show show around around that that transp transpira iratio tion n removes removes about 600 calori calories es per gram gram of  evaporated water.

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There are other ways e.g., radiation and convection by which heat is removed. If transpiration stops, there would be an enhanced loss of heat by radiation and convection because of the increased leaf temperature. III. Optimum turgidity: 

It is generally argued that there is an optimum level of water potential within the plant. Many and an d varied functions are slowed down or are rendered inefficient both above and below this level. In the absence of transpiration, plants tend to become over turgid and will cease to grow. Similarly when the water potential becomes highly negative neg ative growth also stops. IV. Bringing water to the top of a plant:

It is also suggested that importance of transpiration is embodied in its essentiality to pull water to the top of the trees. Disadvantages:  

The conclusive fact about transpiration is that it is harmful. It is loss of one of the essential compon com ponent entss of life life and one of the substrat substrates es of most most import important ant process process for the plant plant lif lifee photosynthesis. It may be added that the existence of transpiration in plants may not no t be taken to mean that it is useful to the plant body. bo dy.

Guttation

exudation of drops of xylem sap xylem sap on the tips or edges of leaves of some vascular plants, plants, it is the exudation such uch as grasses  grasses  and a nu numb mber er of fungi fungi.. Gutt Guttat atio ion n is not to be confus confused ed with with dew, dew, which condenses from the atmosphere onto the plant surface. At night, night, transpiration usually transpiration usually does not occur, because most plan plants ts have their stomata  stomata  closed. When there is a high soil moisture moisture level,  level, water will enter plant roots, because the water potential of the roots is lower than in the soil solution. The water will accumulate in the plant, creating a sli slight ght root pressure. pressure. The root pressure forces some some water to exude through special leaf  tip   tip or  edge structures, hydathodes or hydathodes or water glands, forming drops. Root pressure provides pressure provides the impetus for this flow, rather than transpirational pull. pull. Guttation is most noticeable when transpiration is suppressed suppr essed and the relative relative humidity humidity is high, such as during the night. The process process of guttation guttation formation in fungi is unknown. Topic: Ascent of sap

The ascent of sap in the xylem tissue xylem tissue of plants is the upward movement of water and minerals from the root to root to the crown. Xylem is a complex tissue consisting of living and non-living cells.

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The conducting cells in xylem are typically non-living and include, in various groups of plants, vessels members and tracheids. Both of these cell types have thick, lignified secondary lignified secondary cell walls and are dead at maturity. Although several mechanisms have been proposed to explain the  phenomenon, the cohesion-tension mechanism[1] has the most evidence and support. Although cohesion-tension has received criticism, for example due to the apparent existence of large negati neg ative ve pressu pressures res in some some livin living g plants plants,, experi experiment mental al and observ observati ationa onall data data favor favor this this [2] [3] mechanism.   The more recently recently proposed compensating compensating pressure pressure (CP) theory favors favors a version version of vital theory  proposed by Jagdish Chandra Bose. Bose. However, experimental evidence has not supported it [4]  An alternative theory based on the behavior of thin films has been developed by Henri Gouin, a French professor of fluid dynamics. [5] The theory is intended to explain how water can reach the upperm upp ermost ost parts of the talles tallestt trees, trees, where where the applicabi applicabilit lity y of the cohesion-tension theory  theory  is [6] debatable.   The theory assumes that in the uppermost parts of the tallest trees, the vessels of the xylem  xylem  are coated with thin films of sap. The sap interacts physically with the walls of the vessels: as a result of van der Waals forces, forces, the density of the film varies with distance from the wall of a vessel. This variation density, in turn, pressure produces isa "disjoining "adisjoining pressure ", whose varies with distance from theinwall. (Disjoining differencepressure", in pressure fromvalue that which  prevails in the bulk of a liquid; it is due d ue to the liquid's interaction with a surface. The interaction may result in a pressure at the surface that is greater or less than that which prevails in the rest of  the liquid liquid.) .) As a tree's tree's leaves leaves transpire, transpire, water is drawn from the xylem's vessels; hence, the thickness of the film of sap varies with height within a vessel. Since the disjoining pressure varies var ies with the thickne thickness ss of the film, film, a gradie gradient nt in the disjoini disjoining ng pressu pressure re arises arises during transpiration: the disjoining pressure is greater at the bottom of the vessel (where the film is thickest) and less at the top of the vessel (where the film is thinner). This spatial difference in  pressure within the film results results in a net force that pushes the sap upwards towards the leaves. Topic: Manufacturing of food: Photosynthesis:

processs used by plants plants and other organis organisms ms to convert  convert  light energy  energy  into Photosynthesis   is a proces chemical energy that energy that can later be released to released to fuel the organisms' activities. This chemical energy is stored in carbohydrate molecules, molecules, such as sugars, sugars, which are synthesized synthesized from carbon dioxide and water  –   – hence the name photosynthesis name  photosynthesis,, from the the Greek   φῶς, φῶς,  phōs  phōs,, "light", and σύνθεσις, σύνθεσις, [1] [1][2] [2][3] [3]  synthesis,, "putting together".  synthesis   In most cases cases,, oxygen  oxygen  is also released as a waste product. Most plants Most  plants,, most algae, algae, and cyanobacteria  cyanobacteria  perform photosynthesis; such organisms are called  photoautotrophs.. Photosynthesis is largely responsible for producing and maintaining the oxygen  photoautotrophs content of content  of the Earth's atmosphere, and supplies all of the organic compounds and most of the energy necessary for life on Earth. Earth.[4]  Although photosynthesis is performed differently by different species, the process always begins when wh en ener energy gy from from light light is ab abso sorb rbed ed by  proteins   proteins  call called ed reaction reaction centres centres  that contain contain green

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chlorophyll  pigmen chlorophyll  pigments. ts. In plants plants,, these these proteins proteins are held inside inside organelles  organelles  calle called d chloroplasts, chloroplasts, which whi ch are most abundant abundant in leaf leaf cells, cells, while while in bacteria bacteria they are embedded embedded in the  plasma membrane.. In these light-dep membrane light-depende endent nt reaction reactions, s, some some energy energy is used used to strip strip electrons  electrons  from suitable substances, such as water, producing oxygen gas. The hydrogen freed by the splitting of  water is used in the creation of two further compounds that serve as short-term stores of energy, enabling its transfer to drive other reactions: these compounds are reduced nicotinamide adenine dinucleotide phosphate (NADPH) phosphate (NADPH) and adenosine triphosphate (ATP), triphosphate (ATP), the "energy currency" of  cells. In plants, algae and cyanobacteria, long-term energy storage in the form of sugars is produced by a subsequent sequence of light-independent reactions called the Calvin cycle; cycle; some bacteria use different mechanisms, such as the reverse Krebs cycle, cycle, to achieve the same end. In the Calvin cy cycl cle, e, atmo atmosp sphe heri ricc ca carb rbon on diox dioxid idee is incorporated  incorporated  int into o alr already eady existi existing ng organi organicc carbon carbon [5] compounds, such as ribulose bisphosphate (RuBP). bisphosphate (RuBP).  Using the ATP and NADPH produced by the light-dependent light-dependent reactions, reactions, the resulting resulting compounds are then reduced reduced and  and removed to form further carbohydrates, such as glucose. glucose. The first photosynthetic organisms probably evolved early evolved early in the evolutionary history of life and life  and mostt likel mos likely y used used reducing reducing agents  agents  such as hydrogen  hydrogen  or hydrogen sulfide, sulfide, rather than water, as [6]

sou source rcess of directly electr electrons ons.   Cyan Cy anob obact acter eria iaofap appea peare red d ,[7] la late ter; r; th theerendered exces excesss the ox oxyge ygen n th they eyofpr prod oduce uced d contributed to. the oxygenation the Earth, Earth  which evolution complex life   possi life possibl ble. e. Today Today,, the the avera average ge ra rate te of en ener ergy gy ca capt ptur uree by ph phot otos osynt ynthe hesi siss gl glob obal ally ly is [8][9] [9][10] [10] [8] approximately 130 terawatts, terawatts,  which is about three times the current power current power consumption of  [11] human civilization. civilization.  Photosynthetic organisms also convert around 100–115 billion tonnes (91[12][13]   104 petagrams 104  petagrams)) of carbon into biomass into  biomass per  per year.[12][13] chemosynthesis  :In biochemistry, chemosynthesis  is the biological conversion of one or more carbon-conta carbon -containing ining molecules (usually (usually carbon dioxide  dioxide  or methane) methane) and nutrients into organic matter mat ter using using the oxidation  oxidation  of inorganic compounds compounds (e.g., (e.g., hydrogen  hydrogen  gas, gas, hydrogen hydrogen sulfide sulfide)) or  methan met hanee as a source source of energy energy,, rather rather than sunligh sunlight, t, as in  photosynthesis.  photosynthesis. Chemoautotrophs Chemoautotrophs,, organisms   that obtain carbon through chemosynthesis, are phylogenetically diverse, but also organisms groups that include conspicuous or biogeochemically-important taxa include the sulfur-oxidizing

gamma and epsilon proteobacteria epsilon proteobacteria,, the Aquificae, Aquificae, the methanogenic archaea methanogenic archaea and the neutrophilic iron-oxidizing bacteria. Many microorganisms in dark regions of the oceans use chemosynthesis to produce biomass from single carbon molecules. Two categories can be distinguished. In the rare sites at which hydrogen molecules (H2) are available, the energy available from the reaction between CO 2 and H2  (leading to production of methane, CH 4) can be large enough to drive the production of   biomass. Alternatively, in most oceanic environments, energy for chemosynthesis derives from reactions in which substances such as hydrogen sulfide or sulfide or ammonia are ammonia are oxidized. This may occur  with or without the presence of oxygen. Topic: Translocation and storage of food:

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  In plants, food is prepared by the the leaves by the process of    photosynthesis. The food prepared  by the leaves is in the form of  simple sugars (glucose). No other   part of the plant can prepare food. So, all the parts of a plant require food for getting energy, maintenance and growth. That is why; wh y; the the food food prep prepar ared ed by the the leave le avess is tran transp spor orte ted d to al alll the the ot othe herr pa part rtss of a plan plantt thro throug ugh h  phloem. The transportation of  food from the leaves to other parts of the plant is called translocation. Why trans ranslo loca cattion ion of food ood is necessary for plants? The the food plant made is nby ecethe ssaryleaves to bof  e translocated to all the other parts of the plant so that every part of  the plant can utilize the food for  ob obta tain inin ing g en ener ergy gy as well well as for  for  growth and repair.  

Unit 7 plant cytology and genetics

branch ch of  biology   biology  co conc ncer erne ned d wi with th the stud study y of genes genes,, genetic variation, variation, and Genetics  is a bran [1][2][3] [1][2] [3]   heredity in heredity  in organisms. organisms. Heredity  is the the passi passing ng on of traits  traits  from from parent parentss to their their offspr offspring ing,, eit either her through through asexual reproduction   or sexual reproductio reproduction reproduction n, the the offs offspr prin ing g cells cells   or organisms  organisms  acqu acquiire the the genetic information of information  of their parents. Through heredity, variations between individuals can accumulate and cause species to species to evolve by evolve by natural selection. selection. The study of heredity in biology in  biology is  is genetics. genetics.

Gregor Mendel, Mendel, a scientist and Augustinian  Augustinian  friar , discovered genetics in the late 19th-century. Mendel studied "trait inheritance", patterns in the way traits are handed down from parents to offspring. He observed that organisms (pea plants) inherit traits by way of discrete "units of  inheritance". This term, still used today, is a somewhat ambiguous definition of what is referred to as a gene. gene.  Topic:

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type of  biological   biological  inheritance  inheritance  that follows the laws originally Mendelian inheritance Mendelian inheritance  is a typ  proposed by Gregor Mendel in Mendel in 1865 and 1866 and re-discovered in 1900. These laws were init in itia iall lly y co cont ntro rove vers rsia ial. l. When When Mend Mendel el's 's theor theorie iess were were in inte tegr grat ated ed wi with th th thee Boveri–Sutton chromosome theory of theory of inheritance by Thomas Hunt Morgan in Morgan in 1915, they became the core of  classical genetics. genetics. Ronald Fisher  combined   combined these ideas with the theory of natural selection in selection in his 19 1930 30 book The Genetical Theory of Natural Selection, Selection , putting putting evolution  evolution  onto a mathematical footing and forming the basis for population for population genetics within genetics within the modern evolutionary synthesis. synthesis.[1] A  monohybrid cross  is a ma mati ting ng betw betwee een n tw two o or orga gani nism sms s wi with th [1] [1][2] different variations at one genetic chromosome of interest. [2] The character(s) being studied in a monohybrid cross are governed by two or multiple variations for a single locus.

A cross between two parents possessing a pair of contrasting characters is known as monohybrid homozygous or  or true breeding breeding for a cross. To carry out such a cross, each parent is chosen to be homozygous given trait (locus). trait (locus). When a cross satisfies the conditions for a monohybrid cross, it is usually detected by a characteristic distribution of second-generation (F 2) offspring that is sometimes called the monohybrid ratio. Law Dominance Mendel's cross of ration. parentsOffspring that are pure onlyhave one form of the traitofwill appear in “In the anext generation. gene that for are contrasting hybrid for hybrid for atraits, trait will only the dominant trait in the phenotype.”

Definition. Law of segregation. During gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene. Dihybrid cross is a cross between two different lines/genes that differ in two observed traits. traits . According to Mendel's statement, between the alleles of both these loci there is a relationship of  complete dominance - recessive. In the example pictured to the right, RRYY/rryy parents result in F1 offspring that are heterozygous for heterozygous for both R and Y (RrYy). [1] 

Law of independent assortment. Genes for different traits can segregate  independently during the formation of gametes.

hybrid with one of its parents its  parents or  or an individual genetically similar  Backcrossing is a crossing of a hybrid with to its parent, in order to achieve offspring with a genetic identity which is closer to that of the  parent. It is used in horticulture, animal breeding and in production of gene knockout organisms. knockout organisms. In genet genetic ics, s, a test cross first introd introduced uced by Gregor Gregor Mendel, Mendel, involv involves es the breeding breeding of an cross, first individual indiv idual with a phenotypical phenotypically ly recessive recessive individual, individual, in order to determine determine the zygosity zygosity of the former by analyzing proportions of offspring phenotypes. Zygosity can either be heterozygous or  homozygous. Non-Mendelian inheritance

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In four o'clock plants, the alleles for red and white flowers show incomplete dominance. As seen in the F1 generation, heterozygous (wr  ( wr ) plants have "pink" flowers—a mix of "red" (rr) and "white" (ww) coloring. The F 2 generation shows a 1:2:1 ratio of red:pink:white Main article: Non-Mendelian article: Non-Mendelian inheritance Mendel explained inheritance in terms of discrete factors—genes—that are passed along from generation to generation according to the rules of probability. Mendel's laws are valid for all sexually reproducing organisms, including garden peas and human beings. However, Mendel's laws stop short of explaining some patterns of genetic inheritance. For most sexually reproducing organisms, cases where Mendel's laws can strictly account for the patterns of inheritance are relatively rare. Often, the inheritance patterns are more complex. The F1 offspring of Mendel's pea crosses always looked like one of the two parental varieties. In this situation of "complete dominance," the dominant allele had the same phenotypic effect whether present in one or two copies. But for some characteristics, the F 1  hybrids have an appearance in between the between the phenotypes of the two parental varieties. A cross between two four  o'clock ( Mirabilis  Mirabilis jalapa) jalapa) plants shows this common exception to Mendel's principles. Some alleles allel es are neither neither dominant dominant nor recessive. recessive. The F 1 generation produced by a cross between redflow flower ered ed (R (RR) R) an and d whit whitee flow flower ered ed (WW) (WW)  Mirabilis jalapa  jalapa  plant plantss consists consists of pink-color pink-colored ed flowers (RW). Which allele is dominant in this case? Neither one. This third phenotype results from flowers of the heterzygote having less red pigment than the red homozygotes. Cases in which one allele is not completely dominant over another are called incomplete dominance. In incom in compl plet etee domin dominan ance ce,, the the heter heteroz ozyg ygous ous ph phen enot otyp ypee li lies es so some mewh wher eree betwe between en th thee tw two o homozygous phenotypes. A similar situation arises from codominance, in which the phenotypes produced by both alleles are clearly expressed. For example, in certain varieties of chicken chicken,, the allele for black feathers is codominant with the allele for white feathers. Heterozygous chickens have a color described as "erminette", speckled with black and white feathers. Unlike the blending of red and white colors in heterozygous four o'clocks, black and white colors appear separately in chickens. Many human genes, including one for a protein that controls cholesterol levels in the blood, show codominance, codomi nance, too. People with the heterozygous heterozygous form of this gene produce two different different forms of the protein, each with a different effect on cholesterol levels. In Mendelian inheritance, genes have only two alleles, such as a  and A and  A.. In nature, such genes exist in several different forms and are therefore said to have multiple alleles. A gene with more than two alleles is said to have multiple alleles. An individual, of course, usually has only two copies of each gene, but many different alleles are often found within a population. One of the  best-known examples is coat color in rabbits. A rabbit's coat color co lor is determined by a single gene that has at least four different alleles. The four known alleles display a pattern of simple dominance that can produce four coat colors. Many other genes have multiple alleles, including the human genes for ABO blood type. type. Furthermore, Furthermor e, many traits are produced produced by the interaction interaction of several several genes. Traits controlled controlled by two or more genes are said to be polygenic traits. Polygenic  Polygenic means  means "many genes." For example, at least three genes are involved in making the reddish-brown pigment in the eyes of fruit flies.

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Polygenic traits often show a wide range of phenotypes. The broad variety of skin color in humans comes about partly because at least four different genes probably control this trait. Monogenic inheritance refers to the kind of inheritance  whereby a trait is determined by the expres exp ressio sion n of a single single gene or allele allele,, not by severa severall genes genes as in polygen polygenic ic inheritance. ... A disease or or monogenic disorder would thus result when a single pair of genes is monogenic  disease involved. Synonym(s): Mendelian inheritance.Jul 31, 2017 Gene 

In biology In  biology,, a gene is a sequence of nucleotides in DNA  DNA  or RNA that RNA that codes for codes for a molecule that expression,, the DNA is first copied into RNA. RNA. The RNA can be has a functi function. on. During During gene expression directly functional  template  for a protein a  protein that  that performs a function. The functional  or be the intermediate template  offspring   is the basis of the inherit inheritance ance of  phenotypic transmiss trans mission ion of genes to an organism's organism's offspring trait.. These genes make up different DNA sequences trait sequences called genotypes. genotypes. Genotypes along with enviro env ironme nmenta ntall and develop developmen mental tal factor factorss determ determine ine what what the phenoty phenotypes pes will will be. Most Most  biological traits are under the influence of  polygenes  polygenes (many  (many different genes) as well as gene–  environment interactions. interactions. Some genetic traits are instantly visible, such as eye color  or   or number  type,, risk for specific diseases, or the thousands of  of limbs, and some are not, such as  blood type  basic biochemical processes  basic biochemical  processes that constitute life. life. Deoxyribonucleic Deoxyribonucle ic acid is a molecule composed of two chains that coil around each other to form a double double helix helix   ca carr rryi ying ng the the genetic  genetic  instru instructi ctions ons used used in the growth growth,, develop developmen ment, t, functi fun ctioni oning, ng, and reproduction  reproduction  of all all kn know own n livi living ng organisms  organisms  and man many y viruses. viruses. DNA and ribonucleic acid (RNA) acid (RNA) are nucleic acids; acids; alongside proteins alongside proteins,, lipids and lipids and complex carbohydrates ( polysaccharides),  polysaccharides), nucleic nucleic acids acids are one of the four major major types of macromolecules  macromolecules  that are essential for all known forms of life. life.

The tw The two o DNA DNA stra strands nds are also also kn know own n as  polynucleotides   polynucleotides  as they are composed of simpler  [2] [2][3] [3] monomeric   units called monomeric called nucleotides. nucleotides.  Each nucleotide is composed of one of four nitrogencontaining   nucleobases  containing nucleobases  (cytosine [C], cytosine [C], guanine [G], guanine [G], adenine [A] adenine [A] or thymine [T]), thymine [T]), a sugar  called   called deoxyribose,, and a phosphate deoxyribose a  phosphate group. group. The nucleotides are joined to one another in a chain by covalent bonds between bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. backbone. The nitrogenous bases of the two separate polynucleotide str strands ands are bound bound togeth together, er, according according to  base pairing rules pairing rules (A with T and C with G), with hydrogen bonds to bonds to make double-stranded DNA. The complementary complementary nitrogeno nitrogenous us bases are divided into two groups, groups, pyrimidines  pyrimidines and  and purines  purines.. In DNA, the pyrimidines are thymine and cytosine; the purines are adenine and guanine. Both strands of double-stranded DNA store the same biological information. information. This information is replicated as and when the two strands separate. A large part of DNA (more than 98% for  huma humans ns)) is non-coding, non-coding, meani meaning ng that that thes thesee se sect ctio ions ns do no nott se serv rvee as pa patt tter erns ns fo forr pr prot otei ein n sequences.

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The two strands strands of DNA run in opposi opposite te directio directions ns to each each other other and are thus antiparallel. antiparallel. Attached to each sugar is one of four types of nucleobases (informally, bases bases). ). It is the sequence of these four nucleobases along the backbone that encodes genetic information. RNA strands RNA strands are create cre ated d using using DNA strands strands as a templa template te in a proces processs called called transcription. transcription. Under Under the genetic code,, these RNA strands specify the sequence of amino acids within code acids within proteins in a process called translation.. translation Within Withi n eukary eukaryoti oticc cells, cells, DNA is organi organized zed into into long long str struct ucture uress called called chromosomes. chromosomes. Before typi ty pica call cell division, division, these these chromosom chromosomes es are duplica duplicated ted in the process process of DNA replication, replication,  providing a complete set of chromosomes for each daughter cell. Eukaryotic organisms ( organisms (animals animals,,  plants,, fungi and  plants fungi and protists  protists)) store most of their DNA inside the cell nucleus and nucleus and some in organelles, organelles, [4] such as mitochondria or mitochondria or chloroplasts. chloroplasts.  In contrast, prokaryotes contrast,  prokaryotes (  ( bacteria and  bacteria and archaea) archaea) store their  DNA DN A only only in the cytoplasm. cytoplasm. Within Within eukaryo eukaryoti ticc chromo chromosom somes, es, chromatin  chromatin  protei proteins, ns, such as histones,, compact histones compact and organize DNA. These compact structures structures guide the interaction interactionss between between DNA and other proteins, helping control which parts of the DNA are transcribed. a polymeric molecule  molecule essential in various biological roles in coding, coding, Ribonucleic acid ( RNA) is a polymeric decoding,, regulation and decoding regulation and expression of expression of genes. genes. RNA and DNA are DNA are nucleic acids, acids, and, along with lipids,,  proteins  lipids  proteins  and and carbohydrates, carbohydrates, constit constitute ute the four four major major macromolecules  macromolecules  essential for all known forms of life. life. Like DNA, RNA is assembled as a chain of nucleotides, nucleotides, but unlike DNA it is more often found in nature as a single-strand folded onto itself, rather than a paired doublestrand. Cellular organisms use messenger RNA  RNA  (mRNA) to convey genetic information (using the nitrogenous bases  bases  of guanine, guanine, uracil, uracil, adenine, adenine, and cytosine, cytosine, denoted by the letters G, U, A, and C) that directs synthesis of specific proteins. Many viruses encode viruses encode their genetic information using an RNA genome. genome. Comparison with DNA

Three-dimensional representation of the 50S 50S ribosomal  ribosomal subunit. Ribosomal RNA is in ochre,  proteins in blue. The active site is a small segment of rRNA, indicated indicated in red. The chemical structure of RNA is very similar to that of DNA, DNA, but differs in three primary ways: 





Unlike double-stranded DNA, RNA is a single-stranded molecule [1] in many of its  biological roles and consists of a much shorter chain of nucleotides.[2] However, RNA can, by complementary base pairing, form intrastrand (i.e., single-strand) double helixes, as in tRNA. While the sugar-phosphate "backbone" of DNA contains deoxyribose deoxyribose,, RNA contains [3] ribose instead. ribose  instead.  Ribose has a hydroxyl group hydroxyl group attached to the pentose ring in the 2'  2'   position, whereas deoxyribose does not. The hydroxyl groups in the ribose backbone make RNA less stable than DNA because it is more prone to hydrolysis. hydrolysis. The complementary base to adenine in adenine in DNA is thymine, thymine, whereas in RNA, it is uracil uracil,, [4] which is an unmethylated form unmethylated form of thymine.

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DNA replication DNA replica replicatio tion: n: The double helix  helix  is un'zip un'zipped ped'' and unwound unwound,, the then n each each separa separated ted str strand and (turquoise) acts as a template for replicating a new partner p artner strand (green). Nucleotides (green).  Nucleotides (bases)  (bases) are matched to synthesize the new partner strands into two new double helices. In molecular molecular biology biology,, DNA replication  is the the  biological process  process  of producing two identical replicas of DNA from one original DNA molecule DNA molecule and occurs in all living organisms acting organisms acting as the basis for biological for  biological inheritance. inheritance. The cell possesses the distinctive property of division, which makes replication of DNA essential. DNA is made DNA made up of a double helix  helix  of two two complementary  complementary  strands. strands. During replication, these strands are separated. Each strand of the original DNA molecule then serves as a template for the  production of its counterpart, a process referred to as semiconservative replication. replication. As a result of  semi-conservative replication, the new helix will be composed of an original DNA strand as well as a newly synthesized strand.[1]  Cellular Cellular  proofreading   proofreading  and error-checking  error-checking  mechanisms ensure [2][3] [2][3] near perfect fidelity for fidelity for DNA replication.   In a cell, cell, DNA replication begins at specific locations, or origins of replication replication,, in the genome. genome.[4] Unwinding of icas DNA atsult the and synthesis new strands, accommodated enzyme kn know own n as helic hel ase, e, re resu ltss origin in replicatio repli cation n forks  forks ofgrowin gro wing g bi-dir bi-direct ection ionall ally y from from by theanorigin ori gin.. A numb number er of  proteins   proteins  ar aree as asso soci ciat ated ed wi with th the the re repl plic icat atio ion n fo fork rk to help help in th thee in init itia iati tion on an and d continuation of DNA synthesis. synthesis. Most prominently, DNA polymerase synthesizes polymerase synthesizes the new strands  by adding nucleotides  nucleotides  that complement complement each (template) (template) strand. strand. DNA replicatio replication n occurs during the S-stage of interphase. interphase. DNA replication (DNA amplification) can also be performed in vitro (artificially, vitro (artificially, outside a cell). DNA polymerases isolated from cells and artificial DNA primers can be used to initiate DNA synthesis at known sequences in a template DNA molecule. Polymerase chain reaction (PCR), reaction (PCR), ligase chain reaction (LCR), reaction (LCR), and transcription-mediated amplification (TMA) amplification (TMA) are examples. first step step of gene expression, expression, in which which a partic particula ularr segmen segmentt of DNA  DNA  is Transcription   is the first copied into RNA (especially RNA (especially mRNA) mRNA) by the enzyme  enzyme  RNA polymerase. polymerase. Both DNA and RNA are nucleic acids, nucleic acids, whic hich use  base pairs  pairs  of nucleotides  nucleotides  as a complementary complementary   language. language. During trans ranscr criipti ption, on, a DN DNA A seque equenc ncee is read ead by an RNA RNA poly polym mer eras ase, e, whic which h pr prod oduc uces es a complementary, antiparallel RNA antiparallel RNA strand called a primary a  primary transcript transcript.. Mutation 

In biology In  biology,, a mutation is the permanent permanent alteration alteration of the nucleotide sequence of sequence of the genome of  genome of  [1] an organism, organism, virus, virus, or extrachromosomal DNA or DNA or other genetic elements.   Mutations result from error Mutations errorss during during DNA replication (especially replication (especially during meiosis) meiosis) or other types of damage to DNA (such DNA (such as may be caused by exposure to radiation or carcinogens carcinogens), ), which then [2] may undergo error-prone repair (especially microhomology-mediated end joining ), or cause an [3][4] [4] error during other forms of repair, [3]  or else may cause an error during during replication replication (translesion ( translesion synthesis). synthesis ). Mutation Mutationss may also result result from from insertion  insertion  or deletion of deletion of segments of DNA due to

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[5][6] [6][7] [7]   Mutations may or may not produce discernible changes in the mobile genetic elements. elements.[5] observable characteristics ( phenotype  phenotype)) of an organism. Mutations play a part in both normal and abnormal biological processes including: evolution, evolution, cancer , and the development development of the immune system,, including junctional system including junctional diversity. diversity.

The genomes of RNA viruses viruses are  are based on RNA rather RNA rather than DNA. The RNA viral genome can  be double stranded (as in DNA) or single stranded. In some of these viruses (such as the single strande ded d human human immunod immunodefi eficie ciency ncy virus virus)) re repl plic icat atio ion n oc occu curs rs quic quickl kly y an and d th ther eree ar aree no mechan mec hanism ismss to check check the genome genome for accura accuracy. cy. This This errorerror-pro prone ne proces processs often often result resultss in mutations. Significance

Mutation can result in many different Mutation different types of change in sequences. sequences. Mutations Mutations in genes  genes  can eitherr have no effect, alter the product eithe the  product of a gene, gene, or prevent the gene from functioning properly or completely. completely. Mutations Mutations can also occur in nongenic nongenic regions regions.. One study on genetic variations  between different species  species  of Drosophila of  Drosophila suggests  suggests that, if a mutation changes a protein a  protein produced  produced  by a gene, the result is likely to be harmful, with an estimated 70 percent of amino acid  polymorphisms that  polymorphisms  that have damaging effects, and the remainder being either neutral or marginally [8]

 beneficial.   Due to the damaging effects that mutations can have on genes, organisms have mecha me chani nism smss su such ch as DNA repair   to prevent or correct mutations by reverting the mutated sequence back to its original state. [5]  Chromosomal crossover

  (or crossing over) is the exchang exchangee of genetic genetic material material between between 2 homologous chromosomes non-sister chromatids that chromatids that results in recombinant chromosomes during chromosomes during sexual reproduction. reproduction. It is one one of the final final phase phasess of genetic genetic recombinati recombination on,, whic which h oc occu curs rs in th thee  pachytene  pachytene   stage of   prophase I of I  of meiosis during meiosis during a process called synapsis. synapsis. Synapsis begins before the synaptonemal complex develops complex  develops and is not completed until near the end of prophase I. Crossover usually occurs when matching regions on matching chromosomes break and then reconnect to the other  chromosome. Genome

It is the the genetic material material of an organism. It consists of DNA  DNA  (or RNA  RNA  in RNA viruses). viruses). The [1] genome gen ome includes includes both the genes  genes  (th (thee coding regions) regions) and and the the noncoding DNA, DNA,   as well as [2] mitochondrial DNA  and chloroplast DNA. DNA. The study of the genome is called genomics. genomics.  Topic: Plant breeding breeding  is the scienc sciencee of changi changing ng the the trai traits ts of  plants   plants  in order to produce desired [1] characteristics.  It has been used to improve the quality of nutrition in products for humans and animals.[2] Plant breeding can be accomplished through many different techniques ranging from simply selecting plants with desirable characteristics for propagation, to methods that make use of knowledge of genetics and chromosomes, to more complex molecular techniques (see cultigen

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and cultivar )).. Genes in a plant are what determine what type of qualitative or quantitative traits it will have. Plant breeders strive to create create a specific specific outcome of plants plants and potentially potentially new plant [2] varieties.   Plant breeding has been practiced for thousands of years, since near the beginning of human civilization. It is practiced worldwide by individuals such as gardeners and farmers, and by  professional plant breeders employed by organizations such as government  government  institutions, universities, crop-specific industry associations or research centers. Objective of plant breeding:

Traits that breeders have tried to incorporate into crop plants include: 1. Improved quality quality,, such as increased nutrition, improved flavor, or greater beauty yield of  of the crop 2. Increased yield 3. Increased tolerance tolerance of  of environmental pressures (salinity (salinity,, extreme temperature, temperature, drought drought)) viruses,, fungi and fungi and bacteria  bacteria 4. Resi Resist stan ance ce to to viruses 5. Incr Increa ease sed d tol toler eranc ancee to insect pests insect pests 6. Incr Increa ease sed d tol toler eranc ancee of herbicides

 A. Early techniques

Plant breeding started with sedentary agriculture and particularly the domestication of the first agricultural plants, agricultural  plants, a practice which is estimated to date back 9,000 to 11,000 years. [3] Initially early farmers simply selected food plants with particular desirable characteristics, and employed these as progenitors as progenitors for  for subsequent generations, resulting in an accumulation of valuable traits over time. 1. 1.Grafting Grafting technology had been practiced in China before 2000 BCE. [4] 

By 500 BCE grafting was well established and practiced. [5]  Gregor Mendel (1822–84) Mendel (1822–84) is considered the "father of modern genetics". genetics". His experiments with  plant hybridization  hybridization  led to his establishing establishing laws of inheritance. inheritance. Genetics stimulated research to improve crop production through plant breeding. Modern plant breeding is applied genetics, but its scientific basis is broader, covering molecular   biology,, cytology,  biology cytology, systematics, systematics,  physiology,  physiology,  pathology,  pathology, entomology, entomology, chemistry, chemistry, a nd nd statistics ( biometrics).  biometrics). It has also developed its own technology.

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2. Selection Selection  One major technique of plant breeding is selection, the process of selectively  propagating plants with desirable characteristics and eliminating or "culling" those with less desirable characteristics.[6]  3. Interbreeding: Another technique is the deliberate interbreeding ( crossing) of closely or  distantly related individuals to produce new crop varieties or lines with desirable properties. Plants Pla nts are crossb crossbred red to introd introduce uce traits/ traits/genes  genes  from one variety or line into a new genetic sistan tantt  pea  pea   may be crossed with a high-yielding but  background. For example, a mildew-re mildew-resis susceptible pea, the goal of the cross being to introduce mildew resistance without losing the high-yield characteristics. Progeny from the cross would then be crossed with the high-yielding  parent to ensure that the progeny were most like the high-yielding parent, ( backcrossing ). The  progeny from that cross would then be tested for yield (selection, as described above) and mildew resistance and high-yielding resistant plants would be further developed. Plants may also  be crossed with themselves to produce inbred  variet varieties ies for breedi breeding. ng. Pollin Pollinato ators rs may be excluded through the use of pollination excluded through of pollination bags. bags.

recombinati ination on   bet between ween chromo chromosom somes es to Cl Clas assi sica call bree breedi ding ng re reli lies es la larg rgel ely y on homologous homologous recomb generate genetic diversity diversity.. The classical plant breeder may also make use of a number of in vitro fusion,, embryo rescue  rescue  or mutagenesis  mutagenesis  (see below) to generate techni tec hniques ques such such as  protoplast fusion diversity and produce hybrid plants that would not exist in nature. nature. Modern plant breeding

Modern plant breeding may use techniques of molecular biology to select, or in the case of  geneticc modificati geneti modification, on, to insert, insert, desirable desirable traits traits into plants. Application Application of biotechnolog biotechnology y or  molecular biology is also known as molecular breeding. breeding.

Modern facilities in molecular biology are now used in plant breeding. 1. Marker assisted selection

Sometimes many different genes can influence a desirable trait in plant breeding. The use of  tools such as molecular markers or markers or DNA fingerprinting fingerprinting can  can map thousands of genes. This allows  plant breeders to screen large populations of plants p lants for those that possess the trait of interest. The screening is based on the presence or absence of a certain gene as determined by laboratory  procedures, rather than on the visual identification of the expressed trait in the plant. The purpose of marker assisted selection, selection, or plant genomes genomes analysis, analysis, is to identify the location location and function function ( phenotype)  phenotype) of various genes within the genome. If all of the genes are identified it leads to sequence. All plants have varying sizes and lengths of genomes with genes that code for  Genome sequence. different proteins, but many are also the same. If a gene's location and function is identified in one plant species, a very similar gene likely can also be found in a similar location in another  species genome.[10]  Reverse breeding and doubled haploids (DH)

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]

Homozygous plants  plants with desirable traits can be produced from heterozygous starting heterozygous starting plants, if a Homozygous haploid cell with the alleles for those traits can be produced, and then used to make a doubled haploid.. The double haploid doubled d haploid haploid will will be homozyg homozygous ous for the desire desired d tr trait aits. s. Furthe Furthermo rmore, re, two differ dif ferent ent homoz homozygo ygous us plants plants created created in that that way can be used used to produc producee a generat generation ion of F1 hybrid plants hybrid  plants which have the advantages of heterozygosity and a greater range of possible traits. Thus, an individual heterozygous plant chosen for its desirable characteristics can be converted into a heterozygous variety (F1 hybrid) without the necessity of vegetative reproduction but reproduction but as the result of the cross of two homozygous/doubled haploid lines derived from the originally selected plant.[11]  Using Using plant tissue culturing culturing can produce produce haploid haploid or double haploid plant lines and generations. This minimizes the amount of genetic diversity among that plant species in order to select for desirable traits that will increase the fitness of the individuals. Using this method decreases the need for breeding multiple generations of plants to get a generation that is homologous for the desired traits, therefore save much time in the process. There are many plant ti tissu ssuee cultur culturing ing techni techniques ques that can be used used to achieve achieve the haploi haploid d plants plants,, but micros microspor poree [10] culturing is currently the most promising for producing the largest numbers of them.   Genetic modification Transgenic plants

Genetic modification of modification of plants is achieved by adding a specific gene or genes to a plant, or by knocking down a gene with RNAi, RNAi, to produce a desirable phenotype desirable  phenotype.. The plants resulting from adding a gene are often referred to as transgenic plants. plants. If for genetic modification genes of the species or of a crossable plant are used under control of their native promoter, then they are called cisgenic plants. plants. Sometimes genetic modification can produce a plant with the desired trait or traits faster than classical breeding because the majority of the plant's genome is not altered. 1. What is monohybrid cross? Explain it and state law derived from this crosss.10 2. Explain Mendel’ law of independent assortment with help of dihybrid cross10 3.What are non-Mendelian inheritance? Describe10 4. What is plant breeding? Describe different tecniques10 5. Compare and contrast DNA and RNA.5 6 .What is mutation and crossing over? Write their significances.5 7 .Write Note on 5+5 1. DNA DNA repl replic icat atio ion n 2. Geno Genom me and and GENE GENE

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