Current Affairs 11th Class

It was developed by the Bragg (1913). They can be used as a tool for determining the arrangement of atoms in various biological molecules. When the X-rays pass through a molecule, they are scattered by the atoms. The diffraction pattern of the X?rays is photographed. Wavelength of X-rays is \[{{1}^{10}}{AA}.\] The nature of diffraction is related to the orientation of the atoms in the molecule. By using this technique Wilkins et al., 1953 found out details of the DNA molecule for which he was also awarded Nobel Prize along with Watson and Crick in 1962. Kendrew, 1957 by using the same technique studied the molecules of myoglobin.

Macromolecules are polymerisation product of micromolecuels, have high molecular weight and low solubility. They include mainly polysaccharide, protein and nucleic acids. (1) Polysaccharide : They are branched or unbranched polymers of monosaccharides jointed by glycosidic bond.  Their general formula is \[{{({{C}_{6}}{{H}_{10}}{{O}_{5}})}_{n}}.\] Polysaccharides are amorphous, tasteless and insoluble or only slightly soluble in water and can be easily hydrolysed to monosaccharide units. Types of polysaccharides (i) On the basis of structure Homopolysaccharides : These are made by polymerisation of single kind of monosaccharides. e.g., starch, cellulose, glycogen, etc. Heteropolysaccharide : These are made by condensation of two or more kinds of monosaccharides. e.g., chitin, pectin, etc. (ii) On the basis of functions Food storage polysaccharides : They serve as reserve food. e.g., starch and glycogen. Structural polysaccharides : These take part in structural framework of cell wall e.g., chitin and cellulose. Description of some polysaccharides Glycogen : It is a branched polymer of glucose and contain 30,000 glucose units. It is also called animal starch. It is also found as storage product in blue green algae, slime moulds, fungi and bacteria. It is a non-reducing sugar and gives red colour with iodine. In glycogen, glucose molecule are linked by \[14\] glycosidic linkage in straight part and \[16\] linkage in the branching part glycogen has branch points about every \[8-10\] glucose units. Starch : Starch is formed in photosynthesis and function as energy storing substance. It is found abundantly in rice, wheat, legumes, potato (oval and ecentric shaped), banana, etc. Starch is of two types. Straight chain polysaccharides known as amylose and branched chain as amylopectin. Both composed of \[D\]glucose units jointed by \[\alpha -1-4\] linkage and \[\alpha -1-6\] linkage. It is insoluble in water and gives blue colour when treated with iodine. Inulin : Also called “dahlia starch”(found in roots). It has unbranched chain of 30 – 35 fructose units linked by \[\beta -2-1\] glycosidic linkage between 1 and 2 of carbon atom of D– fructose unit. Cellulose : An important constituent of cell wall \[(2040%),\] made up of unbranched chain of \[6000\,\beta D\]glucose units linked by 1 – 4 glycosidic linkage. It is fibrous, rigid and insoluble in water. It doesn’t give any colour when treated with iodine. It is a most abundant polysaccharide. Chitin : It is a polyglycol consisting of \[N-\]acetyl\[D\]glucosamine units connected with \[\beta -1,\,4\] glycosidic linkage. Mostly it is found in hard exoskeleton of insects and crustaceans and some times in fungal cell wall. Second most abundant carbohydrate. It is a most abundant heteropolysaccharide. Agar-Agar : It is a galactan, consisting of both D and L galactose and it is used to prepare bacterial cultures. It is also used as luxative and obtained from cell wall of red algae e.g., Gracilaria, Gelidium etc. Pectin : It is a cell wall material in collenchyma tissue may also be found in fruit pulps, rind of citrus fruits etc. It is water soluble and can undergo sol \[\rightleftharpoons \] gel transformation. It contain arabinose, galactose and galacturonic acid. Neutral more...

These are molecules of low molecular weight and have higher solubility. These include minerals, water, amino acid, sugars and nucleotides. All molecules or chemicals functional in life activity are called biomolecules. (1) Elements : On the basis of presence and requirement in plants and animals, they are grouped into major \[(Ca,P,Na,Mg,S,K,N)\] and minor \[(Fe,Cu,Co,Mn,Mo,Zn,I)\] bioelements. On the basis of function, they may be of following types :– (i) Framework elements : Carbon, oxygen and hydrogen. (ii) Protoplasmic elements : Protein, nucleic acid, lipids, chlorophyll, enzymes, etc. (iii) Balancing elements : Ca, Mg and K. (2) Biological compounds (i) Inorganic compounds : Water 80%, inorganic salts 1-3%. (ii) Organic compounds : Carbohydrates (1.0%), Lipids (3.5%), Proteins (12.0%) Nucleotides (2.0%), Other compounds (0.5). (3) Cellular pool : Aggregated and interlinked  various kinds of biomolecules in a living system. So cell is called cellular pool. It includes over 5000 chemicals. Inorganic chemicals are present mostly in aqueous phase while organic in both, aqueous and non-aqueous. Cellular pool comprises of both crystelloid and colloidal particles. Hence called as crystal colloids. (4) Water : Liquid of life, major constituent of cell (about 60-90%) and exists in intracellular, intercellular and in vacuoles. In cells it occurs in free state or bound state (KOH, CaOH etc.). Properties of water : It is colourless, transparent, tastless and odourless, neutral (pH-7) liquid.  It is universal solvent, as it can dissolve both polar and non-polar solutes. High boiling point due to hydrogen bonding. Shows high degree of cohesion and adhesion. It can undergo three states of matter i.e., solid\[\rightleftharpoons \]liquid\[\rightleftharpoons \]gas.  It is dense and heaviest at 4C and solid below it. (5) Carbohydrates : e.g., sugars, glycogen (animal starch), plant starch and cellulose. Source of carbohydrate : Mainly photosynthesis. It exists only in 1% but constitutes 80% of the dry weight of plants. Composition : It consists of carbon, hydrogen and oxygen in the ratio \[{{C}_{n}}{{H}_{2n}}{{O}_{n}}.\] It is also called saccharide and sugars are their basic components. Classification of carbohydrates are : (i) Monosaccharides : These are single sugar units which can not be hydrolysed furthur into smaller carbohydrates. General formula is \[{{C}_{n}}{{H}_{2n}}{{O}_{n}},\]e.g., Trioses-3C, (Glyceraldehyde, dihydroxyacetone etc.), tetroses-4C, pentoses-5C, hexoses-6C etc. Important Hexoses Glucose : \[{{C}_{6}}{{H}_{12}}{{O}_{6}}.\] Grape sugar is dextrose. Grape is sour due to presence of tartaric acid. Fructose is called fruit sugar (sweetest among natural sugars) and glucose is called "sugar of body" (blood sugar). Normal level of blood glucose is 80-120mg/100ml. If it exceeds then condition is called "glucosuria". Fructose : Occurs naturally in fruit juices and honey. Hydrolysis of cane sugar in body also yields fructose. Galactose : It is called as brain sugar. It's an important constituent of glycolipids and glycoproteins. Properties of monosaccharide

• Monosaccharides are colourless, sweet tasting, solids and show oxidation, esterification and fermentation.
• Due to asymmetric carbon, they exist in different isomeric forms. They can rotate polarized light hence they are dextrorotatory and laevorotatory.
• D-glucose after reduction gives rise to a mixture of polyhydroxy alcohol, sorbitol or mannitol.
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Nucleic acids are the polymers of nucleotide made up of carbon, hydrogen, oxygen, nitrogen and phosphorus and which controls the basic functions of the cell. These were first reported by Friedrich Miescher (1871) from the nucleus of pus cell. Altmann called it first time as nucleic acid. Nuclein was renamed nucleic acid by Altman in (1889). They are found in nucleus. They help in transfer of genetic information. Types of nucleic acids : On the basis of nucleotides i.e., sugars, phosphates and nitrogenous bases, nucleic acids are of two types which are further subdivided. These are DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid). (1) DNA (Deoxyribonucleic acids) : Term DNA was given by Zacharis.  (i) Types of DNA : It may be linear or circular in eukaryotes and prokaryotes respectively. Palindromic DNA : The DNA helix bears nucleotide in a serial arrangement but opposite in two strands. \[-T-T-A-A-C-G-T-T-A-A.......\] \[-A-A-T-T-G-C-A-A-T-T......\] Repetitive DNA : This type of arrangement is found near centromere of chromosome and is inert in RNA synthesis. The sequence of nitrogenous bases is repeated several times. Satellite DNA : It may have base pairs up to \[160\,\,bp\]and are repetitive in nature. Microsatellite has \[16\,\,bp\]and minisatellite has \[1160\,\,bp.\] They are used in DNA matching or finger printing (Jefferey). In eukaryotes, DNA is deutrorotatory and sugars have pyranose configuration. (ii) Chargaff’s rule : Quantitatively the ratio of adenine (A) to thymine (T) and guanine (G) to cytosine (C) is equal. i.e., “Purines are always equal to pyrimidine”. (iii) C value : It is the total amount of DNA in a genome or haploid set of chromosomes. (iv) Sense and Antisense strand : Out of two DNA strand one which carries genetic information in its cistrons is called sense strand while the other strand does not carry genetic information, therefore, doesn’t produce mRNA. The non-functional DNA strand is called antisense strand. (v) Heteroduplex DNA : Hybrid DNA formed as a result of recombination is called heteroduplex DNA. It contains mismatched base pair of heterologous base sequence. X-Ray crystallography study of DNA : It was done by Wilkins. It shows that the two polynucleotide chains of DNA show helical configuration. Single stranded DNA (ssDNA) : It is single helixed circular. And isolated from bacteriophage \[\phi \times 174\] by Sinsheimer (1959). It does not follow chargaff’s rule. The replicative form (RF) has plus – minus DNA helix. e.g., parvovirus. Double helical model of DNA: It is also known as Watson and Crick model. (2) RNA or Ribonucleic acid : RNA is second type of nucleic acid which is found in nucleus as well as in cytoplasm i.e., mitochondria, plastids, ribosomes etc. They carry the genetic information in some viruses. They are widely distributed in the cell. Genomic RNA was discovered by Franklin and Conrat (1957).

The arrangement of veins in the lamina of a leaf is called venation. The veins are the hard structures consisting of xylem and pholem. The veins give mechanical strength and shape to the lamina. Angiosperms exhibit two types of venation. (1) Reticulate venation In this type, the lateral veins divide and redivide to form many veinlets. These veinlets are arranged in a net like fashion or reticulum. Reticulate venation is the characteristic feature of dicotyledons. But exceptionally some monocotyledons also show reticulate venation. e.g., Smilax, Alocasia and Dioscorea etc. Reticulate venation is of two types : (i) Unicostate or Pinnate venation : This type of venation is characterized by the presence of a single strong midrib that extends upto the apex of lamina. The midrib produce lateral veins on either side which divide repeatedly. e.g., Ficus and Mangifera. (ii) Multicostate or Palmate venation : Here more than one prominent veins start from the base of the lamina and proceed upwards. The lateral veinlets, arising from main veins, form network. Multicostate venation is of two types : (a) Convergent : When the prominent veins converge towards the apex of lamina. e.g., Zizyphus and Cinnamonum camphora (kapoor), etc. (b) Divergent : When the prominent veins spread out towards the margins. e.g., Papaya, Ricinus, Cucurbita etc. (2) Parallel or Striate venation In this type, veins and veinlets run parallel to each other. Parallel venation is the characteristic feature of monocotyledons. Exceptionally few dicots show parallel venation, e.g., Calophyllum and Eryngium. It is of two types : (i) Unicostate or Pinnate venation : The leaf lamina possesses single prominent vein which gives rise to a large number of lateral veins. All the lateral veins run parallel towards margin. e.g., Banana, Canna, Curcuma etc. (ii) Multicostate or Palmate venation : The leaf lamina possesses several prominent veins which run parallel to each other. It is of two types : (a) Convergent : The prominent veins run parallel to each other and converge at the apex. e.g., Sugarcane, Maize, Wheat, Bambooes and Grasses. (b) Divergent : All the prominent veins of leaf lamina spread out towards the margin. e.g., Fan palm.

The stem develops from the plumule of the germinating seed. Normally it is the aerial part of the plant body. Characteristics of stem (1) Stem is an ascending axis of the plant and develops from the plumule and epicotyl of the embryo. (2) It is generally erect and grows away from the soil towards light. Therefore, it is negatively geotropic and positively phototropic. (3) The growing apex of stem bears a terminal bud for growth in length. (4) In flowering plants, stem is differentiated into nodes and internodes. A node occurs where leaves are attached to the stem. Internode is the portion of stem between the two nodes. (5) The lateral organs of stem (i.e., leaves and branches) are exogenous in origin (from cortical region). (6) The young stem is green and photosynthetic. (7) Hair, if present, are generally multicellular. (8) In mature plants, stem and its branches bear flowers and fruits. Diverse forms of stem (1) Reduced stems : In some plants, the stem is in the form of a reduced small disc which is not differentiated into nodes and internodes. e.g., (a) A reduced green-coloured disc-like stem lies just above the base of fleshy roots of Radish, Carrot and Turnip ; (b) Green-coloured small discoid stem occurs in free-floating Lemna, Spirodela and Wolffia; (c) Highly reduced non-green discoid stem occurs at the base of Onion and Garlic bulbs, etc. (2) Erect stems : Majority of angiosperms possess upright, growing-ascending, vertically-erect stems. They are fixed in the soil with the help of roots. (3) Weak stems : They are thin, soft and delicate which are unable to remains upright without any external support. They are of two types : upright weak stems and prostrate weak stems. (i) Upright weak stem Twiners : The stems are long, slender, flexible and very sensitive. They twin or coil around an upright support on coming in its contact due to a special type of growth movement called nutation. They may coil the support to the right (anticlockwise from the top or sinistrorse) e.g., Convolvulus sp., Ipomoea quamoclit Clitoria ternatea, etc. or to the left (clockwise or dextrorse), e.g., Lablab. Climbers : The stem is weak and unable to coil around a support. They usually climb up the support with the help of some clasping or clinging structure. They are of four types : (a) Tendril climbers : Tendrils are thread like green structure which help in climbing the plants. They may be modified stem (e.g., Vitis), stem branches (e.g., Passiflora) and inflorescence (e.g., Antigonon). (b) Root climbers : Adventitious roots arise from the nodes and penetrate into the upright support so that the climber climbs up, e.g., Betel vine (Piper betel), Tecoma, Ivy, etc. (c) Scramblers or Hook climbers : These weak stemmed plants slowly grow over other bushes and rest there. They attain this position with the help of curved prickles (e.g., Rose), curved hooks on flowering peduncle (e.g., Artabotrys), prickles on stem (e.g., Lantana), spines (e.g., Climbing Asparagus) or spinous stipules more...

The root is usually an underground part of the plant which helps in anchorage of plant in soil and absorption of water and minerals from the soil. The root with its branches is known as the root system. Characteristics of the root (1) The root is the descending portion of the plant axis and is positively geotropic and negatively phototropic. (2) It is non-green or brown in colour. (3) The root does not bear nodes, internodes, leaves and true buds. (4) Usually the root tip is protected by a root cap. (5) The root bears unicellular root hairs. (6) Lateral roots arise from the root which are endogenous in origin (arise from pericycle). Parts of the root (1) Region of root cap : The tip of the root is called calyptra or root cap. It is for protection of root tip against any injury. It is formed from meristem called calyptrogen. Pandanus is the only plant with multiple root caps. In the aquatic plants like Pistia, Lemna and Eicchornia instead of root caps, they have root pockets for buoyancy. The root caps are absent in parasites and mycorrhizal roots. (2) Region of cell formation or meristematic zone : This region of cell division lies protected below the root cap. It comprises of closely arranged, small, thin walled and isodiamatric cells which have dense protoplasm. Vacuoles of the cells are either reduced in size or absent. (3) Region of cell elongation : It lies behind the growing point. Cells of this region lose power of division. The cells elongate due to vacuolation i.e., formation of vacuoles. This region chiefly concerns with absorption of minerals along with some amount of water. (4) Region of cell differentiation or maturation (Root hair zone) : In this region elongated cells are differentiated into permanent tissues depending upon the functions they have to performs. It lies adjacent to the meristematic region some cell of the outermost layer of cells in this region develop root hairs. Most of the water absorption occurs through this region.       Types of root  Tap root : The tap root system develops from radicle of the germinating seed. It is also called the normal root system. The tap root system is present in dicotyledonous plants. Adventitious root : The root system that develops from any part of the plant body other than the radicle is called the adventitious root system. It is mostly seen in monocotyledonous plants. In grasses, fibrous root system is present.

The leaf is a green, flat, thin, expanded lateral appendage of stem which is borne at a node and bears a bud in its axil. It is exogenous in origin and develops from the leaf primordium of shoot apex. The green colour of leaf is due to presence of the photosynthetic pigment – chlorophyll which helps plants to synthesize organic food. The green photosynthetic leaves of a plant are collectively called foliage. Characteristics of leaf (1) The leaf is a lateral dissimilar appendage of the stem. (2) A leaf is always borne at the node of stem. (3) The growth of leaf is limited. (4) The leaves do not possess any apical bud or a regular growing point. Parts of a typical leaf The leaf consists of three parts namely, leaf base (usually provided with a pair of stipules), petiole and leaf blade or lamina. (1) Leaf base (Hypopodium) : Leaf base is the lower most part of the leaf meant for attachment. It acts as a leaf cushion. Some times leaf base shows different variations as follows : (i) Pulvinus leaf base : In members of leguminosae the leaf base is swollen. Such swollen leaf bases are called pulvinus leaf bases as seen in mango leaves. It helps in seismonastic movements (e.g., Mimosa pudica) and nyctinastic movements (e.g., Enterobium, Arachis, Bean).     (ii) Sheathing leaf base : In grasses and many monocots, the leaf base is broad and surrounds the stem as an envelope, such a leafbase is called sheathing leaf base. e.g., Sorghum, Wheat and Palms. In grasses (Sorghum, Wheat etc.) the sheathing leaf base protects the intercalary meristem. (iii) Amplexicaul : Leaf base completely encircles the stem. e.g., Polygonum. (iv) Modified leaf base : The leaf bases in few plants perform accessory functions and show modifications. In Allium cepa (Onion), the leaf bases store food materials and become fleshy. In Platanus and Robenia, the leaf bases protect the axillary buds and grow around them to form cup like structures. (v) Stipule : The stipules are the small lateral appendages present on either side of the leaf base. They protect the young leaf or leaf primordia. Leaves with stipules are called stipulate and those without them are called exstipulate. The stipules are commonly found in dicotyledons. In some grasses (Monocots) an additional outgrowth is present between leaf base and lamina. It is called ligule. The leaves having ligules are called ligulate. Types of stipules : Depending upon the structure and position various kinds of stipules are recognized. Free lateral stipules : A pair of freely arranged stipules present on either side of the leaf base are called free lateral stipules, e.g., Hibiscus and Cotton. Adnate stipules : The two stipules that fuse with the leaf base or petiole on either side are called adnate stipules, e.g., Arachis  and Rose. Inter petiolar stipules : Stipules present in between the petioles of opposite leaves, e.g., Ixora and Hamelia. Axillary stipules : more...

In angiosperms, always the branches are produced by the growth of axillary buds or lateral buds. This type of branching is known as lateral branching. The lateral branching is classified into two kinds racemose and cymose. (1) Racemose branching : In this type of branching, the terminal (or apical) bud of the main stem grows indefinitely and the axillary buds grow out into lateral branches in acropetal succession. This type branching is also called monopodial branching. Due to monopodial branching the shoot system of plant appears conical e.g., Eucalyptus, Polyalthia (Ashoka tree). (2) Cymose branching : In cymose branching the terminal bud is active for a short period and becomes modified into some permanent structures like tendrils, thorns of flowers etc. Due to the terminal bud modification the growth of the main stem is definite. This is also called sympodial branching. Further growth in the plant is carried by one or more axillary buds. Cymose branching may be of three types : (i) Uniparous or Monochasial type : In uniparous type of branching only one lateral branch is produced at each time below the modified terminal bud. Here the successive lateral branches that are formed unite to form a stem. Such a stem is called false axis or sympodium. The uniparous branching is of two kinds, helicoid and scorpoid. (a) Helicoid branching : If the successive lateral branches develop on one side it is called helicoid branching. e.g., Saraca, Canna and Terminalia. (b) Scorpioid branching : If the successive lateral branches develop on either side alternately, it is called scorpioid branching, e.g., Cissus, Gossypium and Carissa.     (ii) Biparous or Dichasial type : When the activity of terminal bud stops, further growth of plant takes place by two lateral branches, e.g., Viscum (Mistletoe), Silene, Stellaria, Mirabilis jalapa (Four O’ clock), Dianthus (Pink), Carissa carandas (Karonda), etc. (iii) Multiparous or Polychasial type : When the activity of terminal bud stops, further growth of plant takes place by a whorl of three or more axillary branches. The axis is said to be multipodial, e.g., Euphorbia tirucalli, Croton, Nerium odoratum (Oleander).

Underground stem The underground stems lack green colour because of their geophillous nature. They can be identified as stems because of the presence of nodes, internodes, scale leaves, buds and branches. Based on the type of growth (transverse/vertical/oblique) and the part that stores food (main stem/ branch/ leaf base), the underground stems are classified into several types : (1) Sucker : This is a sub aerial branch that arises from the main stem. Initially it grows horizontally below the soil surface and later grows obliquely upward. They are shorter and stouter than the runners. e.g., Mentha arvensis (mint vern. Podina) and Chrysanthemum.     (2) Stem tuber : Stem tuber is the tuberous tip of an underground branch. It occurs beneath the soil at any depth. The axillary branches (stolons) that are produced near the soil surface grow into the soil and their tip become swollen due to accumulation of starch and proteins e.g., Solanum tuberosum (potato). In potato, the stem nature is evident by the presence of ‘eyes’ on its brownish corky surface. Each eye is a pit like structure and represents the node. Axillary bud is situated in the pit of the eye. The stem tubers are differentiated from the tuberous roots by the presence of vegetatively propagating eyes. (3) Rhizome : The rhizome is a thickened, underground dorsiventral stem that grows horizontally at particular depth within the soil. The rhizome is brown in colour. It can be distinguished from the modified root by the presence of nodes, internodes, terminal bud, axillary bud and scale leaves. The terminal bud develops aerial shoot that bears inflorescence. Adventitious roots develop on the ventral surface of the rhizome. The rhizomes are perennial and vegetatively propagating structures. It is of following types : (i) Rootstock : They are upright or oblique with their tips reaching the soil surface. e.g., Alocasia indica and Banana. (ii) Straggling : They are horizontal in position and generally branched (Sympodial or Monopodial), e.g., Nelumbo nucifera (Lotus), Zingiber officinale (Ginger), Curcuma domestica (Turmeric), Saccharum etc. (4) Corm : The corm is an underground modification of main stem. It grows vertically at particularly depth in the soil. The corm stores food materials and becomes tuberous. It is non green in colour and conical, cylindrical or flattened in shape. The corm bears scale leaves at each node. In the axils of these scale leaves axillary buds arise which grow into daughter corms. The terminal bud of the corm is large.     It grows into aerial shoot and bears leaves and flowers. Adventitious roots normally develop from the base or all over the body of the corm. With the help of some special adventitious roots called the contractile roots or pull roots, the corm remains constantly at a particular depth. The corm propagates vegetatively by daughter corms. e.g., Amorphophallus, Colocasia and Crocus (Saffron). (5) Bulb : A bulb is a specialized underground stem which more...