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 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 more...

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 more...

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 more...

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 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 more...

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) : 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 more...

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 more...