BIOLOGY STUDY MATERIALS

biologicalinform.blogspot.com WATSON AND CRICKS MODEL OF DNA The double stranded helical structure of DNA was proposed for the first time by James Watson and Francis Crick in 1953. In Eukaryotic, DNA molecule is present in each chromosomes if nucleus. The two strands of DNA molecule are spirally twisted around each other as well as a central axis to form tight handed double helix. The coiling of two strand is plectonemic i.e. the two strands can’t be easily separated from each other. The backbone of strand is formed by alternately arranged Deoxyribose sugar and phosphate molecular which are joined together by Phosphodiester bonds . Each strand is long polypeptide chain composed of many basic units or monomers known as Deoxyribonucleotides, hence called polymer compounds. Each transverse step is made up of nitrogen bases which are purines and pyrimidines. Nitrogen bade is attached horizontally at carbon number one of Deoxyribose sugars. The nitrogen bases of two DN

LICHENS The lichens word was first used by Theophrastus in 300 B.C. The Lichens are the organism which form with two different partners fungi and algae. fungi and algae are in symbiotic relation which help to one another.  The lichens are distributed in wide variety of habitats. They grow on tree trunks, decaying logs, and on soil too. They are found in extreme  climatic conditions such as on dry exposed rocks and also at snow covered Arctic and Antarctic poles. They are sensitive to air pollution and generally do not grow near th cities. Their thallus are greenish or bluish green in colour, but some time yellow, orange, brown and block colour found as have additional pigments in lichens. Alexopoulos and Mims classify the lichens on the basis of fungal components like Ascolichens, Basidiolichens and Deuterolichens. On the basis of external form the lichens are of types- Leprose Lichens- The simplest type of  lichens. The thallus in which fungal hyphae envelops either si