NCERT Solutions for Class 11 Biology Chapter 9
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Important Notes on Biomolecules
- Watson and Crick Model: DNA is a right handed, double helix of two polynucleotide chains, having a major and minor groove. The two chains are antiparallel, and held together by hydrogen bonds (two between A and T and three between C and G). The backbone is formed by sugar-phosphatesugar chain.
- The nitrogen bases are projected more or less perpendicular to this, backbone and face inside. The pitch is 34A°. At each step of ascent, the strand turns 36°. The rise per base pair is 3.4°A, so one full turn involves ten base pairs.
- Water insoluble, containing C, H, O.
- Fats on hydrolysis yield fatty acids.
- Fatty acid has a carboxyl group attached to an R group (contains 1 to 19 carbons).
- Fatty Acids: Saturated: With single bonds in carbon chain, e.g., Palmitic acid, butyric acid.
- Unsaturated: With one or more double bonds, e.g., oleic acid, linoleic acid.
- Polysaccharides: These are long chain of polymers of monosaccharides.
- Starch: Store house of energy in plant tissues. Forms helical secondary structures, made of only glucose monomers.
- Cellulose: Homopolymer of glucose. It does not certain complex helices. Cotton fible is cellulose.
- Glycogen: Is a branched homopolymer, found as storage polysaccharide in animals.
- Inulin: Is a polymer of fructose.
- Chitin: Chemically modified sugar (amino-sugars) N-acetyl galactosamine form exoskeleton of arthropods; heterpolymer.
- Peptide bond-formed between the carboxyl (-COOH) group of one amino acid, and the amino (- NH2) group of the next amino with the elimination of water moiety, (dehydration).
- Glycosidic bond-bond formed between two carbon atoms of two adjacent monosaccharides., by dehydration.
- Phosphodiester bond-bond formed in nucleic acids where in a phosphate moiety links the 3-carbon of one sugar of one nucleotide to the 5-carbon of the sugar of the succeeding nucleotide. (The bond between phosphate group and hydroxyl group of sugar).