CBSE Class 9 Biology The Fundamental Unit of Life Notes Set 06

Protoplasm

Every cell has a plasma membrane and protoplasm. After removing the nucleus, organelles and inclusions, the ground substance is called cytoplasm (hyaloplasm). The term protoplasm was introduced by Purkinje.
Physical properties: it is a polyphasic colloidal system; its specific gravity is slightly above that of water; it responds to stimuli (irritability); it shows streaming and amoeboid movement; the pH of cytoplasm is slightly acidic (about 6.8) while that of nucleoplasm is 7.6 to 7.8.

Chemical Composition

1. Organic and inorganic compounds occur in the cell in a ratio of about 9 : 1.
2. Inorganic compounds: water (55 to 60 percent of living material), minerals and salts (1 to 3 percent) and dissolved gases. Water is the universal solvent, a medium for reactions and heat transfer, and a lubricant.
3. Organic compounds: carbohydrates, lipids, amino acids and proteins, nucleic acids and vitamins.

Carbohydrates

1. General formula Cn(H₂O)n; they are polyhydroxy aldehydes or ketones and give about 4 kcal of energy per gram.
2. Monosaccharides cannot be hydrolysed: glucose and fructose (hexoses, C₆H₁₂O₆), galactose, ribose and deoxyribose (pentoses).
3. Disaccharides: maltose = glucose + glucose; lactose = glucose + galactose; sucrose = glucose + fructose.
4. Polysaccharides: starch (storage in plants, blue colour with iodine), glycogen (storage in animals, in liver and muscles), cellulose (cell walls of plants, cannot be digested by humans).

Lipids, Proteins and Vitamins

1. Lipids (fats, oils, waxes) are insoluble in water and give the highest energy per gram. Unsaturated fatty acids have at least one double bond.
2. Proteins are polymers of amino acids joined by peptide bonds. Essential amino acids must come from food; non-essential ones are made in the body. All enzymes are proteins and collagen is the most abundant protein in the body.
3. Vitamin C comes from citrus fruits; vitamin A is rich in cod liver oil, carrots and papaya.

Nucleic Acids

1. DNA and RNA are polymers of nucleotides. A nucleotide has a nitrogenous base, a pentose sugar and a phosphate group.
2. DNA has deoxyribose and the bases A, G, C and T; RNA has ribose and the bases A, G, C and U.
3. Watson and Crick proposed the double helix model of DNA (1953). DNA replicates in the S phase of the cell cycle using DNA polymerase; ligase joins DNA fragments.
4. Transcription makes RNA from a DNA template; translation makes a protein from m-RNA.