Organisms and Populations — BIOLOGY STD 12 Science — Question

Herbivores are the predators for plants. Nearly 25% of all insects are phytophagous as they feed on plant sap and other parts of plants. Plants have severe problem to protect themselves from predators because they cannot run away like animals. That is why plants have developed several morphological and chemical means of defence against herbivores. The general example of morphological defence is the presence of thorns or spines in Acacia and cactus. The plum bush has thorns. Many plants produce and store chemicals which render herbivores sick, inhibit their digestion or kill them when eaten by herbivores. Calotropis weed growing in abandoned fields produces more foxic glycosider that is why not eaten by any animal. A wide variety of chemical substances like nicotine, caffeine, quinine, strychine, opium etc. are extracted. In fact, these chemicals are the defence means methods against grazers and browsers.