Consider the following statements about predation and defences against it:
A. Nicotine, caffeine, quinine, strychnine and opium are produced by plants as defences against grazers and browsers.
B. Thorns (Acacia, Cactus) are the most common chemical means of defence in plants.
C. Some species of insects and frogs are cryptically-coloured (camouflaged) to avoid being detected easily by the predator.
D. If a predator is too efficient and overexploits its prey, the prey might become extinct and, following it, the predator will also become extinct.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A, C and D only
A. Nicotine, caffeine, quinine, strychnine and opium are produced by plants as defences against grazers and browsers. — True. Many chemicals we extract from plants on a commercial scale are made by the plants as chemical defences against herbivores.
B. Thorns (Acacia, Cactus) are the most common chemical means of defence in plants. — False. Thorns are a part of the plant body, so they are the most common morphological means of defence. Chemical defence uses substances such as the cardiac glycosides of Calotropis.
C. Some species of insects and frogs are cryptically-coloured (camouflaged) to avoid being detected easily by the predator. — True. Camouflage is one of the defences of prey; the prey blends with its surroundings.
D. If a predator is too efficient and overexploits its prey, the prey might become extinct and, following it, the predator will also become extinct. — True. The predator would be left without food. This is why predators in nature are ‘prudent’.
NCERT Extract:
Population Interactions – “… If a predator is too efficient and overexploits its prey, then the prey might become extinct and following it, the predator will also become extinct for lack of food. This is the reason why predators in nature are ‘prudent’. Prey species have evolved various defenses to lessen the impact of predation. Some species of insects and frogs are cryptically-coloured (camouflaged) to avoid being detected easily by the predator.”
Population Interactions – “… Thorns (Acacia, Cactus) are the most common morphological means of defence. Many plants produce and store chemicals that make the herbivore sick when they are eaten, inhibit feeding or digestion, disrupt its reproduction or even kill it. … A wide variety of chemical substances that we extract from plants on a commercial scale (nicotine, caffeine, quinine, strychnine, opium, etc.,) are produced by them actually as defences against grazers and browsers.”