Biology · Organisms and Populations · NEET
Calotropis produces highly poisonous cardiac glycosides. This is why cattle and goats never browse on it. NEET has asked this exact fact directly (2023), so remember the pair: Calotropis = cardiac glycosides. Do not confuse it with ricin (castor), quinine, or strychnine, which come from other plants.
Camouflage is cryptic colouration. The prey's body colour blends with its surroundings so the predator cannot detect it easily. NCERT gives examples of some insects and frogs that are cryptically-coloured to avoid being seen. Camouflage does not make the prey poisonous; it only hides it.
The Monarch butterfly is highly distasteful to its predator (a bird) because of a special chemical in its body. It does not make this chemical itself as an adult. It acquires the chemical during its caterpillar stage by feeding on a poisonous weed. So it is a case of chemical (not morphological) defence in animals.
For plants, herbivores are the predators, because plants cannot run away. Plants use two kinds of defence: morphological (thorns in Acacia and Cactus) and chemical (poisonous or feeding-inhibiting substances). Examples of plant defence chemicals in NCERT are nicotine, caffeine, quinine, strychnine, opium, and the cardiac glycosides of Calotropis.
Yes. NCERT clearly states that a wide variety of chemicals we extract commercially (nicotine, caffeine, quinine, strychnine, opium, etc.) are actually produced by plants as defences against grazers and browsers. NEET may ask which chemical belongs to which plant, so learn Calotropis = cardiac glycosides as the anchor example.
For chemical defence against herbivores, Calotropis has:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Camouflage (cryptic colouration) is a way to avoid detection by matching the surroundings. It is different from morphological defences like thorns and from chemical defences like poisons. In animals, the main defences NCERT lists are camouflage and being poisonous/distasteful.
Thorns (Acacia, Cactus) as a morphological defence, and chemical defences such as cardiac glycosides in Calotropis and other chemicals like nicotine, quinine and strychnine that make herbivores sick or inhibit feeding.
Plants are fixed in one place, so unlike animals they cannot run away from herbivores. This is why plants have evolved so many morphological (thorns) and chemical defences instead.
Calotropis = cardiac glycosides. This exact fact was asked in NEET 2023, so it is the highest-yield point on this topic.
