Name important defence mechanisms in plants against herbivory.
Plants have evolved two main types of defence mechanisms against herbivory:
Morphological Defences: These are physical structures that deter herbivores. The most common morphological defence is thorns, as seen in plants like Acacia and Cactus. These structures physically prevent animals from feeding on the plant.
Chemical Defences: Many plants produce and store various chemicals that act as potent weapons against herbivores. These chemicals can make the herbivore sick, inhibit feeding or digestion, disrupt reproduction, or even kill the herbivore. For example, the weed Calotropis produces highly poisonous cardiac glycosides, which is why cattle and goats never browse on this plant.
Explanation
The question asks for important defence mechanisms in plants against herbivory. According to the NCERT textbook context, plants have evolved two primary categories of defences since they cannot run away from predators (herbivores): (1) Morphological defences - primarily thorns as physical barriers, and (2) Chemical defences - toxic or deterrent chemicals stored in plant tissues. The textbook specifically mentions Acacia and Cactus as examples of thorn-bearing plants and Calotropis as an example of a chemically defended plant with cardiac glycosides. This 2-mark answer requires naming both types with examples for full marks.
Solution Steps
Step 1: Identify the two main categories of defence mechanisms from the context - morphological and chemical defences.
Step 2: Provide examples for each type - thorns (Acacia, Cactus) for morphological and cardiac glycosides (Calotropis) for chemical defences.