Solution: A category of animals that feeds only on plants is known as herbivores and this state or condition is called herbivory. Plants have evolved mechanisms both chemical and morphological, to protect themselves against the herbivores. The defense mechanisms of few plants are discussed below.

Chemical defense mechanisms:

• Caffeine, nicotine, opium, and quinine are some chemical substances that are produced in some plants which is a response and defense mechanism against herbivory.
• All of the parts of Calotropis weeds consist of lethal cardiac glycosides (cause cardiac problems) that proved to be fatal if consumed by herbivores.

Morphological defense mechanisms:

• Opuntia or cactus leaves are altered into thorns or sharp spines to prevent herbivores from feeding on them. this is a morphological change to develop a defense mechanism.
• Margins of leaves in some plants became spiny, having sharp edges, causing difficulties for herbivores to feed on them.
• Sharp thorns with leaves are found in Acacia to prevent herbivores from feeding on them