Herbivores get energy by eating plants. Plants get energy from sunlight. Why does most of the energy captured by plants never become available to herbivores?

The majority of the energy captivated by the plants never become accessible to herbivores because of the 10 percent rule, that is, for each trophic level, only approximately 10% of the energy moves from one level to the next level.  

•An animal, which primarily consume plants and its products is termed herbivore.  

•The herbivores occupy the second level and consume producers, that is, the plants, thus, they are termed as the primary consumers.  

•Approximately, 10% of the energy is passed from one level to the next, for each trophic level. This is known as the 10% rule.  

•Due to this rule, the herbivores only get about 10% of the energy stored by the plants they consume.

Thus, due to 10% energy rule, the majority of the energy captured by the plants never become available to herbivores.

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Because they lose most of the energy as heat when they perform metabolic activities

Explanation:

Cells of all living organisms require energy in form of ATP to perform their cellular functions. In an ecosystem, organisms obtain this energy by feeding on one another. However, these energy transfer starts from organisms capable of using sunlight called PRODUCERS e.g plants.

Herbivores, which are PRIMARY CONSUMERS get their energy by feeding on these plants. However, according to the PYRAMID OF ENERGY, which represents the flow of energy in an ecosystem, only a few portion of the energy (about 10%) derived by plants from the sun gets transferred to herbivores. This is because most of the energy (about 90%) is lost as heat when the plants undergo metabolic activities.

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