What happens to the amount of energy at successive trophic levels?

The correct answer is Option (3) → It decreases.

Energy enters an ecosystem when producers capture sunlight. It then passes from producers to herbivores to carnivores. At every step, much of the energy is used by the organism for its own life processes and is lost as heat. Only a small part is passed on to the next level. So the amount of energy becomes smaller at each higher trophic level.

Option (1) It remains constant. — Incorrect. Energy cannot stay the same, because some of it is lost as heat at every transfer.

Option (2) It increases. — Incorrect. No trophic level can pass on more energy than it receives. Energy flow is one-way and shrinking.

Option (3) It decreases. — Correct. Because of the heat loss at each step, the amount of energy decreases at successive trophic levels.

Option (4) It varies depending on the ecosystem. — Incorrect. The decrease happens in every ecosystem. This is why the pyramid of energy is always upright.

NCERT Extract:
Energy Flow – “… All organisms are dependent for their food on producers, either directly or indirectly. So you find unidirectional flow of energy from the sun to producers and then to consumers. … The important point to note is that the amount of energy decreases at successive trophic levels.”

Figure 12.3 Energy flow through different trophic levels