The amount of energy during transfer from one tropic level to another in an ecosystem

Energy moves through a food chain in one direction, and a large share is lost at every transfer. So the energy passed from one trophic level to the next decreases. This is the core of Lindeman's 10 per cent law: only about 10 per cent of the energy assimilated at one level becomes biomass available to the next. The rest is lost mainly as heat through respiration, along with unassimilated material in faeces and energy spent on movement and metabolism.

• A) increases: Energy is not created in a food chain. Producers fix solar energy, and the chain passes on only a fraction of it upward.
• C) remains constant: This would contradict the second law of thermodynamics. Every transfer is inefficient, so there is always a loss.
• D) may increase or decrease: This is a hedge. Energy flow is unidirectional and the loss is consistent, so the answer is not variable.

Mains connection: because the energy pyramid is always upright, food chains are short, top predators are few, and efficient primary production matters for food security.

Trap: candidates mix up energy with biomass or numbers of organisms, where pyramids can appear inverted in some aquatic systems. Energy pyramids are never inverted.