Which of the following is a correct statements?

Option A is correct. Energy enters the biosphere as sunlight, is captured by producers through photosynthesis, passes to herbivores and then carnivores, and finally leaves the system as heat. Under the second law of thermodynamics that heat cannot be reconverted into usable energy for the ecosystem, so energy flow is one-way. It is never recycled.

• B is wrong: Cyclic movement applies to matter, such as carbon, nitrogen and phosphorus in biogeochemical cycles. Energy does not cycle.
• C is wrong: Lindeman's 10% law shows that about 90% of energy is lost at each transfer. The relative loss stays roughly constant across trophic levels. It does not decrease.
• D is wrong: The narrowing of the pyramid reflects less energy being available at higher levels. It does not mean higher-level species are inherently less efficient at using the energy they receive.

The core concept is the difference between energy flow and nutrient cycling, which underpins food chains, ecological pyramids and carrying capacity. In Mains, it connects to biomagnification of persistent pollutants and to why diets high in animal protein carry larger ecological footprints.

Trap: Aspirants see the word 'cycle' in the nutrient context and pick B. Remember that matter cycles and energy flows.