CBSE Class 10 Science 2019 · Paper 31/5/1 · Question 9(a)

A food chain is a series of organisms in which each feeds on the one before it, so that food and energy pass from one trophic level to the next; for example, grass $\to$ deer $\to$ lion. The flow of energy is unidirectional because (any two): the energy captured by the autotrophs does not revert to the solar input; the energy passed to the herbivores does not come back to the autotrophs; only about $10\%$ of the energy at one level is passed on and the rest is lost as heat, so energy that has moved on is no longer available to the previous level.