Question

(a) With the help of a flow diagram, describe how energy from the sun flows through various trophic levels.
(b) Explain why, the flow of energy in the ecosystem is said to be unidirectional.

Answer 1

(a) Energy from the sun flows through various trophic levels in the following steps.
1) Green plants trap solar energy with the help of their green pigment, chlorophyll, and convert it into chemical energy. They store this energy in the form of carbohydrates. On an average, about one per cent of the sun's energy falling on the leaves of green plants is used by the plants in the process of photosynthesis and stored as the chemical energy of food.
2) When plants are eaten by herbivores, the chemical energy stored in the plants is transferred to them.
3) The herbivores are then consumed by carnivores, and the chemical energy stored in the flesh of the herbivores is transferred to the carnivores.
4) Some of the energy from producers and consumers is also utilised for the life processes of micro-organisms called decomposers. Decomposers, in turn, release the unutilised energy into the environment as heat. The energy that is not utilised by producers, consumers and decomposers is lost in the environment as heat. This heat is called community heat.

(b) Energy enters plants from the sun during food production through photosynthesis. This energy is then passed on from one organism to another in a food chain. The energy given out by organisms as heat is lost in the environment and does not return to be used by plants again. This makes the flow of energy in an ecosystem unidirectional. Thus, the flow of energy in an ecosystem is said to be unidirectional because the energy lost as heat from the organisms in a food chain cannot be reused by plants in photosynthesis.