Previous Year Question
Which of the following is a correct statement?
Energy flow in the biospheric ecosystem is unidirectional.
Energy flow in the biospheric ecosystem is cyclic.
Relative loss of energy in natural ecosystem decreases with increasing trophic levels.
Species at progressively higher trophic levels appear to be less efficient in using available energy.
Correct Answer: A
Detailed Solution
The principal source of energy in an ecosystem is the Sun. Producers, mainly green plants, convert Solar Energy into chemical energy through Photosynthesis.
Energy then generally flows in the direction—
Sun → Producers → Herbivores → Carnivores → Decomposers
As energy passes from one trophic level to the next, a large part is dissipated into the environment through respiration, metabolic activities and heat. Therefore, this energy does not return to Producers in the same form to form a cycle.
This is why matter/nutrients are recycled, whereas energy flows in one direction.
According to the general ecological 10% Law, only about 10% of the energy available at one trophic level is transferred to the next. For example, if Producers contain 10,000 units of energy, about 1,000 may reach Primary Consumers, about 100 may reach Secondary Consumers and about 10 may reach the next level. This is a general ecological approximation and need not be exactly 10% in every ecosystem.