Give an account of energy flow in the ecosystem.

Hint: The Energy flow in an ecosystem follows the Lindeman's Law.

Complete answer:
The flow of energy in an ecosystem is unidirectional, starting from the producers (1st Trophic Level) and ending at decomposers (6th Trophic Level).
The energy flow in an ecosystem that can be explained using the 1st and 2nd laws of thermodynamics.
- First Law of Thermodynamics: It states that matter or energy can neither be created nor destroyed, but it can be converted from one form to another.
- Second Law of Thermodynamics: During the transfer of energy from one trophic level to another trophic level some energy is lost as heat or entropy.

Sun is the only and primary source of energy for almost all ecosystems. The solar energy incident on the Earth's surface can not be completely converted to energy by plants or producers, less than 50% of incident solar radiation is photosynthetically active radiation or PAR. And plants can only trap 1-5% of the incident radiation or 2-10% of the photosynthetically active radiation for photosynthesis. Respiratory energy losses also occur which is about 20%, so the net primary productivity is around 0.8 - 4% of incident solar radiation or 1.6 - 8% of PAR.

Lindeman’s Law- It is also known as 10% law, which states that only 10% of the energy in one trophic level can be transferred to the next trophic level.

Ecological Efficiency is the ratio between energy assimilated over the energy available between two successive trophic levels. It is of the following types:
- Photosynthetic Efficiency
- Net Production Efficiency
- Assimilation Efficiency
- Ecological Efficiency

Note: Solar energy may be the primary source of energy for a majority of organisms except for the deep-sea hydrothermal ecosystem. These organisms most probably obtain nutrition from chemosynthesis.
It is to be noted that only a minute amount of energy is transferred from one trophic level to another (10% Law).