Energy 1s the capacity to do work. Without energy no work can be done. Since all living organisms Work, they constantly require energy.
According to the first law of thermodynamics, energy cannot be created and cannot be destroyed. It can only be transformed from one form to another. Therefore, the whole energy of this universe is constant. Whenever a work is done, a transformation or transfer or both) of energy takes place. The best example of energy transformation in nature is that of light energy (from sun) into chemical energy (food) by green plants (photosynthesis).
Main source of energy for an ecosystem is the solar energy. The amount of solar energy reaching the earth’s surface is 2 Cals/cm/min, it is almost constant and is called as ‘solar constant or solar flux’. Of this energy, 95 to 99 % energy is lost due to reflection. Plants and algae utilize about 0.02 % of the solar energy, reaching the earth. They convert this energy into chemical energy by photosynthesis.
6CO2 + 12 H2O Green plant C6H1206 + 602 + 6 H2O
The flow energy in an ecosystem means its flow from one trophic next successive level or trophic level.
Energy flow is always unidirectional from producer to consumer level it is never reversed. Hence energy in an ecosystem can be used once only (however minerals and other inorganic components can be recycled for many times in the same ecosystem).
Table of Contents
Each food chain consists of many steps or energy levels like producer level, Producer consumer level, secondary consumer level and tertiary consumer levels. Each such step or energy level’ is called trophic level.
10% energy transfer law:
A large amount of energy is lost at each trophic level during its flow. It is estimated that 80 to 90 % of the energy is lost at each trophic level.
Only about 10 o energy is transferred from one level to the next level. This is called 10% energy law proposed by Lindeman.