Ecosystem — BIOLOGY STD 12 Science — Question

The entry, transfer, transformation and distribution of energy in the ecosystem occurs in accordance with the two basic laws of thermodynamics. The ability to do work is called energy. Every living organism requires energy for its biological activities. Sun is the only source of energy for all the ecosystems of earth. (Diagram 12.2). Only 1% of the total solar energy reaching the earth is converted into food energy or chemical energy through photosynthesis. In forest trees the efficiency can be upto 5%. The remaining energy is dissipated as heat. About 90% of the total photosynthesis on earth in performed by aquatic plants, especially sea diatom algae and remaining part is done by terrestrial plants. Among these trees carry out maximum photosynthesis in forest followed by cultivated plants and grasses.
Organisms cannot utilize more than 10% of the energy obtained in anabolic activities and remaining 90% of energy is dissipated as heat in activities like respiration ie only 10% energy is stored at each trophic level of food chain during tranfer of energy. This is called the Rule of ecological tenth.
If 100 calorie solar energy is available at any place, plants (primary producers) obtain 10 calorie, herbivores (primary consumers) feeding on these plants obtain 1 calorie, carnivores (secondary consumers) feeding on herbivores store only 0.1 calorie and at decomposers it will be minimum Thus energy concept involves transfer and transformation of energy from one trophic level to another.