Energy flow is a fundamental process and happens in all ecosystems. Energy is defined as the capacity to do work. The movement of energy through a series of organisms in an ecosystem is what is called energy flow in an ecosystem.
All organisms require energy to do anything. This energy is obtained from the chemical energy of food that they consume. This chemical energy is obtained, in turn, from the conversion of the radiant energy of the sun.
Organisms are either producers or consumers in terms of the energy flow through the ecosystem. Plants are producers. They take energy from sunlight and convert it into organic material through the process of photosynthesis. This takes place at the first trophic level and plants are primary producers.
At the second trophic level are herbivores who use plants as food. This gives them energy. Most of this energy is used up in performing metabolic functions such as breathing, food digestion, the growth of tissues, maintaining body temperature and blood circulation.
At the next trophic level come carnivores. Carnivores feed on the herbivores and derive energy for their growth and sustenance. Large predators are present in subsequent trophic levels and they derive their energy by consuming smaller carnivores. Some organisms like human beings consume both plants (producers) and animals for their food.
Organisms that can fix radiant energy utilizing inorganic substances to produce organic molecules are called autotrophs/producers. Plants are examples of autotrophs.
Heterotrophs are organisms that cannot obtain energy from abiotic sources and rely on energy-rich organic molecules synthesised by autotrophs.
Consumers are those that obtain energy from living organisms and decomposers are those that obtain energy from dead organisms.
At each trophic level (also called feeding level), heat energy is released thereby reducing the amount of energy passing onto each level. That means energy is degraded. The flow of energy is also only unidirectional.
At the last level, all organisms die and become detritus or food for decomposers. Here, the last remnants of energy are extracted and released as heat energy, while the inorganic nutrients are returned to the soil or water only to be taken up again by primary producers. The energy is lost or released while the inorganic nutrients are recycled.
The ultimate source of energy is the sun. Ultimately, all energy in ecosystems will get lost as heat.
A food chain may be defined as the transfer of energy and nutrients through a succession of organisms through repeated process of eating and being eaten.
Only green plants are able to trap solar energy and convert it into chemical energy. This chemical energy is locked up inside chemical organic compounds like fats, carbohydrates, proteins, etc. When herbivores eat plants, they get some of the energy in the plants. Animals feeding on other animals lead to the energy being flown through these organisms. In this manner, one form of life supports another. Finally, the last of the energy is released in the form of heat by decomposers.
In nature, there are several food chains. These food chains are not independent of each other but interlinked to one another. An organism on one food chain can be eaten by several other creatures. Also, bigger carnivores need not always consume a carnivore one step lesser in the food chain. They may directly consume herbivores. This leads to complex food webs and not linear chains.
Energy flow in ecosystems is an important topic in UPSC environment and ecology sections. This is a basic concept in the subject and one that has to be understood thoroughly. It will help in developing an understanding of the various biogeochemical cycles in nature. It is a part of General Studies III in the UPSC syllabus.
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