An ecosystem is an interactive unit that consists of all interacting organisms in a particular area, along with their abiotic or physical surroundings. Usually, ecosystems are divided into trophic levels namely; producers, primary consumers, secondary consumers and tertiary consumers. Energy is not recycled in an ecosystem, but rather it flows in an ecosystem. In an ecosystem, energy flow can be described as energy transfer from one organism to another. According to McShaffrey (2006), each organism interacts with the ecosystem in 2 ways; obtaining food energy from the ecosystem and contributing energy to the ecosystem. Energy flow starts at the trophic level of the producers whereby plants capture light energy from the sun. Through photosynthesis, producers such as grass convert the light energy to chemical bond energy e.g. carbohydrates.
When primary consumers or herbivores such as grasshoppers eat this grass, they obtain this chemical energy as organic compounds of food. Consequently, secondary consumers such as frogs feed on primary consumers and obtain the chemical energy. Top carnivores such as hawks or eagles then obtain this energy by feeding on the secondary consumers. Finally, decomposers use organic molecules found in dead organisms their energy source. Therefore, energy flow through an ecosystem is mainly through feeding relationships and can be clearly illustrated in a food chain. Only a fraction of energy that goes through a particular trophic level is eventually stored organisms’ bodies at the next trophic level. Much of the energy is expended on life processes such as movement, respiration, growth and reproduction, while the rest is dissipated to the environment as heat energy (McShaffrey, 2006). Therefore, energy enters the ecosystem as sunlight or light energy, is converted and used within the ecosystem as chemical energy (as food such e.g. carbohydrates) and is lost from the ecosystem in form of heat.
McShaffrey, D. (2006, February 3) Environmental Biology-Ecosystems. Retrieved from http://www.marietta.edu/~biol/102/ecosystem.html