An ecosystem is a functional unit of nature in which living organisms interact among themselves and with the physical environment through the exchange of energy and matter. In environmental geography, the ecosystem is studied to understand how natural systems operate, maintain balance, and support life on Earth. The functions of an ecosystem explain the processes through which the biotic and abiotic components are linked and sustained over space and time. One of the primary functions of an ecosystem is energy flow. Energy enters the ecosystem mainly from the sun and is captured by green plants through the process of photosynthesis. This energy is then transferred from producers to consumers and finally to decomposers through food chains and food webs. At each trophic level, a part of energy is lost as heat, following the laws of thermodynamics, which explains why energy flow is unidirectional and non-cyclic. Sun ↓ Producers (Plants) ↓