Ecosystems Interactions between communities and their physical environments form systems known as ecosystems. One of the major phenomena underlying an ecosystem is the flow of energy. Because photosynthesizing organisms trap the energy in an ecosystem, they are producers. Because certain organisms in the community meet their energy needs by feeding on these producers, they are consumers. Producers are usually autotrophs, while consumers are usually heterotrophs. Primary consumers feed directly on plants, while secondary consumers (carnivores) feed on the animals that eat the plants. The energy flow forms a one-way pattern; the energy is used for metabolic reactions and the remainder is given off as heat. The transfer of food energy from producers to consumers is the food chain. Many food chains intertwine in a complex manner to form a food web.
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