Energy flows through an ecosystem in a linear, one-way direction. In all ecosystems, energy enters the system as sunlight (radiant energy). Producers (photosynthetic organisms) trap and use about 0.02% of the sun's energy in photosynthesis.

In the food chain, herbivores eat producers, carnivores eat herbivores, and decomposers break down the remains. At each step, organisms use energy to do biological work and lose most of their energy to the environment.

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