Food chains describe the flow of energy through an ecosystem. Primary producers pump energy into an ecosystem from an environmental source, and this energy is then passed from one organism to the next.

The energy source for many ecosystems is the Sun. However, some ecosystems, such as those located near hydrothermal vents on the sea floor, rely on energy from inorganic compounds.

Much of the energy put into each level of the food chain is lost. Some of the energy is used in carrying out life processes while some of the food consumed is undigested and passes as waste.

Primary producers convert energy from the environment into a usable chemical form. Plants, algae, and some bacteria use photosynthesis to harness the energy from sunlight to drive life processes.

Primary consumers obtain their needed energy by consuming the energy stored in the cells and tissues of primary producers. Examples of primary consumers include grazing animals such as zebras, buffalo, and horses.

Primary consumers in turn become prey for secondary consumers. Secondary consumers include predators such as snakes, lions, and wolves.

Decomposers such as fungi break down organic material distributed by other organisms into the environment. This material may come from dead organisms or waste excreted after digestion.