All living things derive energy from the food they consume. As food passes through the system, some of it is digested, in a physical process that releases energy.
4:47 · Life Science
A food chain is composed of a group of organisms in which each member of the group feeds on the one below it (and is eaten by the one above it). In this way, food energy is transferred. However, only about 10 percent of the food energy is retained by the level above; 90 percent is not retained.