When organisms in an ecosystem eat food, they obtain energy. Organisms use some of this energy to perform life processes such as growing, moving, and reproducing. Only some of the energy organisms obtain will be available to the next organisms in the food web. A diagram called an energy pyramid shows the amount of energy that moves from one trophic level to the next in a food web. The most energy available is at the producer level. As you move up the levels in the energy pyramid, less energy is available than at the level below.

On average, about 10 percent of the energy available within one trophic level is transferred to the next level. The other 90 percent is given off as heat during life processes. Look at the pyramid below. It shows a pyramid of energy. Energy is expressed in Kcal or kilocalories.