Energy flow through biological systems

The Sun is the principal source of energy entering biological systems. Producers, such as plants, capture some of its light energy and convert it into chemical energy stored in organic substances. For example, plants use light energy to make sugars during photosynthesis.

When one organism feeds on another, some of the chemical energy stored in organic substances passes to the feeding organism. In this way, energy moves from producers through other organisms as they feed.

Organisms use energy for their life processes. As they use it, energy is eventually transferred to the environment, chiefly as heat. Energy therefore flows into biological systems as light, passes through organisms as chemical energy, and is transferred out to the environment.