The energy available to living systems comes from the sun. Plants that contain chlorophyll capture light energy and store it in sugars using a process called photosynthesis .
Autotrophs are organisms that can make their own food.
Once the plants have store this energy, it is available for use by them, or other organisms in an ecosystem. The release of energy from stored sugars is called respiration . It is important to remember here that plants use respiration to grow and conduct other activities of life just as much as animals do. Animals cannot make their own food, so we call them heterotrophs. Animals must eat plants, or other animals to use the energy stored.