For example, in photosynthesis plants take in radiant energy from sunlight. This solar energy is stored in complex chemical compounds such as starches and sugars. The stored energy is released when these compounds break down into simpler compounds.
When you eat plant or animal tissue, your digestive system adds chemicals called enzymes that help break down the food. Digestion converts stored energy in food to other forms of energy that your body can use, such as mechanical energy to walk across the room.