Plant cells store food primarily as starch, a white, granular organic chemical. Plants produce starch in their green leaves from excess glucose created during photosynthesis. When needed, plants can break down starch into glucose units for energy.

On the other hand, animal cells store food as glycogen, a polysaccharide of glucose. The hormone insulin converts excess glucose in the blood into glycogen, which is then stored in the muscles and liver. When the body needs extra energy during exercise, glycogen is broken down into glucose.