Green plants use a pigment called chlorophyll to convert energy from sunlight into chemical energy. The plant takes the light energy and combines it with six molecules of carbon dioxide and six molecules of water to form one molecule of glucose and six molecules of oxygen. Oxygen is the by-product of photosynthesis. The plant can also store the energy for future use. Basically, this process makes food out of energy.

Respiration is the release of the energy derived from the food created by photosynthesis. It occurs all the time in all living cells. There are different kinds of respiration:

Sugars produced by photosynthesis are used directly in respiration. Usually, photosynthesis will produce more glucose than is needed by the plant. The excess sugars are stored and transformed into starch, cellulose, lipids (fats) and other carbohydrates, proteins and sucrose.