Plants make carbohydrates in the form of sugar during the process of photosynthesis. The green leaves of plants absorb sunlight, and they use this energy to combine water with carbon dioxide. This process yields two byproducts — oxygen and glucose (sugar). Photosynthesis would be impossible without chlorophyll, the green pigment that transforms light energy from the sun into chemical energy.
Photosynthesis occurs in the mesophyll cells, which contain stacks of chloroplasts, which are chlorophyll-bearing structures. An input of six carbon dioxide and six water molecules are necessary for the chloroplasts to convert sunlight into one molecule of carbohydrates that the plant can store as chemical energy. The most common reaction creates a glucose molecule, but the molecule can also be further transformed into starch, cellulose or lignin. This reaction also releases six oxygen molecules, which is essential to maintaining a balance in the Earth’s ecosystems. Humans and other mammals use this oxygen byproduct for respiration.
When plants create and store carbohydrates, they are able to survive for brief periods when one of the ingredients necessary for photosynthesis is lacking. But humans have also found great benefits in the chemical energy plants possess. Firewood, for example, is rich in stored energy. Likewise, humans and animals receive nourishment from eating the stored energy in fruits and vegetables.