Plants make oxygen through a process called photosynthesis. Oxygen is produced as a waste product for the plant as the plant makes its own food. Photosynthesis literally means “making things with light.” Photosynthesis requires six carbon dioxide molecules and six water molecules to produce glucose, a sugar that serves as food for the plant. As a result of photosynthesis, six oxygen molecules are also produced.
Water is absorbed by plants through their roots along with various nutrients in the soil. The water is used by the plant to transport the nutrients throughout the plant to wherever the nutrients are needed. During the process of photosynthesis, water is also used to break down the carbon dioxide molecules in order to make glucose.
Sunlight provides the energy that is needed for this biochemical process to occur. Plants capture this sunlight through chlorophyll pigments, which are the same pigments that give plant leaves and other plant parts their green color.
The carbon dioxide that the plant uses to make glucose through photosynthesis is captured from the air through microscopic openings (“stomata”) in the plant’s outer tissue layer (“epidermis”). The stomata open and close as the plants absorb carbon dioxide and release oxygen. Carbon dioxide in the air comes from a number of sources, including animal exhalation, decaying organic matter, volcanic eruptions, and fossil fuel emissions.
During the process of making glucose, the water molecules and carbon dioxide molecules are broken apart during a series of chemical reactions that are powered by the sun’s energy. Other chemical reactions build the glucose molecules from the original water and carbon dioxide atoms and also require the sun’s energy.
The glucose is used by the plant for growth as well as a little bit during the photosynthesis. The oxygen that is produced through the photosynthesis is essentially a waste product for the plant, and therefore is expelled by the plant’s stomata into the atmosphere.
This process of photosynthesis is part of a symbiotic relationship between plants and the animals on the Earth, who expel the carbon dioxide through respiration that the plants need for photosynthesis.