Green plants use sunlight to make glucose.
To do so, the plant must use carbon dioxide and water in a process called photosynthesis. The glucose made by plants is used by plants and animals as a source of energy. The process by which ATP is made from glucose is called cellular respiration. Respiration also produces waste products including carbon dioxide and water, which are the same substances that served as raw materials for photosynthesis. In water, carbon dioxide dissolves to form a weak acid.