Coral polyps, which are animals, and zooxanthellae, the plant cells that live within them, have a mutualistic relationship. Coral polyps produce carbon dioxide and water as byproducts of cellular respiration. The zooxanthellae cells use the carbon dioxide and water to carry out photosynthesis. Sugars, lipids (fats) and oxygen are some of the products of photosynthesis which the zooxanthellae cells produce. The coral polyp then uses these products to grow and carry out cellular respiration. The tight recycling of products between the polyp cells and the zooxanthellae is the driving force behind the growth and productivity of coral reefs. This animation shows how the products created by the algal polyp and zooxanthellae cells are provided to each other for their mutual benefit.