The model of photosynthesis used by biologists begins when chlorophyll splits a water molecule into hydrogen and oxygen. The oxygen from the water is a waste product that is released as a gas. In later stages of photosynthesis, carbon dioxide from the air and hydrogen from the water unite to form glucose. Photosynthesis usually takes place in the leaves of green plants. The food produced is a simple sugar called glucose. Some of the food made during photosynthesis is used by plants for their growth and development. The rest is stored in the plant.