Through three. Listen to part of a lecture in a botany class. The professor is discussing photosynthesis. The complex process inside a leaf takes energy from the sun and uses it to convert water and carbon dioxide into sugars. During this process, photosynthesis plants convert light energy into chemical energy. All leaves carry out photosynthesis. And basically the same way, first the pores on the leaves, outer skin open up and taking molecules of carbon dioxide. Water absorbed by the roots is transported upward through the plant, and it enters the leaf through its stem, carbon dioxide and water. These are the raw materials for photosynthesis. Once carbon dioxide and water are present, photosynthesis can begin. The chemical reactions of photosynthesis take place in two stages, the light dependent reactions and the light independent reactions. When sunlight shines on a leaf during the light dependent stage, its energy is absorbed by molecules of chlorophyll, which you all know is the pigment giving a leaf its green color. The light energy absorbed by the chlorophyll is used to split the hydrogen and oxygen in the water. Then during the light independent reactions, hydrogen from the water combines with carbon dioxide and forms carbohydrates, including the sugar glucose, but also other molecules that are rich in food energy for the plant. In the process, access oxygen is released to the outside air through the leaves pores. Finally, the plant transports the products of photosynthesis. Microscopic veins in the leaf carry the food out through the stem and into the cells of the plant. This process continues all throughout the growing season. That is as long as the leaves remain green.