Photosynthesis occurs in 2 phases. In phases one, the light-dependent reactions, light energy is absorbed and then converted into chemical energy in the form of ATP and NADPH. In phase two, the light-independent reactions, the chemical energy stored in ATP and NADPH from phase one is used to make glucose. Once glucose is produced, it can be joined to other simple sugars to form larger molecules. These larger molecules are complex carbohydrates, such as starch. Carbohydrates are composed of repeating units of small organic molecules. The end products of photosynthesis also cab be used to make other organic molecules, such as proteins, lipids, and nucleic acids.