Energy for Life 4.5-4.7 The Sun and Photosynthesis: How We Get Energy All activities by living things require energy. Consumers get their energy from the foods that they eat, but where do the producers get their energy? Organisms can’t use light energy directly as a source of food. Photosynthesis convert light energy from the sun into chemical energy that is stored in sugar molecules. This energy can be used by plants themselves or organisms that eat the plant. First, the plant must absorb light energy using chlorophyll, a green pigment that gives plants their color. CO2 and water is also absorbed. Light energy breaks down the water into hydrogen and oxygen. The hydrogen then combines with the CO2 to form sugar molecules. The oxygen is released into the air. The energy used to form the sugar is stored in chemical bonds. When the bonds are broken, energy is release. Energy is used to carry out the cells activities. Energy is Released as Food is Broken Down The major energy releasing process is cellular respiration. During this process sugar is broken down and energy is released. The chemical energy in food is also released by chemical reactions. ATP, the Cell’s Currency for Energy Transfer Cellular respiration converts the energy stored in complex molecules into chemical energy stored in ATP, adenosine triphosphate. Each ATP molecule is made up of a sugar complex attached to three phosphates. Energy is stored in ATP until it is released by reactions that remove one of the phosphates. Each ATP molecule releases energy whenever a phosphate is broken off or transferred to another molecule. The molecule that remains has only two phosphate groups and is called ADP, adenosine diphosphate.