Solar radiation is ultimately the source of energy for almost all life on Earth. Plants - the base of every food chain and food web - use sunlight to create the chemical energy (food!) that supplies all other living organisms with energy. They do this through photosynthesis. The chemical energy organisms obtain as they consume other organisms is important for bodily functions. Cellular structures known as mitochondria convert glucose into other useful forms of energy to keep our bodies running properly. We even harness the energy stored in once-living organisms. We do this every time we burn fossil fuels such as coal, oil, and natural gas.