The primary source of outside energy is the sun. The sun, through symbiotic green bacteria inside plant cells, is the only begetter of energy for all the life we can see with the unaided eye. Its energy is trapped by green solar panels (leaves) and used to drive uphill the synthesis of organic compounds, such as sugar and starch in plants. In a series of energy-coupled downhill and uphill chemical reactions, the rest of life is then powered by the energy originally trapped from the sun by plants.
