Photosynthesis. we know several things about this process. first, it is driven by light, usually sunlight. it is preformed by autotrophs in an ecosystem, and we usually think of plants in this regard. now think of earth as a closed system to energy. sunlight reaches both sides of the lake in this picture but under different circumstances. on the left, there are dark clouds and rain, water in the atmosphere. on the right, it is sunny with cumulous clouds that are not rain clouds or dark