Photosynthesis
Photosynthesis is essentially the reverse process of cellular respiration. It absorbs light energy from the sun and converts it to sugars through endothermic reactions. Almost all organisms rely on photosynthesis either directly or indirectly. Organisms which produce their own food from inorganic food molecules are called autotrophs, and photoautotrophs are specifically those which get their energy from the sun (as opposed to chemoautotrophs, which get their energy from chemicals). Plants are photoautotrophs. In general, autotrophs are considered as the producers of the biosphere. On the other hand, organisms which consume other organisms are called heterotrophs. Animals, fungi, and many types of prokaryotes fall under this category. Now, let's take a closer look at the details of this process and the alternate mechanisms which are available for plants living under special conditions.