Photosynthesis: How Plants Turn Light Into Food

Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy stored in glucose. It's the basis of most food chains and produces most of the oxygen in our atmosphere.

The overall equation is deceptively simple: six molecules of carbon dioxide plus six of water, with light and chlorophyll, produce one molecule of glucose and six of oxygen. In reality, the process happens in many steps, mainly in two stages: the light-dependent reactions (in the thylakoid membranes) and the light-independent reactions, or Calvin cycle (in the stroma).

In the light reactions, chlorophyll absorbs photons and uses that energy to split water, releasing oxygen and producing ATP and NADPH. In the Calvin cycle, those energy carriers are used to fix CO2 into organic molecules, eventually building glucose.

Understanding photosynthesis helps us see why plants need light and water, why deforestation affects the climate, and how we might one day mimic it to produce clean fuel.