What is Photosynthesis?

Photosynthesis converts light energy into chemical energy, allowing plants to produce organic matter. It supports primary production in food webs and contributes to the global carbon cycle.

How do plants use light energy?

Photosynthesis usually takes place in chloroplasts in leaves. Chlorophyll and other pigments absorb light. In light-dependent reactions, water is used and oxygen is released, while energy carriers are produced for later steps. Carbon-fixation reactions help build organic molecules from carbon dioxide. These are connected stages made up of many enzyme-driven reactions. Carbon dioxide enters leaves mainly through stomata, and water travels from roots through vascular tissue. Light, temperature, water status, and carbon dioxide availability can jointly affect the rate of photosynthesis.

Photosynthesis in ecosystems

Sugars produced by plants support growth and respiration; some carbon is converted into starch, cellulose, and other compounds. Animals that eat plants transfer this chemical energy through food webs. Oxygen released during photosynthesis affects atmospheric composition and conditions for aerobic life. Plants do not store all the sugar they make: cells use some organic matter in respiration. Photosynthesis and respiration are distinct processes, and plants respire in light as well. Reducing photosynthesis to “plants make food from sunlight” leaves out the roles of water, gas exchange, and cellular reactions.