Assumed audience
General adult who has completed Plant Anatomy Fundamentals.
The overall reaction
6CO2 + 6H2O + light energy → C6H12O6 + 6O2. Plants use carbon dioxide and water, powered by sunlight, to produce sugars and release oxygen. This is photosynthesis.
Where it happens
Photosynthesis occurs in chloroplasts, specifically in the thylakoid membranes (light reactions) and the stroma (Calvin cycle).
Light-dependent reactions
Chlorophyll absorbs light, splits water molecules, produces ATP and NADPH, and releases oxygen.
Calvin cycle (light-independent reactions)
ATP and NADPH drive the fixation of CO2 into three-carbon sugars. These sugars are then used to build glucose and other organic molecules.
The stomatal trade-off
Stomata must open to admit CO2 but lose water when they do. Plants constantly balance carbon gain against water loss. This is especially challenging in hot, dry environments.
C3, C4, and CAM
Three strategies plants have evolved to manage the trade-off. C3 is the default. C4 (corn, sugarcane) concentrates CO2 to reduce photorespiration. CAM (cacti, succulents) opens stomata only at night.
Why this matters
Photosynthesis is the energetic foundation of nearly all life on Earth. Understanding it explains plant growth, agricultural productivity, and the carbon cycle.