Photosynthesis explained
Photosynthesis is how plants, algae and some bacteria turn light into chemical energy. It happens inside chloroplasts, where the green pigment chlorophyll absorbs mostly red and blue light.
6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂
The two stages
Light-dependent reactions take place in the thylakoid membranes. Light energy splits water, releasing oxygen and producing ATP and NADPH.
The Calvin cycle takes place in the stroma. It uses ATP and NADPH to fix carbon dioxide into glucose.
What limits the rate?
Light intensity, carbon dioxide concentration and temperature. If one is in short supply, it caps the rate no matter how much of the others is available.
Exam tip: Oxygen comes from the splitting of water, not from carbon dioxide.