What photosynthesis is (spec 2.18)
Light energy is captured and stored as chemical energy in glucose.
Photosynthesis is the process by which green plants make their own food. It is the reaction that turns the energy in sunlight into food energy for almost every food chain on Earth.
- It happens in the chloroplasts of plant cells, which contain the green pigment chlorophyll.
- Chlorophyll absorbs light energy (mainly from the Sun).
- That light energy is converted into chemical energy, which is stored in the bonds of the glucose (a carbohydrate) that is made.
So photosynthesis is really an energy conversion: light energy → chemical energy. Because plants make their own food this way, they are described as autotrophic.
Why it matters. The glucose made can be:
- used in respiration to release energy, or
- converted to starch for storage, or to cellulose for cell walls, or to other molecules.
Exam tip. When a question asks what photosynthesis is, the marking point is the energy conversion — say "light energy is converted (by chlorophyll) into chemical energy stored in glucose/carbohydrate". Don't just list the ingredients.
- Photosynthesis converts light energy into chemical energy.
- Chlorophyll in chloroplasts absorbs the light energy.
- The chemical energy is stored in glucose (a carbohydrate).
See the full worked example for photosynthesis process and factors affecting it →