Photosynthesis
Photosynthesis
- Photosynthesis is how plants make food (carbohydrates) using light energy.
- It needs light and chlorophyll.
- Learn the word equation exactly.
Practice
The word equation for photosynthesis is:
Plants take in CO₂ and water and make glucose and oxygen, using light and chlorophyll.
The equation and chlorophyll
$$\text{carbon dioxide} + \text{water} \rightarrow \text{glucose} + \text{oxygen}$$
- Chlorophyll (a green pigment in the chloroplasts) traps the light energy.
- Glucose is used to: store as starch, build cellulose, release energy in respiration, and move around as sucrose in the phloem.
Practice
Chlorophyll:
Chlorophyll traps light energy and transfers it to build carbohydrates; it is not used up.
Minerals and rate
- nitrate ions → make amino acids (proteins); magnesium ions → make chlorophyll.
- Rate depends on light intensity, CO₂ concentration and temperature.
- The factor in shortest supply is the limiting factor.
Practice
Magnesium ions are needed by a plant to make:
Magnesium → chlorophyll; nitrate → amino acids. A magnesium shortage gives yellow leaves.
Practice
The limiting factor for photosynthesis is:
At any moment, whichever of light, CO₂ or temperature is in shortest supply limits the rate.
You've got it
Key idea
- carbon dioxide + water → glucose + oxygen (needs light and chlorophyll)
- chlorophyll (in chloroplasts) traps light; glucose → starch/cellulose/respiration/sucrose
- nitrate → amino acids; magnesium → chlorophyll
- rate set by light, CO₂, temperature — the limiting factor is whichever is shortest