Concept preview

What you will be able to do

1. 01Explain how light intensity, carbon dioxide concentration and temperature limit the rate of photosynthesis.
2. 02Interpret limiting-factor graphs and apply the idea of a limiting factor.
3. 03Explain the compensation point and what it means for a plant.
4. 04Compare and contrast cellular respiration and photosynthesis in reactants, products, location and energy flow.

Photosynthesis is not a single event but a rate, a speed at which a leaf turns carbon dioxide and water into sugar, and that speed can rise and fall depending on the conditions. Three environmental conditions matter most: the light intensity, the carbon dioxide concentration, and the temperature. Each of these is a raw material or a condition the reactions need, and at any given moment the process can go only as fast as the least favourable of them allows. Understanding these factors is not just an exam exercise; it is the science that lets a grower in a greenhouse or a farmer in a field push a crop to grow faster, and it explains why the same plant photosynthesises briskly on a warm bright morning and barely at all on a cold, dim afternoon.