The three main things affecting the rate of photosynthesis are: 1.Light 2.Temperature 3.Carbon dioxide These three factors are called LIMITING FACTORS. 1. Light The rate of photosynthesis increases with increase in light intensity. Many plants spread out their leaves in such a way that each leaf maximises the amount of light falling on them. 2. Temperature The higher the temperature then typically the greater the rate of photosynthesis, photosynthesis is a chemical reaction and the rate of most chemical reactions increases with temperature.

However, for photosynthesis at temperatures above 40°C the rate slows down. This is because the enzymes involved in the chemical reactions of photosynthesis are temperature sensitive and destroyed at higher temperatures. To better understand the effects of temperature on photosynthesis it is important to know the effect of temperature on the enzymes involved in photosynthesis. Enzymes are affected a great deal by temperature.

If the temperature is too cold the enzymes move around too slowly to meet the substrate and for a reaction to occur.As the temperature increases though, so does the rate of reaction. This is because heat energy causes more collisions between the enzyme and the substrate.

However as you will remember all enzymes are proteins and at too high temperatures the proteins break down. The active site of the enzyme becomes distorted and so the substrate no longer fits and hence the reaction does not occur. It is then said that the enzyme has been denatured.

Plants from regions of warmer climates can successfully grow in colder regions by using greenhouses. The rate of photosynthesis does not increase with higher temperatures for all plants. Plants which grow in colder climates have an optimum rate of photosynthesis at low temperatures. Therefore different types of plants have optimum temperatures for photosynthesis. An increase in the concentration of carbon dioxide gives an increase in the rate of photosynthesis.