2.19 understand how varying carbon dioxide concentration, light intensity and temperature affect the rate of photosynthesis

Carbon dioxide
If there is not enough (insufficient) carbon dioxide, the rate of photosynthesis will decrease. This is because there is less reactant (carbon dioxide), therefore less reaction.

If there is lots of carbon dioxide the rate of photosynthesis will be much higher, as there will be lots of reactant.

Light Intensity
If the light intensity is low the rate of photosynthesis decreases because the energy that the light provides is less, therefore the rate of reaction is decreased.

Alternatively, if the light intensity is high the rate of photosynthesis will increase as the light is providing more energy meaning the rate of reaction will increase.

Temperature
In cold temperatures, the rate of photosynthesis would decrease as the molecules of carbon dioxide and water would have less energy meaning they would collide less (the rate of reaction would be slower).

In hot conditions, the rate of photosynthesis would be faster as molecules would have more energy. However, too high a temperature could have devastating effect. For example, the enzymes could denature/plant could wilt/too much transpiration etc