Factors affecting the rate of transpiration:

1. The rate of transpiration is directly controlled by the opening and closing of stomata and it is under the influence of light. In strong light, the rate of transpiration is very high as compared to dim light or no light. Other factors which affect the rate of transpiration are given below.
2. Higher temperature reduces the humidity of the surroundings and also increases the kinetic energy of water molecules. In this way, it increases the rate of transpiration. The rate of transpiration doubles with every rise of 10°C in temperature. But very high temperatures i.e., 40-45°C cause closure of stomata, so that transpiration stops, and the plant does not lose the much-needed water.
3. When air is dry, water vapors diffuse more quickly from the surface of mesophyll cells into leaf air spaces and then from air spaces to outside. This increases the rate of transpiration. In humid air, the rate of the diffusion of water vapors is reduced and the rate of transpiration is low.
4. Wind (air in motion) carries the evaporated water from leaves, and it causes an increase in the rate of evaporation from the surfaces of mesophyll. When air is still, the rate of transpiration is reduced.
5. The rate of transpiration also depends upon the surface area of the leaf. More surface area provides more stomata and there is more transpiration.