Effect of the Environment
The movement of water through the plant is driven by evaporation of water from the leaf. Factors which affect the rate of evaporation will also affect the rate of transpiration.
A piece of apparatus called a potometer can be used to investigate water loss from a plant in different environmental conditions. The effect of temperature, humidity, wind speed and light intensity can therefore be looked at.
- Temperature - the hotter it is the faster the rate of evaporation and therefore transpiration.
- Light Intensity - light causes the stomatal pores to open for photosynthesis. This also means that water can be lost. The pores close at night, so reducing water loss.
- Humidity - the air can only hold so much moisture. If the air is already humid then it is harder for water to evaporate than if the air was dry.
- Wind speed - in still air, the air around the leave becomes humid and a micro-climate is set up which reduces the rate of evaporation. As the wind speed increases the humid air around the leave is replaced by drier air and so the micro-climate is removed. The faster the wind speed the quicker dry air can replace the humid air and so the greater the rate of evaporation.
If the rate of water loss is higher than the intake the plant will start to wilt. This is because the cells of the plant lose their turgidity and go flaccid.
