We measure transpiration using a potometer. As water moves up through the plant, the air bubble moves along the scale - giving a measure of water absorbed by the plant over time and thus the transpiration rate.We can create many conditions to see how the factors affect the plant and rate of transpiration:
- Temperature (heat lamp) - an increase in the temperature warms the water in the leaves causing it to evaporate more quickly, and also increases the capacity of air to absorb more water.
- Sunlight (sun - window/lamp) - same effect as temp. because of warmed leaves. Causes stomata to open and thus a higher transpiration rate to that of a cold day.
- Wind (fan/hairdryer) - transpiration relies on diffusion. In windy conditions the air molecules are blown away from the leaves preventing air around the leaves becoming saturated with water molecules.
- Humidity - lows transpiration. This is the concentration of water vapour in the air. Low humidity = low concentration and a good concentration gradient which helps the transport of water by diffusion. High humidity = air around leaves is already saturated and a higher concentration of water molecules than inside the leaves. (SEE BBC BITESIZE FOR A GOOD TABLE)
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