Albert Teen

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Rate of Transpiration

# Rate of Transpiration

### Rate of Transpiration

Temperature, humidity, air movement and light intensity all have an affect on the rate of transpiration.

Which keyword is this the definition of? The evaporation of water from the surface of a plant.

What do you think we actually mean when we talk about the rate of transpiration?

1

We use a potometer to estimate the rate of transpiration

The potometer measures the water uptake by the plant, which is approximately equal to the amount of water that the plant loses in transpiration.

2

Look at the diagram. What do you think we actually measure in this experiment to determine how much water the plant takes up?

A) How far the bubble moves in a minute B) How much water was removed from the beaker in a minute

3

Estimating the transpiration rate

The distance the bubble moves every minute is an estimate of the rate of transpiration in a minute.

If a bubble in a potometer travelled 35mm in 5 minutes what would the rate of transpiration be?

Temperature affects the rate of transpiration. How do you think the transpiration rate on a hot day will be different to the transpiration rate on a cold day?

Light intensity also affects the rate of transpiration. What do you think the rate of transpiration would be like on a brighter day compared to a dull day?

In hotter temperatures, the water molecules have more energy, so they evaporate faster, increasing the rate of transpiration.

In brighter conditions, more photosynthesis happens. Therefore the stomata (pores) are open and the rate of transpiration is faster.

How do you think windy conditions affect the rate of transpiration? Windier conditions will ___________ the rate.

Wind blows water molecules away, so the concentration of water is low outside of the leaf. The water gradient (difference in concentration) is high, because the concentration of water inside the leaf is much higher than outside. This makes diffusion faster, so transpiration **** is also faster.

When humidity is higher, there is more water vapour in the air, like on a foggy day. When humidity is lower the air is drier. Do you think the rate of transpiration is higher when it is more humid or less humid?

When it is more humid there is more water vapour in the air, and the water gradient (difference in concentration) is low. This means that the concentration of water inside the leaf and outside of the leaf is similar. This makes diffusion slower, so transpiration is also slower.