Transpiration Edexcel International GCSE Biology revision
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In plain words
Plants are always losing water. It evaporates inside the leaves and escapes as vapour through the stomata. That loss pulls more water up from the roots, like drinking through a straw. On a hot, windy day a big tree can lose hundreds of litres.
Three things to know
- Transpiration is the loss of water vapour from the leaves. Water evaporates from the surfaces of the mesophyll cells into the air spaces, then diffuses out through the stomata.
- As water leaves, more is pulled up the xylem in an unbroken column: the transpiration pull. Water molecules stick to each other (cohesion), which holds the column together.
- Transpiration is faster when it is warmer, windier, brighter or drier. A plant wilts when it loses water faster than its roots can replace it.
Tips and tricks
- Two steps, in order: evaporation from the cells, then diffusion out through the stomata.
- Wind speeds it up by blowing away the damp air round the leaf, which keeps the concentration gradient steep.
It lands in your notebook with its questions as flashcards.
Transpiration: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
Through which structures does most water vapour leave a leaf?
Stomata are the pores in the leaf surface.
Which condition slows transpiration?
Damp air makes the concentration gradient smaller.
What pulls water up the xylem?
Water lost from the leaves draws more up behind it.
Why does water move up the xylem as an unbroken column?
This attraction is called cohesion.
What apparatus measures the rate of water uptake by a shoot?
The movement of a bubble along a tube shows how fast water is taken up.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 7 marks. Write your answers on paper, then check them.
Transpiration
Edexcel International GCSE Biology 4BI1 · 7 marks · papermunch.org
Name ______________________________ Date ______________
State what is meant by transpiration.[2]
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The loss of water vapour from a plant's leaves, by evaporation from the mesophyll cells followed by diffusion out through the stomata.
Explain why transpiration is faster on a warm, windy day.[3]
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Warmth gives water molecules more energy, so evaporation and diffusion are faster. Wind carries away the water vapour near the leaf, keeping the concentration gradient steep.
Explain why a plant wilts on a hot day.[2]
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It loses water by transpiration faster than it can take it up, so its cells lose water and become flaccid.
Answers: Transpiration
- 1. The loss of water vapour from a plant's leaves, by evaporation from the mesophyll cells followed by diffusion out through the stomata.
- 2. Warmth gives water molecules more energy, so evaporation and diffusion are faster. Wind carries away the water vapour near the leaf, keeping the concentration gradient steep.
- 3. It loses water by transpiration faster than it can take it up, so its cells lose water and become flaccid.