Gas exchange in plants Edexcel International GCSE Biology revision
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In plain words
Plants respire all the time, like you, taking in oxygen and giving out carbon dioxide. But in the light they also photosynthesise, which does the opposite, and much faster. So which gas a leaf is taking in depends on how bright it is.
Three things to know
- Gases move in and out of a leaf by diffusion through the stomata. Guard cells open them in the light and close them in the dark.
- In bright light, photosynthesis is faster than respiration: the leaf takes in carbon dioxide and gives out oxygen. In the dark, only respiration happens: it takes in oxygen and gives out carbon dioxide.
- Hydrogen-carbonate indicator shows the change: orange in normal air, yellow when there is more carbon dioxide, purple when there is less.
Tips and tricks
- Plants respire all day and all night. They don't stop respiring when they photosynthesise.
- Indicator colours: more carbon dioxide, yellow; less carbon dioxide, purple.
It lands in your notebook with its questions as flashcards.
Gas exchange in plants: 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 do gases enter and leave a leaf?
Stomata are pores, mostly on the underside.
In the dark, which gas does a leaf give out?
Only respiration is happening.
In bright light, what is the net gas exchange of a leaf?
Photosynthesis outpaces respiration.
What colour is hydrogen-carbonate indicator when carbon dioxide levels are high?
More carbon dioxide makes it more acidic.
When do plants respire?
Every living cell respires all the time.
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.
Gas exchange in plants
Edexcel International GCSE Biology 4BI1 · 7 marks · papermunch.org
Name ______________________________ Date ______________
Explain why a leaf gives out oxygen in bright light.[2]
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Photosynthesis is faster than respiration, so more oxygen is made than is used.
A leaf is sealed in a tube with orange hydrogen-carbonate indicator and left in the dark. State and explain the colour change.[3]
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It turns yellow. In the dark the leaf only respires, releasing carbon dioxide, so the carbon dioxide concentration rises.
Describe how gases get into and out of a leaf.[2]
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By diffusion through the stomata, which are opened and closed by guard cells.
Answers: Gas exchange in plants
- 1. Photosynthesis is faster than respiration, so more oxygen is made than is used.
- 2. It turns yellow. In the dark the leaf only respires, releasing carbon dioxide, so the carbon dioxide concentration rises.
- 3. By diffusion through the stomata, which are opened and closed by guard cells.