Inside a leaf: stomata and the gas trade
A leaf is a solar panel with a breathing problem. It needs carbon dioxide from the air, but every opening that lets gas in also lets water vapour out.
Part of your national curriculum
- Biology: material cycles and energy: Understand the role of leaf stomata in gas exchange in plants and the dependence of almost all life on Earth on the ability of photosynthetic organisms to use sunlight
Lesson overview
What you'll learn in this lesson
Understand the role of leaf stomata in gas exchange in plants and the dependence of almost all life on Earth on the ability of photosynthetic organisms to use sunlight
Key learning points
- • The layers of a leaf
- • Stomata: adjustable pores
- • Why the rest of life depends on this
This lesson at a glance
- 25 minutes
- 20 parts to scroll through
- 4 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 20
Visual introductionPicture this
Inside a leaf: stomata and the gas trade
A leaf is a solar panel with a breathing problem. It needs carbon dioxide from the air, but every opening that lets gas in also lets water vapour out.
In a nutshell
Understand the role of leaf stomata in gas exchange in plants and the dependence of almost all life on Earth on the ability of photosynthetic organisms to use sunlight
Learning cycle
Part 2 of 20
Learning cycle 1 of 2
Part 1 · The layers of a leaf
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 3 of 20
Learn
The layers of a leaf
Light passes through a thin waxy cuticle and a clear upper layer, then reaches the palisade cells packed with chloroplasts. Below them, spongy cells sit in a maze of air spaces so gases can reach every cell.
Reset break
Part 4 of 20
Pause
That's sitting 1 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Explore the idea
Part 5 of 20
Learn
Stomata: adjustable pores
Most stomata are on the underside of the leaf. Each pore sits between two guard cells. When the guard cells swell with water they curve apart and the pore opens; when the plant is short of water they slacken and the pore closes, protecting the plant but pausing photosynthesis.
Quick check
Part 6 of 20
Quick check
Part 7 of 20
Reset break
Part 8 of 20
Pause
That's sitting 2 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Learning cycle
Part 9 of 20
Learning cycle 2 of 2
Part 2 · Why the rest of life depends on this
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 10 of 20
Learn
Why the rest of life depends on this
Photosynthetic organisms — plants, algae and some bacteria — are the only large-scale route by which sunlight energy enters food chains. Almost every other organism, including us, eats that captured energy second-hand and breathes the oxygen released as a by-product.
Quick check
Part 11 of 20
Reset break
Part 12 of 20
Pause
That's sitting 3 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Quick check
Part 13 of 20
Explore the idea
Part 14 of 20
Worked example
Worked example: explaining a wilting plant
A plant left unwatered on a hot windowsill grows slowly even though it has plenty of light. Explanation: water loss is high, so guard cells close the stomata to conserve water. With the pores closed, carbon dioxide cannot diffuse in, so the rate of photosynthesis falls and growth slows — light was never the limiting factor.
Challenge round
Part 15 of 20
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Reset break
Part 16 of 20
Pause
That's sitting 4 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Challenge round
Part 17 of 20
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
Most ____ are on the underside of the leaf.
Photosynthetic organisms — ____, algae and some bacteria — are the only large-scale route by which sunlight energy enters food chains.
____ every other organism, including us, eats that captured energy second-hand and breathes the oxygen released as a by-product.
Challenge round
Part 18 of 20
Game · Recall cards
What gas do stomata mainly let into the leaf for photosynthesis?
Card 1 of 4
Mastery quiz
Part 19 of 20
Marked quiz
End of lesson quiz: Inside a leaf: stomata and the gas trade
4 questions, marked with the reasoning shown. No timer.
1. What gas do stomata mainly let into the leaf for photosynthesis?
2. What controls the opening and closing of stomata?
3. Why are photosynthetic organisms essential to almost all life on Earth?
4. Where are most stomata found?
Lesson round-up
Part 20 of 20
Lesson round-up
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Understand the role of leaf stomata in gas exchange in plants and the dependence of almost all life on Earth on the ability of photosynthetic organisms to use sunlight