Photosynthesis and the leaf
Almost every food chain on Earth begins with a plant capturing light. Photosynthesis is the reaction that turns light energy into chemical energy stored in glucose.
Part of your national curriculum
- Biology: material cycles and energy: Understand the reactants in, and products of, photosynthesis, and a word summary for photosynthesis
Lesson overview
What you'll learn in this lesson
Understand the reactants in, and products of, photosynthesis, and a word summary for photosynthesis
Key learning points
- • The reaction
- • Leaf adaptations
- • Limiting factors
- • What happens to the glucose
This lesson at a glance
- 30 minutes
- 27 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 27
Visual introductionPicture this
Photosynthesis and the leaf
Almost every food chain on Earth begins with a plant capturing light. Photosynthesis is the reaction that turns light energy into chemical energy stored in glucose.
In a nutshell
Understand the reactants in, and products of, photosynthesis, and a word summary for photosynthesis
What you already know
Part 2 of 27
Before we start
What you already know
You should already know that plants need light and water, and that gases can move in and out of leaves.
Key words
Part 3 of 27
Key words
Words you'll need today
- Photosynthesis
- Plants making glucose from carbon dioxide and water using light.
- Chlorophyll
- The green pigment that absorbs light energy.
- Stomata
- Tiny pores, mostly under the leaf, that let gases in and out.
- Limiting factor
- The thing in shortest supply that holds the rate back.
- Starch
- The storage form plants turn glucose into.
Reset break
Part 4 of 27
Pause
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Learning cycle
Part 5 of 27
Learning cycle 1 of 2
The reaction and the leaf
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 6 of 27
Learn
The reaction
Carbon dioxide + water → glucose + oxygen, with light absorbed by chlorophyll in the chloroplasts. The reaction is endothermic: it takes in energy from light. Oxygen is a by-product released through the stomata, and it is the source of almost all the oxygen in the atmosphere.
Explore the idea
Part 7 of 27
Learn
Leaf adaptations
Leaves are broad and flat for a large surface area, thin so gases diffuse quickly, and packed with chloroplasts in the upper palisade layer where light is strongest. Air spaces in the spongy layer let carbon dioxide reach the cells, and veins bring water and carry glucose away.
Reset break
Part 8 of 27
Pause
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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 9 of 27
Quick check
Part 10 of 27
Learning cycle
Part 11 of 27
Learning cycle 2 of 2
Rate and what glucose is for
A short piece of teaching, then a check to make sure it has landed.
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Part 12 of 27
Pause
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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 13 of 27
Learn
Limiting factors
The rate of photosynthesis is limited by light intensity, carbon dioxide concentration and temperature. Increasing light raises the rate until another factor becomes limiting and the graph levels off. Beyond about 40 °C the rate falls sharply because the enzymes involved are denatured.
Explore the idea
Part 14 of 27
Learn
What happens to the glucose
Glucose is used in respiration to release energy, converted to starch for storage, used to make cellulose for cell walls, or combined with nitrates absorbed from the soil to make proteins. A plant short of nitrates grows poorly with yellowing leaves, even in bright light.
Quick check
Part 15 of 27
Reset break
Part 16 of 27
Pause
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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 17 of 27
Explore the idea
Part 18 of 27
Worked example
Worked answer: a graph of photosynthesis rate against light intensity rises then levels off. Explain (3 marks)
At low intensity light is the limiting factor, so adding more light increases the rate proportionally (1). At higher intensity the graph plateaus because light is no longer limiting (1); something else, such as carbon dioxide concentration or temperature, is now restricting the rate (1). Saying the plant is 'full of light' describes nothing scientific.
Common mix-ups
Part 19 of 27
Common mix-ups
Things people often get wrong
- People often think plants only photosynthesise and never respire. Plants respire all the time, day and night.
- People often think plants take their food from the soil. Their food is glucose they make themselves; soil supplies minerals.
Reset break
Part 20 of 27
Pause
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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 21 of 27
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
Challenge round
Part 22 of 27
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
The ____ is endothermic: it takes in energy from light.
The rate of ____ is limited by light intensity, carbon dioxide concentration and temperature.
Challenge round
Part 23 of 27
Game · Recall cards
An arrow in a food chain points…
Card 1 of 4
Reset break
Part 24 of 27
Pause
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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.
Exit quiz
Part 25 of 27
Exit quiz
Show what you've learned
6 questions, marked together at the end. Nothing is timed.
1. The reactants of photosynthesis are...
2. Chlorophyll is found inside...
3. Stomata mainly allow...
4. On a bright, warm day with little carbon dioxide, the limiting factor is likely...
5. Plants store glucose as...
6. Which statement is true?
Mastery quiz
Part 26 of 27
Marked quiz
End of lesson quiz: Photosynthesis and the leaf
4 questions, marked with the reasoning shown. No timer.
1. An arrow in a food chain points…
2. Roughly how much energy passes to the next trophic level?
3. Removing a top predator most likely…
4. The word equation for photosynthesis is
Lesson round-up
Part 27 of 27
Lesson round-up
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Understand the reactants in, and products of, photosynthesis, and a word summary for photosynthesis