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SavannahYear 8
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ScienceBiology foundations for GCSE (AQA 8461)30 min★★★ difficulty

Photosynthesis and respiration as an energy pair

The two equations look like mirror images, and students often assume they cancel out. They do not — and understanding why is the heart of bioenergetics.

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 word equations
  • • Why they do not cancel
  • • Where the glucose goes
  • • Limiting factors

This lesson at a glance

  • 30 minutes
  • 19 parts to scroll through
  • 4 quick checks
  • Marked quiz at the end
  • Gentle pace: short sittings with pauses

Words to know

reactantsproductsphotosynthesissummaryequations

Scroll down — the lesson carries on below

Part 1 of 19 · Discover5%
1

Watch & discover

Part 1 of 19

Watch first

Photosynthesis and respiration as an energy pair

Follow how your cells use glucose and oxygen to release energy.

In a nutshell

Understand the reactants in, and products of, photosynthesis, and a word summary for photosynthesis

2

What you already know

Part 2 of 19

Before we start

What you already know

You should already know that plants make food using light and that all living things respire.

3

Key words

Part 3 of 19

Key words

Words you'll need today

Photosynthesis
Light energy converted to chemical energy in glucose.
Respiration
Releasing energy from glucose in every living cell.
Limiting factor
The factor currently holding back the rate.
Chlorophyll
The green pigment that absorbs light for photosynthesis.
Endothermic
A process that takes in energy from its surroundings.
4

Learning cycle

Part 4 of 19

Learning cycle 1 of 2

Two equations, two purposes

A short piece of teaching, then a check to make sure it has landed.

5

Explore the idea

Part 5 of 19

Learn

The word equations

Carbon dioxide + water → glucose + oxygen, driven by light and chlorophyll, is photosynthesis: endothermic, in chloroplasts, in the light. Glucose + oxygen → carbon dioxide + water is aerobic respiration: exothermic, in mitochondria, every cell, all the time.

6

Explore the idea

Part 6 of 19

Learn

Why they do not cancel

A plant photosynthesises faster than it respires during the day, so it accumulates biomass. At night only respiration runs. Net gas exchange therefore reverses across a 24-hour cycle, which is a favourite exam trap.

7

Quick check

Part 7 of 19

Quick check

Photosynthesis takes place in...

8

Quick check

Part 8 of 19

Quick check

Which is exothermic?

9

Reset break

Part 9 of 19

Pause

That's sitting 1 of 2 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.

Stop here for now
10

Learning cycle

Part 10 of 19

Learning cycle 2 of 2

Rates and limiting factors

A short piece of teaching, then a check to make sure it has landed.

11

Explore the idea

Part 11 of 19

Learn

Where the glucose goes

Glucose is used in respiration, converted to starch for storage, built into cellulose for cell walls, turned into lipids in seeds, or combined with nitrates to make amino acids. 'Plants make food' is true but far too vague at this level.

12

Explore the idea

Part 12 of 19

Learn

Limiting factors

Light intensity, carbon dioxide concentration and temperature can each limit the rate. Increase light and the rate rises, then plateaus when something else becomes limiting. Above about 40 °C the rate collapses because enzymes denature — that is not a plateau, it is a fall.

13

Quick check

Part 13 of 19

Quick check

A rate graph plateaus because...

14

Quick check

Part 14 of 19

Quick check

Glucose is stored in plants as...

15

Common mix-ups

Part 15 of 19

Common mix-ups

Things people often get wrong

  • Plants respire all the time, not only at night.
  • A plateau on a light-intensity graph means another factor is limiting, not that light stopped mattering.
  • Photosynthesis takes in energy; respiration releases it.
16

Challenge round

Part 16 of 19

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

17

Challenge round

Part 17 of 19

Game · Fill the gaps

Finish the sentences

Choose the word that belongs in each gap.

Carbon dioxide + water → glucose + oxygen, driven by light and chlorophyll, is ____: endothermic, in chloroplasts, in the light.

18

Mastery quiz

Part 18 of 19

Marked quiz

End of lesson quiz: Photosynthesis and respiration as an energy pair

6 questions, marked with the reasoning shown. No timer.

  1. 1. Reactants of photosynthesis are...

  2. 2. Respiration occurs in...

  3. 3. Above 40 °C the rate falls because...

  4. 4. Amino acids need glucose plus...

  5. 5. At night a plant...

  6. 6. Photosynthesis is described as...

19

Lesson round-up

Part 19 of 19

Lesson round-up

Ready when you are

Quiz score

Not sat

Games

Not played

Points this lesson

0

Best run

0 in a row

Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?

Ask Luna

Do the work

Your written work for this lesson

This is the part you'd do in your book at school. Pick the pieces below, write here or on paper, and photograph anything you draw or work out.

Case study

Why the school greenhouse failed

A science club grew tomato plants in the school greenhouse. In June the plants grew well: leaves were dark green and the fruit set quickly. In July the club went away for two weeks and left the greenhouse door shut. When they came back, the leaves were curled and pale and most of the fruit had dropped.

The club had a data logger inside. It showed the temperature reached 46 °C on several afternoons and the soil moisture fell close to zero. The club knew photosynthesis needs light, water and carbon dioxide, and that enzymes in a plant work best in a narrow range of temperature. Above that range the enzymes stop working properly.

The club repeated the summer with the door propped open and a water bottle drip on each pot. Temperature peaked at 31 °C and the plants survived.

Written for Good Learning Co.

Reading questions

  1. Name the variable the club changed the second time, and one variable they kept the same.
  2. Explain, using the words photosynthesis and enzymes, why the plants were damaged in July.
  3. Write a conclusion for the club's report, saying how far the evidence supports it.

  • Method and results

    Writing

    Write the aim, what you changed, what you measured and what you kept the same, then record your results in a table.

    1 page + results table

  • Conclusion

    Writing

    Explain what your results show and why, using the scientific words from the lesson. Say how you know you can trust them.

    6–8 sentences

  • Labelled diagram

    Diagram

    Draw the apparatus or the process in pencil, label it fully, and photograph it.

    1 labelled diagram

  • Reading and notes

    Reading

    Read the lesson text again and write the key ideas in your own words.

    Half a page of notes

Saved as you type.

Part 1 of 19 · Watch & discover

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