Why is "Confusing 'breathing' with 'respiration'" a common mistake in Investigating breathing in humans?

Why it happens: Both words are used loosely in everyday English and sound similar. How to avoid it: **Breathing** = moving air in and out of the lungs. **Respiration** = the chemical release of energy in cells. Exercise speeds up both, but they are not the same thing. Source: Edexcel Biology examiner reports

Why is "Saying 'exhaled air contains CO₂' without comparing to inhaled air" a common mistake in Investigating breathing in humans?

Why it happens: Students answer the easier 'does it contain CO₂' instead of the actual comparison question. How to avoid it: The question is comparative: state that exhaled air has **MORE** CO₂ **than inhaled air**, and that its limewater goes milky **faster**. Source: Edexcel Biology examiner reports 2022–2024

Why is "Saying limewater 'changes colour' or goes a specific colour" a common mistake in Investigating breathing in humans?

Why it happens: Students confuse limewater with coloured indicators. How to avoid it: Limewater is colourless and goes **cloudy / milky / white** with CO₂. Only the **hydrogencarbonate indicator** changes colour (red → yellow). Source: Edexcel Biology examiner reports

Why is "Explaining the exercise result with only 'the body needs more energy'" a common mistake in Investigating breathing in humans?

Why it happens: It feels like a complete answer but skips the biology. How to avoid it: Link the chain: muscles **respire faster** → need **more oxygen** and make **more CO₂** → so breathing rate and depth increase to supply O₂ and remove CO₂. Source: Edexcel Biology examiner reports

Why is "Forgetting to state a control variable / fair test" a common mistake in Investigating breathing in humans?

Why it happens: Students focus on the steps and skip making it a valid comparison. How to avoid it: Always state at least one control: **same person**, and **same type, time and intensity** of exercise. Add repeats and a mean for reliability. Source: Edexcel Biology examiner reports

Why is "Giving breathing rate without 'per minute' (not a rate)" a common mistake in Investigating breathing in humans?

Why it happens: Students count breaths but forget rate needs a time unit. How to avoid it: A **rate** must be per unit time — count and state breaths **per minute**. A bare number of breaths is not a rate. Source: Edexcel Biology examiner reports

Edexcel IGCSE Science(Double Award)-Biology (4WSD0-1B)

Investigating breathing in humans

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Detailed Study Notes

Detailed notes on Gas Exchange Function of Living Organisms for Edexcel IGCSE Science(Double Award)-Biology, covering key concepts, explanations, examples, and exam-focused revision points.

Investigating Breathing in Humans — Edexcel International GCSE Science (Double Award) Biology (4WSD0-1B) Study Notes

The required practical (spec 2.50): show that exhaled air contains more carbon dioxide than inhaled air using limewater (or hydrogencarbonate indicator), and investigate the effect of exercise on breathing rate and depth. Method, results, conclusions and the practical-skills marks — for Biology Paper 1 (4WSD0/1B).

At a glance

Two parts: (1) show exhaled air has more CO₂ than inhaled air; (2) show exercise increases breathing rate and depth.
Limewater goes cloudy/milky with CO₂ — exhaled air turns it milky faster than inhaled air.
Hydrogencarbonate indicator also detects CO₂: it changes red → orange → yellow as CO₂ rises.
Two-tube setup: breathe in and out through a T-piece so inhaled air bubbles through one tube and exhaled air through the other.
Breathing rate = number of breaths per minute; depth = how much air per breath.
Result: breathing rate (and depth) rise during/after exercise — count breaths for 1 minute before and after.
Why they rise: muscles respire more, need more oxygen and produce more CO₂, so breathing increases to supply O₂ and remove CO₂.
Fair test: same person, same exercise time/intensity, rest before the 'before' reading — repeat and find a mean.

What you’ll learn

Mapped to the Edexcel IGCSE 4SD0 syllabus (2026 onwards).

2.50 (practical) — Investigate breathing in humans, including the release of carbon dioxide and the effect of exercise.

Part 1: showing exhaled air contains more CO₂ (the apparatus)

Bubble inhaled and exhaled air through limewater and compare.

The first investigation shows that the air we breathe out contains more carbon dioxide than the air we breathe in.

The chemical test for carbon dioxide:

Limewater (calcium hydroxide solution) turns cloudy / milky when carbon dioxide is bubbled through it. The more CO₂, the faster and more strongly it goes milky.
Hydrogencarbonate indicator is an alternative: it starts red, turns orange in moderate CO₂, and yellow in high CO₂.

The two-tube apparatus:

Two test tubes (or boiling tubes) each contain limewater, joined by a central T-piece / mouthpiece.
Tube A is connected so that when you breathe IN, air is drawn in through tube A — this is inhaled (atmospheric) air.
Tube B is connected so that when you breathe OUT, air is pushed out through tube B — this is exhaled air.
Breathe gently in and out through the mouthpiece for a fixed time.

Inhaled air bubbles through tube A; exhaled air bubbles through tube B. Exhaled air turns its limewater milky much faster.

Exam tip. The valve/tube arrangement only matters in that one tube samples inhaled air and the other samples exhaled air through the same liquid — so it is a fair comparison.

Limewater goes cloudy/milky with CO₂; hydrogencarbonate indicator goes red → yellow.
One tube bubbles inhaled air, the other exhaled air, through limewater.
The faster colour change shows which air has more CO₂.

See the full worked example for investigating breathing in humans →

Part 1: results and conclusion

Exhaled air turns limewater milky faster, so it has more CO₂.

What you observe:

The limewater that exhaled air bubbles through goes cloudy/milky much faster (and more strongly).
The limewater for inhaled air stays clear for far longer (atmospheric air is only ~0.04% CO₂).

	Inhaled (atmospheric) air	Exhaled air
Carbon dioxide	very little (~0.04%)	much more (~4%)
Limewater	stays clear for a long time	goes milky quickly
Hydrogencarbonate indicator	stays red(dish)	turns yellow

Conclusion:

Exhaled air contains more carbon dioxide than inhaled air.
This is because the body respires, using oxygen and producing carbon dioxide as a waste product, which is then breathed out.

Skills marks examiners look for:

A valid comparison (you must compare exhaled with inhaled — not just say "exhaled air has CO₂").
Stating the result in terms of how quickly the limewater changes, not just that it changed.

Exhaled-air limewater goes milky faster → exhaled air has more CO₂.
Atmospheric air ≈ 0.04% CO₂; exhaled air ≈ 4% CO₂.
CO₂ is the waste product of respiration that we breathe out.

See the full worked example for investigating breathing in humans →

Part 2: the effect of exercise on breathing (method)

Measure breathing rate (and depth) before and after exercise.

The second investigation shows what happens to breathing when you exercise.

What to measure:

Breathing rate = the number of breaths per minute (count chest rises in 1 minute).
Breathing depth = how much air moves in/out per breath (harder to measure precisely — note "deeper/shallower" by watching how far the chest moves).

Method:

Rest for a few minutes, then count the number of breaths in 1 minute (the "before"/resting reading).
Exercise for a fixed time at a fixed intensity (e.g. step-ups or jogging on the spot for 2 minutes).
Immediately after exercise, count the breaths in 1 minute again (the "after" reading). Note whether breaths look deeper.
Repeat the whole thing several times (resting fully in between) and calculate a mean for each condition.

Controlling variables (fair test):

Use the same person throughout.
Keep the type, time and intensity of exercise the same for each repeat.
Allow the person to return to rest before any repeat.

Exam tip. Examiners reward a before vs after design with repeats and a mean, plus a stated control (same exercise, same person).

Count breaths per minute at rest, then again straight after exercise.
Keep the exercise (type, time, intensity) and the person the same.
Repeat and find a mean to improve reliability.

See the full worked example for investigating breathing in humans →

Part 2: results, conclusion and explanation

Breathing rate and depth increase; this supplies more O₂ and removes more CO₂.

Typical results:

Condition	Breaths per minute (example)	Depth
At rest	~12–15	normal
Just after exercise	~25–35	deeper

After exercise, breathing rate increases and breaths become deeper.
The values gradually return to resting as you recover.

Conclusion: exercise increases breathing rate and depth.

Explanation (the key marks):

During exercise the muscles contract more, so they respire faster (more aerobic respiration).
They need more oxygen to release the energy and they produce more carbon dioxide.
Breathing faster and deeper delivers more oxygen to the blood (and muscles) and removes the extra carbon dioxide more quickly.

Breathing rate is much higher just after exercise, then returns to resting during recovery.

Going deeper (for top marks). Breathing also stays raised for a while after stopping because the muscles must clear an oxygen debt — the extra oxygen needed to break down lactic acid built up during any anaerobic respiration.

Breathing rate and depth rise during/after exercise, then recover.
Muscles respire more → need more O₂ and make more CO₂.
Faster, deeper breathing supplies O₂ and removes CO₂ more quickly.

See the full worked example for investigating breathing in humans →

Quick recap

Limewater goes milky with CO₂; exhaled air turns it milky faster than inhaled air → exhaled air has more CO₂.
Hydrogencarbonate indicator (red → orange → yellow) is an alternative CO₂ detector.
Measure breathing rate (breaths per minute) at rest and just after exercise; repeat for a mean.
Exercise increases breathing rate and depth.
It rises because muscles respire more, needing more O₂ and producing more CO₂.

Memorise this

Verbatim phrases and definitions Edexcel mark schemes credit.

Limewater + CO₂ → cloudy/milky; faster change = more CO₂.
Exhaled air ≈ 4% CO₂; inhaled air ≈ 0.04% CO₂.
Breathing rate = breaths per minute; depth = volume per breath.
Exercise → breathing rate and depth increase.
Reason: muscles respire more → need more O₂, produce more CO₂.
Fair test: same person, same exercise, repeat → mean.

How it’s examined

Assessed on Biology Paper 1 (4WSD0/1B), 2 hours, 110 marks, untiered (Double Award has no Biology Paper 2). Practical questions ask you to describe the method, state the result and conclusion, name the CO₂ test (limewater milky / hydrogencarbonate indicator), explain why breathing increases with exercise (respiration → more O₂ needed, more CO₂ made), and identify control variables for a fair test. Data-handling marks for reading a table/graph of breaths per minute are common.

Sources: Pearson Edexcel International GCSE Science (Double Award) 4SD0 specification — Issue 4, September 2024 (valid for 2026 onwards); Pearson Edexcel International GCSE Biology 4BI1 specification — Issue 4 (shared Biology Paper 1 content); Pearson Edexcel 4SD0 / 4BI1 examiner reports 2022–2024. Last reviewed 2026-06-04.

Take this whole topic with you

Step-by-step worked examples — Investigating breathing in humans

Step-by-step solutions to past-paper-style questions on investigating breathing in humans, written exactly the way a tutor would explain them at the board.

Question type:

1Name the test for carbon dioxide (Getting started)
Getting startedIdentify & classify• 4WSD0/1B style — short answer• limewater, carbon-dioxide, spec-2.50
Question
A student bubbles exhaled air through a chemical to test for carbon dioxide. Name a suitable chemical and state what you would see if carbon dioxide is present. (2 marks)
Step-by-step solution
1. Step 1
  Chemical (1). Limewater (calcium hydroxide solution). (Hydrogencarbonate indicator is also accepted.)
2. Step 2
  Observation (1). It turns cloudy / milky (limewater); or hydrogencarbonate indicator turns from red to yellow.
Answer
Limewater; it turns cloudy/milky when carbon dioxide is bubbled through it.
Examiner tip
'Goes cloudy' or 'milky' both score. Avoid vague 'it changes' — name the colour/appearance change.
2Which air has more CO₂? (Getting started)
Getting startedIdentify & classify• 4WSD0/1B style — short answer• carbon-dioxide, exhaled-air, spec-2.50
Question
Inhaled air and exhaled air are each bubbled through limewater. The limewater for exhaled air turns milky faster. What does this tell you, and why? (2 marks)
Step-by-step solution
1. Step 1
  Conclusion (1). Exhaled air contains more carbon dioxide than inhaled air.
2. Step 2
  Reason (1). The body respires, producing carbon dioxide as a waste product, which is breathed out.
Answer
Exhaled air has more carbon dioxide than inhaled air, because the body produces CO₂ in respiration and breathes it out.
Examiner tip
The mark is for the COMPARISON (more than inhaled), not just 'exhaled air contains CO₂'.
3Design the exercise investigation (Building confidence)
Building confidenceWord problem• 4WSD0/1B style — structured• exercise, method, spec-2.50
Question
Describe a method to investigate how exercise affects a person's breathing rate. Include one way to make it a fair test. (4 marks)
Step-by-step solution
1. Step 1
  Resting reading (1). While at rest, count the number of breaths in 1 minute.
2. Step 2
  Exercise (1). Exercise for a fixed time (e.g. step-ups for 2 minutes).
3. Step 3
  After reading (1). Immediately after, count the breaths in 1 minute again.
4. Step 4
  Fair test (1). Keep the same person and the same type/time/intensity of exercise (or repeat and take a mean).
Answer
Count breaths per minute at rest; exercise for a fixed time; count breaths per minute straight after; keep the same person and same exercise, repeat and take a mean.
Examiner tip
You must give a 'before' and an 'after' reading per minute, plus one genuine control. Repeats/mean also earn the fair-test mark.
4Explain why breathing rate increases (Building confidence)
Building confidenceWord problem• 4WSD0/1B style — structured• exercise, respiration, spec-2.50
Question
A student's breathing rate rises from 14 breaths per minute at rest to 32 breaths per minute after exercise. Explain why breathing rate increases during exercise. (3 marks)
Step-by-step solution
1. Step 1
  More respiration (1). During exercise the muscles contract more and respire faster.
2. Step 2
  More oxygen needed / more CO₂ made (1). They need more oxygen to release energy and produce more carbon dioxide.
3. Step 3
  Role of faster breathing (1). Breathing faster (and deeper) supplies more O₂ and removes the extra CO₂ more quickly.
Answer
Muscles respire faster during exercise, so they need more oxygen and make more carbon dioxide; breathing faster (and deeper) supplies the extra oxygen and removes the extra carbon dioxide.
Examiner tip
Link respiration → oxygen demand / CO₂ production → faster breathing. Just saying 'the body needs more energy' is too vague for full marks.
5Interpret breathing-rate data (Stretch)
StretchGraph or diagram• 4WSD0/1B style — extended• data, graph, exercise, spec-2.50
Question
A student records breaths per minute: at rest = 15; 0–1 min after exercise = 30; 3 min after = 22; 6 min after = 15. (a) Describe what the data show. (b) Suggest why the rate at 6 minutes equals the resting rate. (4 marks)
Step-by-step solution
1. Step 1
  (a) Rise (1). Breathing rate doubles immediately after exercise (15 → 30 breaths/min).
2. Step 2
  (a) Recovery (1). It then falls back over the next few minutes (30 → 22 → 15).
3. Step 3
  (b) Recovered (1). By 6 minutes the person has stopped exercising and is back at rest.
4. Step 4
  (b) Demand met (1). The muscles are respiring at the resting rate again, so the oxygen demand / CO₂ removal is back to normal (any oxygen debt repaid).
Answer
(a) Breathing rate rises sharply (15→30) just after exercise, then gradually falls back to resting over a few minutes. (b) The person has recovered: muscles are respiring at the resting rate again, so normal breathing meets their oxygen and CO₂ needs.
Examiner tip
Quote figures from the table to gain the description marks. 'Recovery' and 'oxygen debt repaid' are credit-worthy reasons.
6Improve the limewater investigation (Stretch)
StretchMulti-step problem• 4WSD0/1B style — extended• evaluation, fair-test, limewater, spec-2.50
Question
A student bubbles inhaled and exhaled air through limewater but only times how long the exhaled-air tube takes to go milky. Give two improvements that would make the investigation more valid and reliable. (4 marks)
Step-by-step solution
1. Step 1
  Time both tubes (1) for a valid comparison (1). Time how long the inhaled-air tube takes too, so you can compare them — otherwise there is no comparison.
2. Step 2
  Standardise volumes (1). Use the same volume and concentration of limewater in both tubes so the comparison is fair.
3. Step 3
  Control breathing (1). Bubble air at the same rate / for the same time / same number of breaths through each tube.
4. Step 4
  Repeat (1). Repeat the test (or use several people) and compare to make results more reliable.
Answer
Time BOTH tubes (not just the exhaled one) so the inhaled and exhaled results can be compared; use the same volume and concentration of limewater and the same breathing rate/time for each; repeat to check reliability.
Examiner tip
The key flaw is having no comparison — examiners reward identifying that both tubes must be timed under identical conditions.

Model Answers — Investigating breathing in humans

High-scoring sample answers for investigating breathing in humans on the Pearson Edexcel IGCSE Biology Paper 1 (4WSD0/1B) paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.

Question 1
4WSD0/1B style3 marks
Describe how you could show that exhaled air contains carbon dioxide. (3 marks)
Model answer
Breathe out (exhaled air) so that it bubbles through limewater.

The limewater turns cloudy / milky.

A cloudy/milky colour change shows carbon dioxide is present in the exhaled air.
Why this scores
1 mark for using limewater, 1 for the milky/cloudy observation, 1 for linking this to CO₂. Hydrogencarbonate indicator turning yellow is an accepted alternative.
Question 2
4WSD0/1B style3 marks
(a) What is meant by 'breathing rate'? (b) State what happens to a person's breathing rate when they exercise. (3 marks)
Model answer
(a) Breathing rate is the number of breaths taken per minute (1).

(b) During exercise the breathing rate increases (1), and breaths also become deeper (1).
Why this scores
Breathing rate must be 'per minute' (a rate). Both 'increases' and 'deeper' are credit-worthy.
Question 3
4WSD0/1B style5 marks
A student wants to investigate the effect of exercise on breathing rate. Describe a suitable method and explain how the results should be made reliable. (5 marks)
Model answer
While the person is at rest, count the number of breaths in 1 minute and record it.

The person then exercises for a fixed time (e.g. step-ups or jogging on the spot for 2 minutes) at a steady intensity.

Immediately after exercising, count the breaths in 1 minute again and record it.

Keep the investigation a fair test: use the same person and the same type, time and intensity of exercise each time.

Repeat the whole procedure several times (resting fully in between) and calculate a mean breathing rate for each condition to make the results more reliable.
Why this scores
Marks for: resting reading per minute; fixed exercise; after reading per minute; a stated control; repeats + mean. The word 'reliable' is earned through repeats and a mean, not single readings.
Question 4
4WSD0/1B style6 marks
Explain why both breathing rate and breathing depth increase when a person exercises. (6 marks)
Model answer
During exercise the muscles contract more and work harder, so they respire faster (more aerobic respiration).

Faster respiration means the muscle cells need more oxygen to release the energy required for contraction.

Faster respiration also produces more carbon dioxide as a waste product, which must be removed.

Breathing faster (higher rate) and deeper (larger volume per breath) moves more air in and out of the lungs each minute.

This delivers more oxygen into the blood to be carried to the muscles.

It also removes the extra carbon dioxide from the blood more quickly, keeping the body's conditions correct.
Why this scores
Build the chain: more muscle contraction → faster respiration → more O₂ needed + more CO₂ made → faster/deeper breathing supplies O₂ and removes CO₂. Award per linked idea.
Question 5
4WSD0/1B style — extended open response7 marks
Describe a complete investigation to show that exhaled air contains more carbon dioxide than inhaled air. Include the apparatus, what you would do, the expected result and the conclusion. (7 marks)
Model answer
Apparatus:

Two tubes of limewater connected by a central mouthpiece/T-piece, arranged so that breathing in draws air through one tube (inhaled/atmospheric air) and breathing out pushes air through the other tube (exhaled air).

Method:

Breathe gently in and out through the mouthpiece for a fixed time so that inhaled air bubbles through one tube and exhaled air bubbles through the other.

Use the same volume and concentration of limewater in both tubes.

Time how long each tube takes to turn cloudy/milky.

Expected result:

The limewater that exhaled air bubbles through turns milky much faster than the inhaled-air tube, which stays clear far longer.

Conclusion:

Exhaled air contains more carbon dioxide than inhaled air, because the body respires, producing carbon dioxide that is breathed out.
Why this scores
Examiner reports award marks across apparatus (both inhaled + exhaled sampled), a fair comparison (same limewater, time both), the comparative result (exhaled milky faster), and the comparative conclusion linked to respiration.
Question 6
4WSD0/1B style — extended open response8 marks
A student measured breathing rate (breaths/min) for three people before and immediately after the same exercise. Results: Person A 14→30; Person B 16→34; Person C 13→29. (a) Describe the pattern in the results. (b) Explain the pattern. (c) Suggest one reason the increase was not exactly the same for each person. (8 marks)
Model answer
(a) Pattern:

For every person the breathing rate increased after exercise (e.g. A rose from 14 to 30 breaths/min).

The rate roughly doubled in each case, so the increase is consistent across the three people.

(b) Explanation:

During exercise the muscles respire faster, so they need more oxygen and produce more carbon dioxide.

Breathing faster (and deeper) supplies the extra oxygen to the blood and removes the extra carbon dioxide more quickly.

(c) Reason for differences:

The people differ in fitness level (a fitter person's rate may rise less), or in age, size or how hard they actually worked — so their oxygen demand and CO₂ production differ slightly.
Why this scores
(a) Use the data — state that all increased and roughly doubled. (b) Standard respiration explanation. (c) Any sensible biological variable (fitness, age, body size, effort). Marks split across the three parts.

Key Definitions and Keywords — Investigating breathing in humans

Definitions to memorise and the exact keywords mark schemes credit for investigating breathing in humans answers — sharpened from recent examiner reports for the 2026 Pearson Edexcel IGCSE Biology Paper 1 (4WSD0/1B) sitting.

Breathing (ventilation)
Examiner keyword
The movement of air into and out of the lungs, bringing in oxygen and removing carbon dioxide. (Not the same as respiration.)
Breathing rate
Examiner keyword
The number of breaths taken per minute. It increases during and after exercise.
Breathing depth
Examiner keyword
The volume of air moved in or out with each breath. Breaths become deeper during exercise.
Limewater
Examiner keyword
Calcium hydroxide solution used to test for carbon dioxide; it turns cloudy/milky when CO₂ is bubbled through it.
Hydrogencarbonate indicator
Examiner keyword
An indicator that detects carbon dioxide by changing colour: red in normal air, orange in moderate CO₂ and yellow in high CO₂.
Exhaled air
Examiner keyword
The air breathed out. It contains more carbon dioxide (≈4%) and less oxygen than inhaled air, because of respiration.
Respiration
Examiner keyword
The chemical process in cells that releases energy from glucose, using oxygen and producing carbon dioxide (in aerobic respiration). This is why exhaled air has more CO₂.
Fair test (control variables)
Keeping all variables the same except the one being tested — e.g. same person and same exercise type, time and intensity — so the comparison is valid.

Common Mistakes and Misconceptions — Investigating breathing in humans

The traps other students keep falling into on investigating breathing in humans questions — taken from recent Pearson Edexcel IGCSE Biology Paper 1 (4WSD0/1B) examiner reports and mark schemes — and how to avoid them.

✕Confusing 'breathing' with 'respiration'
Edexcel Biology examiner reports
Why it happens
Both words are used loosely in everyday English and sound similar.
How to avoid it
Breathing = moving air in and out of the lungs. Respiration = the chemical release of energy in cells. Exercise speeds up both, but they are not the same thing.
✕Saying 'exhaled air contains CO₂' without comparing to inhaled air
Edexcel Biology examiner reports 2022–2024
Why it happens
Students answer the easier 'does it contain CO₂' instead of the actual comparison question.
How to avoid it
The question is comparative: state that exhaled air has MORE CO₂ than inhaled air, and that its limewater goes milky faster.
✕Saying limewater 'changes colour' or goes a specific colour
Edexcel Biology examiner reports
Why it happens
Students confuse limewater with coloured indicators.
How to avoid it
Limewater is colourless and goes cloudy / milky / white with CO₂. Only the hydrogencarbonate indicator changes colour (red → yellow).
✕Explaining the exercise result with only 'the body needs more energy'
Edexcel Biology examiner reports
Why it happens
It feels like a complete answer but skips the biology.
How to avoid it
Link the chain: muscles respire faster → need more oxygen and make more CO₂ → so breathing rate and depth increase to supply O₂ and remove CO₂.
✕Forgetting to state a control variable / fair test
Edexcel Biology examiner reports
Why it happens
Students focus on the steps and skip making it a valid comparison.
How to avoid it
Always state at least one control: same person, and same type, time and intensity of exercise. Add repeats and a mean for reliability.
✕Giving breathing rate without 'per minute' (not a rate)
Edexcel Biology examiner reports
Why it happens
Students count breaths but forget rate needs a time unit.
How to avoid it
A rate must be per unit time — count and state breaths per minute. A bare number of breaths is not a rate.

Investigating breathing in humans

Detailed Study Notes

At a glance

What you’ll learn

Quick recap

Memorise this

How it’s examined

Take this whole topic with you

1Name the test for carbon dioxide (Getting started)

2Which air has more CO₂? (Getting started)

3Design the exercise investigation (Building confidence)

4Explain why breathing rate increases (Building confidence)

5Interpret breathing-rate data (Stretch)

6Improve the limewater investigation (Stretch)

Breathing (ventilation)

Breathing rate

Breathing depth

Limewater

Hydrogencarbonate indicator

Exhaled air

Respiration

Fair test (control variables)

✕Confusing 'breathing' with 'respiration'

✕Saying 'exhaled air contains CO₂' without comparing to inhaled air

✕Saying limewater 'changes colour' or goes a specific colour

✕Explaining the exercise result with only 'the body needs more energy'

✕Forgetting to state a control variable / fair test

✕Giving breathing rate without 'per minute' (not a rate)