Edexcel International GCSE Biology 4BI1: Gas exchange – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover sub-topic (g) Gas exchange of Topic 2 in the Pearson Edexcel International GCSE Biology (4BI1) specification, Issue 3: points 2.40B–2.50. The qualification is untiered and a calculator may be used on both papers. Questions on the flowering-plant points (2.40B–2.45B) are labelled (Paper 2 only), because those points carry a B reference; the rest can appear on either paper.

Learn the content first with the gas exchange study guide and the gas exchange revision notes. Course links: Edexcel IGCSE Biology hub and printable checklist. For other parts of Topic 2, try the cell structure practice questions.

Questions

1. State, in order, the two types of tube that air passes through between the trachea and the alveoli. [2]

2. Describe the role of the pleural membranes. [2]

3. Describe how the intercostal muscles and the diaphragm cause air to leave the lungs when a person breathes out at rest. [4]

4. Explain how two features of the alveoli and one feature of their blood supply increase the rate of gas exchange. [4]

5. Five students counted their breaths for one minute at rest and again straight after three minutes of running on the spot.

Student	A	B	C	D	E
Breaths per minute at rest	12	14	13	15	16
Breaths per minute after exercise	30	33	28	31	33

(a) Calculate the mean breathing rate at rest and after exercise. [2] (b) Calculate the percentage increase in mean breathing rate. Give your answer to 1 decimal place. [2] (c) Another student breathes 16 times per minute with 0.50 dm³ per breath at rest, and 30 times per minute with 1.8 dm³ per breath during exercise. Volume breathed per minute = breaths per minute × volume per breath. Calculate how many times greater the volume breathed per minute is during exercise. [2]

6. A student breathes in and out through a two-tube apparatus. Inhaled air is drawn through limewater in tube X; exhaled air bubbles through limewater in tube Y.

(a) State the result you would expect. [1] (b) Explain this result in terms of processes happening in the body. [2] (c) State one other difference between inhaled and exhaled air. [1]

7. (Paper 2 only) Explain how the structure of a leaf is adapted for gas exchange. [4]

8. (Paper 2 only) A student set up four sealed tubes, each containing the same volume of red hydrogen-carbonate indicator. Tubes A, B and C each held a leaf of the same size on a gauze platform. Tube D had no leaf. All four were placed 20 cm from a lamp for three hours.

• Tube A: wrapped in foil
• Tube B: covered with several layers of tissue paper
• Tube C: uncovered
• Tube D: uncovered, no leaf

(a) Predict the colour of the indicator in each tube after three hours, assuming tube B is at the light intensity where photosynthesis and respiration are equal. [4] (b) Explain the result in tube C. [2] (c) Give two variables, other than leaf size and volume of indicator, that the student should keep the same. [2]

9. (Paper 2 only) A plant releases carbon dioxide by respiration at a constant 2.0 arbitrary units per hour. At midday, photosynthesis uses carbon dioxide at 9.0 arbitrary units per hour.

(a) Calculate the net carbon dioxide uptake at midday. [1] (b) At dusk the rate of photosynthesis falls to 2.0 arbitrary units per hour. State and explain the net exchange of carbon dioxide at this time. [2] (c) State the net carbon dioxide exchange at midnight. [1]

10. The table shows data on deaths from coronary heart disease. (These figures are invented for this question.)

Group	Deaths per 100 000 people per year
Non-smokers	120
Smokers	290

(a) Calculate how many times greater the death rate is for smokers. Give your answer to 2 significant figures. [1] (b) Explain how carbon monoxide and nicotine in tobacco smoke increase the risk of a heart attack. [4] (c) Suggest why these data alone do not prove that smoking causes coronary heart disease. [1]

11. A pair of human lungs contains about 3.0 × 10⁸ alveoli. Assume each alveolus has a surface area of 2.5 × 10⁻⁷ m².

(a) Calculate the total surface area of the alveoli. [2] (b) In a person with emphysema, the surface area is 40% smaller. Calculate the new surface area. [1] (c) Explain why a person with emphysema becomes breathless during exercise. [4]

Answers

1. Bronchi [1], then bronchioles [1]. Answer: bronchi → bronchioles [2] Examiner insight: Both names must be in the right order for full credit; “bronchus tubes” without the bronchioles scores only the first mark.

2. The pleural membranes line the outside of the lungs and the inside of the thorax [1]. The fluid between them reduces friction as the lungs move during breathing [1]. [2] Examiner insight: “Protects the lungs” is too vague to score; the creditworthy idea is reducing friction.

3. External intercostal muscles relax, so the ribs move down and in [1]. The diaphragm relaxes and moves upwards into a dome [1]. The volume of the thorax decreases [1], so the pressure inside rises above atmospheric pressure and air is forced out [1]. [4] Examiner insight: Volume and pressure are separate marking points; “the lungs get smaller so air goes out” usually scores only one.

4. Many alveoli give a large surface area [1]. Alveolar walls are one cell thick, giving a short diffusion distance [1]. A dense capillary network with constant blood flow [1] keeps the concentration gradient steep [1]. [4] Examiner insight: Each feature needs its effect; listing three features with no explanation scores at most half the marks.

5. (a) Rest: (12 + 14 + 13 + 15 + 16) / 5 = 14 breaths per minute [1]. After exercise: (30 + 33 + 28 + 31 + 33) / 5 = 31 breaths per minute [1]. (b) (31 − 14) / 14 × 100 [1] = 121.4% [1]. (c) Rest: 16 × 0.50 = 8.0 dm³; exercise: 30 × 1.8 = 54 dm³ [1]. 54 / 8.0 = 6.75 times [1]. Examiner insight: In (b) dividing by the after-exercise mean is a common slip; errors carried forward from (a) are usually allowed if the method is correct.

6. (a) The limewater in tube Y turns cloudy (milky) sooner than in tube X [1]. (b) Body cells respire and produce carbon dioxide [1]; it diffuses into the blood and out into the alveoli, so exhaled air has more carbon dioxide [1]. (c) Any one: exhaled air has less oxygen, more water vapour, or is warmer [1]. Examiner insight: Writing that exhaled air “contains carbon dioxide and inhaled air does not” is wrong; both contain it, in different amounts.

7. Thin leaf, so a short diffusion distance to the cells [1]. Air spaces in the spongy mesophyll let gases reach all cells and give a large internal surface area [1]. Stomata, mostly on the lower surface, let gases diffuse in and out [1]. Moist cell walls let gases dissolve before diffusing into cells [1]. [4] Examiner insight: Points about palisade chloroplasts relate to photosynthesis, not gas exchange, and are not credited here.

8. (a) A: yellow [1]. B: red (unchanged) [1]. C: purple [1]. D: red (unchanged) [1]. (b) In bright light photosynthesis is faster than respiration [1], so carbon dioxide is removed from the air in the tube, lowering its concentration [1]. (c) Any two: temperature; time left; distance from the lamp; type or age of leaf; starting colour of indicator [1] [1]. Examiner insight: For (b) you must compare the two rates; “the leaf photosynthesises” alone does not explain why carbon dioxide falls, since respiration continues.

9. (a) 9.0 − 2.0 = 7.0 arbitrary units per hour [1]. (b) No net exchange, because photosynthesis uses carbon dioxide at the same rate that respiration releases it [1] [1]. (c) 2.0 arbitrary units per hour released (respiration only) [1]. Examiner insight: “No gas exchange” at dusk loses the explanation mark; the word “net” and the equal-rates idea are both needed.

10. (a) 290 / 120 = 2.42, so 2.4 times [1]. (b) Carbon monoxide combines with haemoglobin, so the blood carries less oxygen [1]. Nicotine raises heart rate and blood pressure [1]. Smoking increases fatty deposits that narrow the coronary arteries, which can be blocked by a clot [1]. Heart muscle then gets too little oxygen, so it cannot respire and may die [1]. (c) Other factors, such as diet, exercise or age, may differ between the groups [1]. Examiner insight: Answers must name the coronary arteries and oxygen supply to heart muscle; “blocks the heart” does not score.

11. (a) 3.0 × 10⁸ × 2.5 × 10⁻⁷ [1] = 75 m² [1]. (b) 75 × 0.60 = 45 m² [1]. (c) Alveolar walls break down, so the surface area for gas exchange is smaller [1]. Less oxygen diffuses into the blood per minute [1]. During exercise muscles need more oxygen for aerobic respiration [1], so the person breathes faster and deeper to try to make up the shortfall [1]. Examiner insight: A unit is needed in (a) and (b); in (c), link surface area to rate of diffusion rather than just saying the lungs are “damaged”.

Where marks are usually lost

• Writing the airway order wrongly, or naming the bronchioles before the bronchi.
• Describing breathing out with the muscles contracting, or leaving out the volume and pressure steps.
• Listing alveolus features without the effect on diffusion.
• Dividing by the wrong mean in percentage-change calculations.
• Saying inhaled air contains no carbon dioxide.
• Getting indicator colours the wrong way round, or saying the balanced tube had no gas exchange at all.
• Forgetting that respiration happens in the light as well as in the dark.
• Explaining heart disease without mentioning the coronary arteries.
• Treating a correlation in smoking data as proof of cause.
• Leaving units off surface-area or volume answers.

Next steps

• Recap with the gas exchange revision notes.
• Re-learn anything you missed in the gas exchange study guide.
• See the whole course on the Edexcel IGCSE Biology hub and track progress on the printable checklist.
• Try all free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

Pearson Edexcel International GCSE in Biology (4BI1) specification, Issue 3 (first teaching September 2017, first examination June 2019), published by Pearson Education Limited. Topic 2, sub-topic (g) Gas exchange, points 2.40B–2.50.