This set covers five skills: explaining ventilation, linking alveolar structure to diffusion, separating gas exchange from respiration, comparing aerobic and anaerobic models, and handling respirometer data. The questions go from easier to harder, so work through them in order.
Write a full answer for each one before you open the working. All data are invented for practice.
Questions
Q1. State what the diaphragm does during inhalation.
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The diaphragm contracts and flattens, moving downwards. This increases the volume of the thorax.
Q2. Explain why air flows into the lungs when the thorax volume increases.
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When the volume increases, the pressure inside the thorax falls below atmospheric pressure. Air moves from the higher pressure outside to the lower pressure inside, so it flows in through the airways.
Q3. Name each process described: (a) air moves through the trachea into the lungs; (b) oxygen diffuses from an alveolus into a capillary; (c) glucose is broken down in a muscle cell to release energy.
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(a) Breathing (ventilation). (b) Gas exchange, by diffusion. (c) Respiration.
Q4. Give two features of the alveoli and explain how each speeds up gas exchange.
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Any two of these. The walls are one cell thick, so the diffusion distance is short. There are very many alveoli, so the total surface area is large. A dense capillary network carries gases away, so the concentration gradient stays steep. The lining is moist, so gases can dissolve before diffusing.
Q5. A model alveolar surface has an area of 50 units, a concentration difference of 30 units and a wall thickness of 0.5 units. Using the rate index = area × difference ÷ thickness, find the index. Then find it if the thickness doubles to 1.0.
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First: 50 × 30 = 1500, then 1500 ÷ 0.5 = 3000. After doubling the thickness: 1500 ÷ 1.0 = 1500. The index halves, because a thicker wall means a longer distance for diffusion.
Q6. Explain how breathing and blood flow each help to keep oxygen diffusing into the blood.
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Breathing brings fresh air with a high oxygen concentration into the alveolus. Blood flow carries oxygen away, so the oxygen concentration in the capillary stays low. Both keep the concentration gradient steep, so oxygen continues to diffuse in.
Q7. Write word equations for (a) aerobic respiration, (b) anaerobic respiration in muscle and (c) anaerobic respiration in yeast.
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(a) glucose + oxygen → carbon dioxide + water (+ energy released). (b) glucose → lactic acid (+ energy released). (c) glucose → ethanol + carbon dioxide (+ energy released).
Q8. A student sprints for 10 seconds and then walks. Explain why muscle cells use anaerobic respiration during the sprint, and why breathing stays fast afterwards.
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In the sprint the muscles need energy very fast and the oxygen supply cannot keep up, so some respiration is anaerobic and forms lactic acid. Afterwards the breathing stays fast to take in extra oxygen, which helps break down the lactic acid.
Q9. In a respirometer the coloured liquid moved 30 mm in 15 minutes. The capillary bore has a cross-sectional area of 0.5 mm². Calculate the rate of oxygen uptake in mm³ per minute.
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Rate of movement: 30 ÷ 15 = 2 mm/min. Volume rate: 2 × 0.5 = 1.0 mm³/min. Check the other way: volume taken up is 30 × 0.5 = 15 mm³, and 15 ÷ 15 = 1.0 mm³/min.
Q10. A student writes: “Respiration happens in the lungs when we breathe in, and it makes energy.” Find and correct two errors.
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First error: respiration does not happen in the lungs. Breathing and gas exchange happen there, and respiration happens in cells. Second error: respiration does not make energy. It releases energy stored in glucose.
If you got these wrong
- Q1 to Q2 wrong: return to explaining ventilation using pressure and volume. Practise writing the full chain from muscle to air flow.
- Q4 to Q6 wrong: revisit connecting alveolar structure with diffusion, and check you name the factor and its effect.
- Q3 or Q10 wrong: go to distinguishing gas exchange from respiration and name the process in every sentence.
- Q7 or Q8 wrong: study comparing aerobic and anaerobic models and rebuild the three-row equation table.
- Q9 wrong: practise with interpreting a respiration experiment from supplied data, especially the rate and area steps.
Record each slip in the mistake log and retest queue and try a fresh question on the same skill a few days later. The module overview shows the study order.
If one type of error keeps returning, the quickest route is often a teacher who reads your written answer with you. That is what we do in online one-to-one Biology tuition.