Respiration & gaseous exchange — questions and answers
5 high-yield, syllabus-aligned questions on Respiration & gaseous exchange, covering 14 individually creditable mark points. Each one shows the answer that scores full marks under our guide, which phrase earns which mark, and a common incomplete answer — so you can see the difference rather than guess at it.
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Every question and solution is reviewed by examiners versed in WAEC and JAMB, each with more than thirty years of experience.
Mark allocations are TopMarks’ own, written against the published syllabus and Chief Examiners’ reports. They are a guide to how these answers are usually credited, not an official marking scheme.
Define2 marks
Define respiration.
TopMarks model answer
Respiration is the breakdown of food substances such as glucose in living cells to release energy, which is stored as ATP.
Suggested marking guide
1Breakdown or oxidation of food in living cells
2To release energy
Why it scores
This is the single most confused definition in the syllabus. Respiration is a CHEMICAL process happening inside cells; breathing is the physical movement of air. If your definition mentions the nose, lungs or air, you have defined breathing and the examiner cannot award either mark. The two marks are for (1) breakdown of food in cells and (2) release of energy.
A common incomplete answer
“Respiration is breathing in oxygen and breathing out carbon dioxide.”
What it costs: Nothing at all. This defines breathing, not respiration. It is the error examiners see most often on this topic, and it costs the whole question every time.
Key ideas to include: breakdown / oxidation, glucose, living cells, energy, ATP.
State3 marks
State three differences between aerobic and anaerobic respiration.
TopMarks model answer
Aerobic respiration requires oxygen, while anaerobic respiration occurs without oxygen. Aerobic respiration releases much more energy per molecule of glucose than anaerobic respiration. The end products of aerobic respiration are carbon dioxide and water, whereas anaerobic respiration produces ethanol and carbon dioxide in plants, or lactic acid in animals.
Suggested marking guide
1Oxygen required versus not required
2Aerobic releases much more energy
3Different end products
Why it scores
Differences must be PAIRED — state the aerobic side and the anaerobic side of the same feature in one sentence. Writing “aerobic needs oxygen” and later “anaerobic makes lactic acid” gives the examiner two half-comparisons on different features, and half-comparisons attract half the credit.
A common incomplete answer
“Aerobic respiration uses oxygen and anaerobic respiration does not use oxygen.”
What it costs: One mark of three. It is a correct, properly paired difference — but it is only one difference, and the question asked for three.
Key ideas to include: oxygen, energy yield, end products, ethanol, lactic acid.
Explain4 marks
Explain why the alveolus is well adapted for gaseous exchange.
TopMarks model answer
The alveoli are very numerous, giving a large surface area for diffusion. Their walls are one cell thick, so the diffusion distance is very short. They are surrounded by a dense network of blood capillaries which carries the gases away and maintains a steep concentration gradient. Their inner surfaces are moist, so oxygen dissolves before it diffuses into the blood.
Suggested marking guide
1Large surface area
2Thin wall / short diffusion distance
3Rich blood supply maintaining a concentration gradient
4Moist surface so gases dissolve
Why it scores
Every adaptation mark has two halves: the FEATURE and what it is FOR. “Thin walls” alone is a description; “thin walls, so the diffusion distance is short” is an explanation, and only the explanation satisfies the command word. Four marks means four feature-plus-function pairs.
A common incomplete answer
“The alveoli are thin so gases can pass through easily.”
What it costs: One mark of four. It correctly pairs one feature with its function, but surface area, blood supply and the moist surface are all missing — three marks lost on a topic the candidate clearly knows something about.
Key ideas to include: surface area, one cell thick, diffusion distance, capillary network, concentration gradient, moist.
State2 marks
State the word equation for aerobic respiration.
TopMarks model answer
Glucose + oxygen → carbon dioxide + water + energy
Suggested marking guide
1Correct reactants
2Correct products including energy
Why it scores
The second mark is lost more often than any other on this topic, and always in the same way: the candidate writes a chemically correct equation and forgets ENERGY. Energy is the entire point of respiration. If it is not on the right-hand side, the equation describes combustion, not respiration.
A common incomplete answer
“Glucose + oxygen → carbon dioxide + water”
What it costs: One mark of two. The reactants and both products are right, but energy is missing — a whole mark thrown away on an answer that took ten seconds to write.
Key ideas to include: glucose, oxygen, carbon dioxide, water, energy.
Explain3 marks
Explain why a person breathes faster during vigorous exercise.
TopMarks model answer
During vigorous exercise the muscles contract more rapidly, so they respire faster and need more energy. This increases the demand for oxygen. Breathing rate increases so that more oxygen is supplied to the muscles and the extra carbon dioxide produced is removed quickly.
Suggested marking guide
1Muscles respire faster and need more energy
2So more oxygen is demanded
3And the extra carbon dioxide must be removed
Why it scores
The examiner is looking for a causal chain that starts at the MUSCLE, not at the lungs. Muscles work harder → they respire faster → more oxygen in, more carbon dioxide out → breathing rate rises. An answer that begins “the body needs more oxygen” has skipped the first link and usually loses that mark.
A common incomplete answer
“Because the body needs more oxygen when you run.”
What it costs: One mark of three. The oxygen demand is credited, but nothing is said about the muscles respiring faster, and nothing about removing the extra carbon dioxide.
Practise Respiration & gaseous exchange on real questions
Reading a full-mark answer is the first half. Writing one under time is the other. A free account opens exam-standard practice in Biology with the full solution on every question.