OxfordAQA IGCSE Biology: Bioenergetics — Practice Questions (9201)

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 available free from your board.

Related: Bioenergetics study guide

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Section A

1. Write the word equation for photosynthesis. [2]

2. Name the three digestive enzymes referred to in this topic and state what each breaks down. [3]

Section B

3. A greenhouse grower increases the carbon dioxide concentration around a crop, but observes no increase in growth rate. Suggest one possible explanation, referring to limiting factors. [3]

4. Explain how the structure of a leaf is adapted for efficient gas exchange during photosynthesis. [5]

5. Explain the difference between the direction of transport in xylem and phloem. [4]

6. Describe how oxygen and glucose travel from the point they enter/are absorbed by the body to the point they are used in respiration, naming the systems involved in order. [6]

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Answers

1. Carbon dioxide + water → (light) → glucose + oxygen [1] [1] (1 mark for correct reactants and products, 1 mark for indicating light is required).

2. Amylase — breaks down starch (into sugars) [1]. Protease — breaks down proteins (into amino acids) [1]. Lipase — breaks down fats/lipids (into fatty acids and glycerol) [1].

3. If growth rate does not increase despite more carbon dioxide being available, carbon dioxide was not the limiting factor in this case [1]; another factor, for example light intensity or temperature, is limiting the rate of photosynthesis [1], and increasing carbon dioxide further will not raise growth until whichever factor actually is limiting is addressed [1].

4. Any five of the following, 1 mark each [5]:

• The leaf is broad and flat, giving a large surface area for gas exchange (and light absorption) [1].
• The leaf is thin, so gases have a short diffusion distance to and from the cells [1].
• Stomata (small pores, mostly on the lower surface) let carbon dioxide diffuse into the leaf and oxygen diffuse out [1].
• Guard cells open and close the stomata, controlling gas exchange (and water loss) [1].
• Air spaces in the spongy mesophyll give a large internal surface area and let gases diffuse quickly between the stomata and the cells [1].
• The concentration gradient of carbon dioxide is kept steep because photosynthesising cells use it up [1].

5. Xylem transports water and dissolved minerals in one direction only — from the roots up to the leaves [1] [1]. Phloem transports dissolved sugars (translocation) in both directions, depending on where sugars are being produced and where they are needed for growth or storage [1] [1].

6. Any six of the following, 1 mark each [6]:

• Oxygen enters through breathing: air is inhaled into the alveoli of the lungs [1].
• Oxygen diffuses from the alveoli into the blood in the surrounding capillaries [1].
• Oxygen is carried by red blood cells (bound to haemoglobin) [1].
• Glucose comes from digestion of carbohydrates and is absorbed from the small intestine (villi) into the blood [1].
• Glucose is carried dissolved in the plasma [1].
• The circulatory system (the heart pumping blood through arteries to capillaries) delivers both to body cells [1].
• Both diffuse from the capillaries into cells, where they are used in aerobic respiration in the mitochondria, releasing energy [1].

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Exam technique for this topic

Limiting-factor questions like Q3 are testing whether you can identify which specific factor (light, temperature or carbon dioxide) is constraining growth in the scenario described, not simply recall that all three factors exist — always reason from what the scenario tells you has and has not changed, as modelled in the answer above, rather than listing all three factors generically. For questions asking you to trace a substance’s path through the body (like Q6), name each system in the correct order and state what happens at each stage, since marks are typically awarded per correctly sequenced and explained stage, not just for naming the systems involved. When distinguishing xylem from phloem, always specify direction explicitly — xylem is one-directional (roots to leaves), while phloem’s direction depends on where sugars are currently being produced versus needed — since a description of either transport system without stating direction usually only earns partial credit.

Worked example: linking limiting factors to a graph

A related question style presents a graph of photosynthesis rate against light intensity that levels off at high light intensity, and asks why the rate stops increasing. The correct reasoning follows the same principle as Q3: while light intensity is low, it is the limiting factor, so raising it increases the rate of photosynthesis in a roughly straight line [1]. Once the graph levels off (the plateau), light is no longer what is holding the rate back — some other factor, either carbon dioxide concentration or temperature, has now become limiting instead [1]. To identify which one, look for any other information given in the question: if temperature is stated as constant and controlled, carbon dioxide concentration is usually the factor now limiting the plateaued rate [1]. This graph-reading skill and the written explanation in Q3 are two forms of exactly the same underlying idea — that at any moment, only one factor is actually constraining the rate, and identifying which one requires looking at what the specific conditions in the question do and do not allow to change.

Connecting this topic to plant and human systems together

Bioenergetics deliberately spans both plant processes (photosynthesis, transport in xylem and phloem) and human processes (digestion, breathing, circulation, respiration), and questions can draw connections across both halves — for example, asking how a plant’s structure supports the gas exchange that photosynthesis depends on, then asking how the human body’s own gas exchange (breathing) and transport (circulation) systems supply oxygen for respiration in animal cells, as in Q6. Revising this topic side by side, rather than treating “plants” and “humans” as unconnected sub-topics, makes it easier to answer synoptic questions that expect a candidate to compare or link the two systems directly.

Where marks are usually lost

• Writing the respiration equation when a question asks about photosynthesis, or vice versa — always check which gas is being taken in before answering.
• Naming an enzyme without stating what substance it breaks down.
• Describing xylem or phloem without specifying the direction of transport.
• Treating B-marked content (e.g. pacemakers, stents, artificial hearts) as optional – in the specification, B marks content that is in International GCSE Biology but not in Combined Science, so it is required for every 9201 Biology candidate.