OxfordAQA IGCSE Biology: Bioenergetics — Practice Questions (9201)

These are original questions written for Marlbridge, in the style and at the standard of the examination. They are not reproduced past-paper questions — 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]; either light or temperature must instead be 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. The leaf’s flattened shape increases surface area for light absorption and gas exchange [1] [1]. Stomata (small pores, usually on the underside) allow carbon dioxide to diffuse into the leaf and oxygen to diffuse out [1] [1]. Internal air spaces within the leaf increase the surface area available for gas exchange between cells and the atmosphere [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. Oxygen enters through breathing (inhaled into the alveoli in the lungs) [1]; it diffuses into the blood and is carried by the circulatory system to body cells [1] [1]; glucose enters via digestion (absorbed from the small intestine into the blood) and is also carried by the circulatory system to body cells [1] [1]; both oxygen and glucose are then used in respiration, which occurs in the mitochondria of cells, releasing usable 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 exam questions increasingly 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 – the qualification is linear and untiered, so it is compulsory for every candidate.