Biology  by Bradford
IB Biology 2025 · Theme C · Interaction and interdependence

C1.2 Cell respiration. Practice questions with markscheme.

58 original IB-style questions on C1.2, written from the 2025 guide: 26 multiple-choice, 17 short-answer, 8 data-based, 3 extended-response part, 2 drawing, 2 labelling. Below is a 20-mark standard-level practice paper built from them, ready to hand out as a class quiz or homework, or to sit yourself and mark against the scheme. Print it, project it, or build a fresh one on the same topic.

What the guide asks for

6 statements at SL and HL, 11 additional higher level.

  1. C1.2.1SL / HL ATP as the molecule that distributes energy within cells
  2. C1.2.2SL / HL Life processes within cells that ATP supplies with energy
  3. C1.2.3SL / HL Energy transfers during interconversions between ATP and ADP
  4. C1.2.4SL / HL Cell respiration as a system for producing ATP within the cell using energy released from carbon compounds
  5. C1.2.5SL / HL Differences between anaerobic and aerobic cell respiration in humans
  6. C1.2.6SL / HL Variables affecting the rate of cell respiration
  7. C1.2.7HL Role of NAD as a carrier of hydrogen and oxidation by removal of hydrogen during cell respiration
  8. C1.2.8HL Conversion of glucose to pyruvate by stepwise reactions in glycolysis with a net yield of ATP and reduced
  9. C1.2.9HL Conversion of pyruvate to lactate as a means of regenerating NAD in anaerobic cell respiration
  10. C1.2.10HL Anaerobic cell respiration in yeast and its use in brewing and baking
  11. C1.2.11HL Oxidation and decarboxylation of pyruvate as a link reaction in aerobic cell respiration
  12. C1.2.12HL Oxidation and decarboxylation of acetyl groups in the Krebs cycle with a yield of ATP and reduced
  13. C1.2.13HL Transfer of energy by reduced NAD to the electron transport chain in the mitochondrion
  14. C1.2.14HL Generation of a proton gradient by flow of electrons along the electron transport chain
  15. C1.2.15HL Chemiosmosis and the synthesis of ATP in the mitochondrion
  16. C1.2.16HL Role of oxygen as terminal electron acceptor in aerobic cell respiration
  17. C1.2.17HL Differences between lipids and carbohydrates as respiratory substrates

In the bank for C1.2

  • 26 multiple-choice
  • 17 short-answer
  • 8 data-based
  • 3 extended-response part
  • 2 drawing
  • 2 labelling
  • 33 higher level only

Every question is original and tagged to a guide statement. See the whole bank →

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The practice paper

Take it on screen → Build a fresh paper Paper code BbB-EAAAABAAABQAOzde
Biology · topic quiz
Standard level · topic practice, not an exam format
30 minutes20 marks

Paper code: this paper was generated, so the code is its recipe. Enter it at biologybybradford.com/exam-maker to rebuild this exact paper and its markscheme.

Covers C1.2 Cell respiration
Name:
1.

Which statements about ATP are correct?
I. Hydrolysis of ATP to ADP releases energy for cell processes.
II. ATP is well suited as an energy currency because it is stable over long periods and stores energy for years.
III. ATP can be regenerated from ADP and phosphate using energy from respiration.

[1]
  1. I, II and III
  2. I and II only
  3. I and III only
  4. II and III only
2.

In a respirometer containing germinating seeds and potassium hydroxide solution, the coloured liquid in the capillary tube moves towards the seeds. What does this movement measure?

[1]
  1. The volume of carbon dioxide released, because the gas is absorbed by the potassium hydroxide and pulls the liquid along
  2. The total volume of gas exchanged, because oxygen and carbon dioxide are both absorbed by the potassium hydroxide
  3. The heat released by respiration, which expands the gas in the tube and pushes the coloured liquid outwards
  4. The volume of oxygen taken up, because the carbon dioxide released is absorbed by the potassium hydroxide
3.

Why do cells use ATP, rather than glucose directly, as their immediate source of energy?

[1]
  1. Glucose cannot cross the plasma membrane
  2. ATP stores more energy per molecule than glucose
  3. Glucose can only release energy in the presence of oxygen
  4. ATP releases energy in small, usable amounts in a single reaction
4.

Which property of ATP makes it suitable as the immediate energy currency of the cell, rather than glucose being used directly for every energy-requiring process?

[1]
  1. ATP releases a small, usable quantity of energy when a single phosphate bond is hydrolysed
  2. ATP is a much larger and more complex molecule than glucose, so it stores far more energy
  3. ATP cannot be broken down at all, so its stored energy is released only once per molecule
  4. ATP is synthesized directly from carbon dioxide and water during aerobic respiration
5.

Why is cell respiration essential in every living cell, including cells that are not growing or dividing?

[1]
  1. It produces the carbon dioxide that cells need to make carbohydrates and other organic molecules from simpler ones
  2. It supplies the oxygen that cells need to prevent the build-up of lactate and other toxic waste products
  3. It regenerates ATP, which is needed continuously for active transport, synthesis and other energy-requiring processes
  4. It breaks down proteins into amino acids so that nitrogenous waste can be excreted before it becomes toxic
6.

Outline anaerobic cell respiration in humans.

[3]
7.

Outline why cell respiration is essential in all living cells.

[2]
8.

Cells contain only a small quantity of ATP at any moment, yet use very large amounts of it each day. Outline the cycle of interconversions between ATP and ADP that makes this possible.

[3]
9.

A student investigated the effect of glucose concentration on the rate of anaerobic respiration in a yeast suspension by counting the number of carbon dioxide bubbles released per minute through a delivery tube. The results are shown in the table.

Glucose concentration / % w/vMean bubbles per minute
00
29
417
624
825
1025
(a)Describe the relationship between glucose concentration and the rate of carbon dioxide production shown in the table.[2]
(b)Explain the shape of the relationship you described in (a).[2]
(c)Identify one variable that should be controlled in this investigation.[1]
(d)State the gas being collected and name the pathway by which it is produced in this investigation.[2]

Original practice questions © Biology by Bradford · CC BY-NC-SA 4.0 · Not affiliated with or endorsed by the International Baccalaureate Organization.
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Markscheme BbB-EAAAABAAABQAOzde

One mark per point; / separates alternative wording within a point, OR separates alternative answers, words in brackets are not required, underlined words are essential. OWTTE = or words to that effect.

1. C1.2.1 [1]
  • C: ATP is an immediate, short-term energy currency, continuously recycled, not a long-term store;
2. C1.2.2 [1]
  • D: CO₂ is removed by the KOH, so the fall in gas volume equals the O₂ consumed;
3. C1.2.1 [1]
  • D: hydrolysis of ATP releases a small, manageable quantity of energy immediately; releasing all of glucose's energy at once would waste most of it (as heat);
4. C1.2.1 [1]
  • A — hydrolysis of the terminal phosphate releases a small amount of energy, suited to driving individual cellular reactions, unlike the larger, harder-to-release energy in glucose;
5. C1.2.4 [1]
  • C: ATP cannot be stored in quantity and is used constantly, so it must be regenerated continuously;
6. C1.2.5 [3 max]
  • occurs when oxygen supply is insufficient / during intense (short) exercise;
  • glucose is (partially) broken down to lactate;
  • small yield/amount of ATP (per glucose) compared with aerobic respiration;
  • occurs in the cytoplasm / no mitochondria required, OWTTE;

Do not accept lactic acid causing "muscle burn" as a marking point.

7. C1.2.4 [2 max]
  • it releases energy from carbon compounds/glucose (by oxidation);
  • the energy is transferred to ATP;
  • ATP powers cell processes, e.g. active transport / synthesis (of macromolecules) / movement;
8. C1.2.3 [3 max]
  • ADP + phosphate is converted to ATP using energy (released) from cell respiration;
  • hydrolysis of ATP to ADP + phosphate releases energy;
  • the released energy drives cell activities e.g. active transport / synthesis of macromolecules / movement;
  • each molecule is recycled many times / interconversion is continuous and rapid, so only a small pool of ATP/ADP is needed, OWTTE;
9. C1.2.6
  • (a) [2]
    • rate of CO2 production increases with glucose concentration up to about 6–8 %;
    • above about 8 % glucose concentration, the rate levels off (no further increase), OWTTE;
  • (b) [2 max]
    • at low glucose concentrations, glucose (substrate) availability limits the rate of respiration, so more glucose increases the rate;
    • at higher concentrations another factor becomes limiting, e.g. the amount/activity of respiratory enzymes (or oxygen for the aerobic component), OWTTE;
  • (c) [1]
    • temperature (accept: yeast concentration/mass, volume of suspension, time allowed);
  • (d) [2]
    • carbon dioxide;
    • produced by anaerobic respiration / alcoholic fermentation in yeast;

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