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Practice · Biology · 2025 syllabus · B3.3

IB Biology B3.3 Muscle and motility: practice questions

5 exam-style questions on B3.3 Muscle and motility, HL only: 3 multiple choice, 1 data-based and 1 short answer. Each one comes with the mark scheme, a model answer and the reasoning behind every mark. Free with your email.

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B3.3-01 · Paper 1A style · multiple choice · 1 mark · HL

Why muscles work in pairs

Why are skeletal muscles arranged in antagonistic pairs? [1]

  1. Muscles exert force only when they contract, so a second muscle is needed to reverse the movement.
  2. Each muscle can both push and pull, so a pair produces twice the force of one muscle.
  3. One muscle of the pair supplies ATP to the other while it is contracting.
  4. Titin in one muscle contracts while titin in the other muscle relaxes.
Show the answer and the reasoning

Answer: A. A is correct. Muscle tissue can only pull, by shortening; it cannot push itself back to its original length. A second muscle pulling in the opposite direction is needed to reverse a movement, and as it contracts it stretches the first. B is wrong because muscles cannot push. C is wrong because each muscle fibre makes its own ATP by respiration. D misdescribes titin: titin is an elastic protein that is stretched and then recoils; it does not contract.

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The 5 questions in B3.3

  1. B3.3-01 Why muscles work in pairsPaper 1A style · multiple choice · 1 mark · HL
  2. B3.3-02 Filament overlap in a sarcomerePaper 1A style · multiple choice · 1 mark · HL
  3. B3.3-03 Structures of the hip jointPaper 1A style · multiple choice · 1 mark · HL
  4. B3.3-04 Sliding filaments and titinPaper 2 style · short answer · 8 marks · HL
  5. B3.3-05 Shoulder range of motion in athletesPaper 1B style · data-based · 10 marks · HL

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Every Biology and Chemistry question here is original, written for practice in the style of the papers set since the 2025 syllabus, with invented data. Developed independently from the International Baccalaureate Organization, which has not endorsed it. Found a mistake? Email vytis@limeadmissions.com with the question id.