27 exam-style questions on Muscle and motility — topic B3.3 of Form and function in the IB Biology syllabus — with answers and explanations. Samples below; the full set is free with an account.
According to the sliding filament model, determine what happens to the sarcomere bands during muscle contraction.
Answer: The I band and H zone shorten; A band constant
During contraction the filaments slide but do not shorten, so the A band (length of thick filaments) is constant, while the I band and H zone shorten as overlap increases.
Explain the immediate role of ATP binding to the myosin head during the cross-bridge cycle.
Answer: It causes the myosin head to detach from actin
ATP binding to the myosin head causes it to detach from actin; its subsequent hydrolysis then re-cocks the head ready for the next power stroke.
Determine how calcium ions initiate contraction after an action potential reaches the sarcoplasmic reticulum.
Answer: Ca²⁺ binds troponin, moving tropomyosin aside
Released Ca²⁺ binds troponin, changing its shape so tropomyosin shifts and uncovers the myosin-binding sites on actin, allowing cross-bridges to form.
Suggest why skeletal muscles must be arranged in antagonistic pairs, such as the biceps and triceps.
Answer: Muscles pull, not push, so pairs are needed
Muscles exert force only by contracting (pulling); an antagonistic partner is required to move the bone in the opposite direction and restore the original position.
State the function of the neurotransmitter acetylcholine at the neuromuscular junction.
Answer: It depolarises the sarcolemma, triggering an action potential
Acetylcholine released from the motor neuron binds receptors on the sarcolemma, causing depolarisation that spreads down T-tubules and triggers Ca²⁺ release.
Distinguish the role of the enzyme acetylcholinesterase at the neuromuscular junction.
Answer: It breaks down acetylcholine to end stimulation
Acetylcholinesterase hydrolyses acetylcholine in the cleft, stopping continuous stimulation so the muscle can relax between impulses.
That was 6 of 27 Muscle and motility questions.
Practise all 27 freeStateAO1 · 1–2 marks
One word or one short sentence. No explanation, no working: the mark is for the fact itself.
ExplainAO3 · 3–8 marks
Give reasons or causes: say what happens AND why, linking each step with 'because' or 'so that'.
DetermineAO3 · 3–8 marks
Obtain the only possible answer — by calculation, from the graph or by reasoning — and show how.
27 Muscle and motility questions — free with an account. Spaced repetition, streaks and full exam simulations included.
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