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Date	May 2022	Marks available	3	Reference code	22M.2.HL.TZ1.5
Level	Higher level	Paper	Paper 2	Time zone	Time zone 1
Command term	Explain	Question number	5	Adapted from	N/A

Question

The diagram shows a section through part of the leg of an insect and antagonistic muscles X and Y. The tibia moves in the direction shown by the arrow when the muscle is flexing.

[Source: D G Mackean www.biology-resources.com.]

Outline a reason for the muscles being described as antagonistic.

[1]

Describe the role of muscle Y.

[2]

Outline how the muscle attachment of insects differs from humans.

[1]

Explain the role of calcium ions in muscle contraction.

[3]

Markscheme

cause opposite movements / pull in opposite directions / when one contracts the other relaxes;

flexor/flexion;
bends/flexes the leg/limb/joint;

insect muscle is attached inside (the skeleton) and human muscle outside (the skeleton);
insect muscle is attached to exoskeleton and human to endoskeleton/bones;

calcium released from sarcoplasmic reticulum;
calcium binds to troponin;
causes tropomyosin to move;
uncovers binding sites;
myosin heads bind to the actin forming cross bridges;

Examiners report

Most candidates were able to outline what antagonistic muscles are. The term 'extended' was sometimes used instead of 'relax' which is the preferred term as it indicates passivity.

The mark scheme here was rather too demanding and very few candidates were awarded both marks. The biological distinctions between flexors and flexion were too fine and marks should have been awarded for other relevant ideas. A flexor is a muscle that causes flexion. Although we may speak colloquially of 'flexing our muscles' it is not a muscle that flexes but a limb at a joint.

This question probed whether candidates understood the difference between the skeletons of mammals and insects and thus where muscles are attached. Although the diagram shows tendon-like attachment of insect muscles, many candidates claimed that the lack of tendons was the prime difference.

Well prepared candidates had no difficulty in describing the role of calcium in muscle contraction but they were in the minority. The discrimination index was very high.

Syllabus sections

Additional higher level » Topic 11: Animal physiology » 11.2 Movement

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Additional higher level » Topic 11: Animal physiology

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