Question 22M.2.HL.TZ1.5
| Date | May 2022 | Marks available | [Maximum mark: 7] | Reference code | 22M.2.HL.TZ1.5 |
| Level | HL | Paper | 2 | Time zone | TZ1 |
| Command term | Describe, Explain, Outline | Question number | 5 | Adapted from | N/A |
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]
cause opposite movements / pull in opposite directions / when one contracts the other relaxes;
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.
Describe the role of muscle Y.
[2]
- flexor/flexion;
- bends/flexes the leg/limb/joint;
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.
Outline how the muscle attachment of insects differs from humans.
[1]
insect muscle is attached inside (the skeleton) and human muscle outside (the skeleton);
insect muscle is attached to exoskeleton and human to endoskeleton/bones;
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.
Explain the role of calcium ions in muscle contraction.
[3]
- 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;
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.