Question 19N.2.HL.TZ0.5
| Date | November 2019 | Marks available | [Maximum mark: 8] | Reference code | 19N.2.HL.TZ0.5 |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Discuss, Explain, Identify | Question number | 5 | Adapted from | N/A |
This light micrograph shows skeletal muscle.
[Source: adapted from https://en.wikipedia.org/wiki/Skeletal_muscle#/media/File:Skeletal_
muscle_%E6%A8%AA%E7%BA%B9%E8%82%8C1.JPG, Urana/ 乌拉跨氪]
Identify the dark structure indicated by I.
[1]
nucleus ✔
Identify the protein producing the thick filament in the dark band indicated by II.
[1]
myosin ✔
Identify the structure indicated by III.
[1]
muscle fibre/muscle cell ✔
Reject myofibril because it would be much narrower – diameter
Discuss whether the tissue shown in the micrograph consists of cells or not.
[2]
a. «muscle fibres are» multinucleate/contain many nuclei «whereas cells are expected to have only one/so muscle fibers are an exception to the cell theory» ✔
b. one cell membrane/sarcolemma enclosing a whole muscle fibre «as expected for cells» ✔
c. very large/much larger/longer/than most cells ✔
d. muscle fibres formed by fusion of cells/are syncytia ✔
Explain how calcium is involved in muscle contraction.
[3]
a. action potential/nerve impulse causes release of calcium ✔
b. from sarcoplasmic reticulum/specialized endoplasmic reticulum ✔
c. binds to troponin ✔
d. causes tropomyosin to move/be removed «from binding sites» ✔
e. exposes myosin-binding sites on actin/allows myosin «heads» to bind to actin ✔