Question 19M.3.HL.TZ1.21b.ii
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.HL.TZ1.21b.ii |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | b.ii | Adapted from | N/A |
The micrograph shows cardiac muscle.
[Source: https://commons.wikimedia.org/wiki/File:Musculocardiaco.jpg by Goyitrina,
licensed Creative Commons Attribution-Share Alike 3.0]
Explain how the structure of cardiac muscle cells allows propagation of stimuli through the heart wall.
[2]
a. branching provides larger surface area of contact between cells
OR
is branched to allow groups of cells to work together/synchronize ✔
b. intercalated disks hold cells together so they cannot separate
OR
intercalated discs allow easy transfer of electrical impulses between cells ✔
c. contain large numbers of mitochondria ✔
d. gap junctions «in intercalated discs» form channels that allow continuous flow of cytoplasm between cell ✔
For mpa, accept branching allows connection to multiple cells
This question was yet another example where students lacked the subject-specific vocabulary to achieve the marks. The majority of candidates attempting this option were unable to identify structural features of cardiac muscle cells that help in the propagation of stimuli, instead writing about striation and the myogenic nature of cardiac tissue. Those who did write about gap junctions, Y-shaped cells or intercalated discs were unable to achieve marks because they did not explain how these structures affected the function of the cells.
