Question 23M.3.HL.TZ1.22
| Date | May 2023 | Marks available | [Maximum mark: 7] | Reference code | 23M.3.HL.TZ1.22 |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Calculate, Describe, Explain, State | Question number | 22 | Adapted from | N/A |
The diagram indicates the condition of the heart chambers during a heart cycle of duration 0.8 s, beginning with atrial systole.
[Source: Ivan Shun Ho, 2011. Visualizing the Cardiac Cycle: A Useful Tool to Promote Student Understanding. Journal of Microbiology
& Biology Education [e-journal], 12(1). https://doi.org/10.1128/jmbe.v12i1.261. Reproduced with permission from American
Society for Microbiology.]
Calculate how long all the heart chambers are in diastole at the same time.
[1]
0.4 s;
Almost all candidates could correctly determine the time in diastole from the diagram provided.
State the letter on an ECG corresponding with the events from 0.0 to 0.1 s.
[1]
P;
Candidates either knew that the letter P corresponded to the first part of an ECG or did not.
Describe the state of the heart valves at 0.3 s.
[2]
- atrioventricular/AV valves closed;
- semi-lunar valves open;
Many could correctly indicate which heart valves were open and closed at the time in the cardiac cycle indicated.
Explain how cardiac muscle is adapted to its function.
[3]
- many mitochondria for aerobic respiration;
- cells are branched allowing for faster transmission/allow impulse to spread;
- cardiac muscle is myogenic so does not require the CNS to initiate contraction;
- cells are not fused together/are connected by gap junctions/intercalated discs (which) allows easier transmission between cells;
This question was answered well by stronger candidates. Weaker candidates often simply stated something general about skeletal muscle or muscle contraction.