Question 19M.3.SL.TZ2.18
| Date | May 2019 | Marks available | [Maximum mark: 8] | Reference code | 19M.3.SL.TZ2.18 |
| Level | SL | Paper | 3 | Time zone | TZ2 |
| Command term | Describe, Distinguish, Sketch, State | Question number | 18 | Adapted from | N/A |
Describe the structure of cardiac muscle cells.
[2]
a. cardiac muscle cells are branched ✔
b. rich in mitochondria ✔
c. rich in glycogen granules ✔
d. formed by short cylindrical cells ✔
e. contains intercalated discs ✔
f. has gap junctions ✔
g. «intercalated discs are» transverse cross-bands which represent the attachment site between adjacent cells ✔
Do not accept myogenic as it is not a structure.
The stronger candidates could describe the structure of cardiac muscle cells.
State the name of the valves that prevent blood flowing from the arteries back into the heart.
[1]
semilunar / sigmoid / pulmonary and aortic valve ✔
Most could name the semilunar valves.
The drawing shows the typical action potential waveforms with the different phases of the cardiac cycle recorded in different regions of a human heart.
[Source: J M Nerbonne and R S Kass, (2005), Physiological Reviews, 85, pages 1205 –1253 doi:10.1152/physrev.00002.2005]
Distinguish between the different phases of the cardiac cycle in the atria and in the ventricular muscle.
[2]
a. action potential of atrium precedes the ventricle
OR
the phases happen later in ventricle
OR
atrium contracts before the ventricle ✔
b. atrium has a shorter phase 2/longer phase 2 in ventricle
OR
atrium falls abruptly in phase 2/ventricle shows a plateau in phase 2 ✔
c. phase 3 is more distinct/falls more abruptly in ventricular action potential ✔
d. ventricular phase is overall longer than atrial phase ✔
Part (c) confused many candidates and they did not realise they had to refer to the graphs in their answers. Most scored one mark for stating ventricular contraction occurs after atrial contraction.
Sketch the pattern seen in a typical electrocardiogram (ECG) trace for one complete cardiac cycle, including labels of the main features.
[3]
a. sketch with the correct shape ✔
b. P, Q, R, S and T indicated ✔
c. atrial contraction/systole/depolarisation labelled ✔
d. ventricular contraction/systole/depolarisation labelled ✔
e. ventricular relaxation/diastole/repolarization labelled ✔
Correct shape should show peaks at P R and T and dips at Q and S
In part (d) the better candidates could sketch the pattern seen in a typical electrocardiogram. Some made errors in the shape or letters but could still achieve marks for showing the areas of contraction or relaxation.
