State one condition which would require the use of an artificial pacemaker.

Describe briefly how an artificial pacemaker works.

The structure labelled X in the micrograph is a junction between two cardiac muscle cells. Identify the structure labelled X.

Explain how the structure of cardiac muscle cells allows propagation of stimuli through the heart wall.

a. heartbeat too slow/fast/irregular/tachycardia/fibrillations ✔ 

b. sinoatrial node is malfunctioning ✔ 

c. pathway that conducts electrical impulses generated by the sinoatrial node is impaired ✔

Do not accept heart attack

a. a pacemaker contains a battery and pulse generator
OR
it is connected to the heart by wires/cables ✔

b. it detects that the heart’s natural rhythm is incorrect ✔

c. it sends electrical impulses to correct the heartbeat/it replaces sinoatrial node ✔

d. provide a regular impulse/constant rhythm ✔

intercalated disc ✔

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 was generally well answered, with a few students identifying generic (and incorrect) medical problems such as heart attacks and hypertension.

A majority of the candidates stated that the pacemaker sends electrical impulses or replaces the SA node, and they achieved 1 mark. Few were able to state that the pacemaker is connected to the heart by wires or that it monitors the heart rate itself.

About half of the students correctly identified intercalated discs from the diagram, with the most common incorrect answer being Z-lines or another part of the sarcomere.

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.