| Date | November 2017 | Marks available | 4 | Reference code | 17N.3.HL.TZ0.22 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Describe | Question number | 22 | Adapted from | N/A |
Question
The micrograph shows a section of cardiac muscle.
[Source: Musculocardiaco by Goyitrina (https://commons.wikimedia.org/wiki/File:Musculocardiaco.jpg)]
Identify the structure labelled X.
Describe the unique properties of cardiac muscle cells.
State an early invention that led to improved knowledge of the heart.
Markscheme
intercalated disc
a. cells are myogenic/self-excitatory
b. cells are joined end to end
OR
cells are joined by intercalated disc
c. «intercalated discs» allow for faster propagation «of signal»
d. cells contract together for coordinated contraction
e. contain many mitochondria
f. cells are branching/Y-shaped
g. controlled by pacemaker/sinoatrial/SA and atrioventricular/AV nodes
[Max 4 Marks]
stethoscope
OR
electrocardiograph/ECG
Allow other valid example.
