A-LevelBiologyTransport in mammals9700/12 · Feb/Mar 2016 · Q281 Mark
Cardiac muscle is made up of many fibres that form the walls of the chambers of the heart. When the heart contracts, these fibres shorten in length so the muscle creates a force that exerts a pressure on the blood, causing it to move. Which statement explains the difference in thickness of the walls of ventricles of the heart?
AThere is more muscle in the wall of the right ventricle than that of the left ventricle because more pressure is needed to push blood into the aorta than into the pulmonary artery.
BThe number of muscle fibres in the left ventricle is greater than the number in the right ventricle so their contraction has more force, exerting more pressure on blood.
CThe space available to fill with blood inside the left ventricle is smaller than that of the right ventricle so more pressure is needed to force blood out.
DThe wall of the right ventricle is thicker than that of the left ventricle because it has to resist more pressure when the muscle of the right ventricle contracts.
✓ Correct answer
B: The number of muscle fibres in the left ventricle is greater than the number in the right ventricle so their contraction has more force, exerting more pressure on blood.
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