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Transport in Mammals: Question 10

Syllabus 8.3

Multiple choice AS 1 mark

In a mammalian heart, the muscular wall of the left ventricle is considerably thicker than the muscular wall of the right ventricle, and a muscular septum completely separates the left and right sides of the heart.

Which statement best explains the functional significance of these two features?

Choose an answer to check it, then compare with the worked solution below.
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Worked solution

Step 1: Recall the two circuits each ventricle serves

The right ventricle pumps deoxygenated blood only as far as the lungs (the pulmonary circulation), a relatively short distance through vessels that offer low resistance. The left ventricle pumps oxygenated blood all the way around the rest of the body (the systemic circulation), a much longer path through vessels that offer far greater resistance.

Step 2: Recall what wall thickness and the septum actually do

Because the left ventricle must generate enough pressure to drive blood all the way around the systemic circulation, its muscular wall is considerably thicker and more powerful than that of the right ventricle, which only needs to generate enough pressure for the short pulmonary circuit. The septum is a solid muscular wall running down the middle of the heart, and it completely separates the left and right sides. This keeps oxygenated blood (in the left atrium and left ventricle) from mixing with deoxygenated blood (in the right atrium and right ventricle), which is essential for the double circulation to work efficiently. Mixing would reduce the oxygen-carrying capacity of blood sent to the body.

Step 3: Evaluate each option

  • A: correct, this matches both the pressure requirement of the systemic circulation and the separating role of the septum described above.
  • B: incorrect. It is the right ventricle, not the left, that pumps to the lungs, and it does not need a thick wall for this short, low-resistance journey; the septum does not permit mixing of blood.
  • C: incorrect, both ventricles contract together as part of the same heartbeat, at the same rate; it is the pressure each ventricle must generate, not its rate of contraction, that differs. Preventing backflow into the atria is the role of the atrioventricular valves, not the septum.
  • D: incorrect. Heart wall muscle does not store oxygen for later release, and the septum’s role is separation of the two sides of the heart, not attachment of the chordae tendineae (which attach instead to the atrioventricular valve cusps and the ventricle wall itself).

Final answer

  • The left ventricle’s thicker wall generates the higher pressure needed for the systemic circulation, and the septum keeps oxygenated and deoxygenated blood separate, option A.