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The first heart sound, 'LUBB', which is of longer duration, is produced at the start of ventricular systole by the closure of which valves?
AAortic and pulmonary valves
BOnly the semilunar valves
CTricuspid and bicuspid valves
DOnly the aortic valve
Answer & Solution
Correct answer: C. Tricuspid and bicuspid valves
1. The heart makes two sounds, 'LUBB' first and 'DUPP' second.
2. The question asks about 'LUBB', the longer first sound at the start of ventricular systole.
3. The semilunar (aortic and pulmonary) valves close at the END of systole, making 'DUPP'.
4. Option A (aortic and pulmonary) therefore matches 'DUPP', not 'LUBB', a trap.
5. Option B (only the semilunar valves) is wrong for the same end-of-systole reason.
6. Option D (only the aortic valve) is just one semilunar valve, again the wrong sound.
7. At the start of systole the atrioventricular valves close, namely the tricuspid and bicuspid.
8. So 'LUBB' is option C.
_Source: Samacheer Kalvi (TN SCERT) Class 10 Science, Unit 14 Transportation in Plants and Circulation in Animals "Heart Sound", p.217_
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