UPSC Prelims 2013 · GS Paper I
Question 50: Science and Technology
Consider the following minerals :
- 1.Calcium
- 2.Iron
- 3.Sodium
Which of the minerals given above is/are required by human body for the contraction of muscles?
AnswerUPSC’s answer is (d).
Calcium is needed for muscle contraction: calcium ions released inside the muscle fibre let the actin and myosin filaments slide past each other. Sodium helps carry the nerve impulse that triggers contraction and keeps the electrical balance of muscle cells. Iron is part of myoglobin and haemoglobin, which supply the oxygen muscles need to keep contracting. UPSC counts all three.
- 1. Calcium ions trigger the sliding of muscle filaments.
- 2. Iron in myoglobin supplies oxygen to working muscle.
- 3. Sodium is needed for the nerve impulse and for muscle cell excitation.
How you could have got this
- If you were sure statement 1 is correct, (b) goes: it leaves 1 out.
What you needed to know: Calcium ions trigger the sliding of muscle filaments.
- Then, if you were sure statement 2 is correct, (a) and (c) go: each of them leaves 2 out.
What you needed to know: Iron in myoglobin supplies oxygen to working muscle.
Only (d) is left. You didn’t need statement 3.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Wrong. Sodium and iron are also counted.
- (b) Wrong. Calcium is the central mineral for contraction and is left out.
- (c) Wrong. UPSC also counts iron.
- (d) Correct. Calcium, iron and sodium are all required for muscle function.
Worth knowing: Iron serves muscle only indirectly, through oxygen supply, so the key is arguable; UPSC counted all three.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2013, General Studies Paper I, Series A. The paper on upsc.gov.in.