UPSC Prelims 1999·GS1·science-and-technology·science and technology

For which one of the following is capillarity not the only reason?

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Last updated 23 May 2026, 3:31 pm IST
  1. ABlotting of ink
  2. BRising of underground water
  3. CSpread of water drop on a cotton cloth
  4. DRising of water from the roots of a plant to its foliageCorrect

Explanation

The correct answer is D because while capillarity plays a small role in the movement of water in plants, it is not the primary or only reason. The main mechanism responsible for the ascent of sap from the roots to the leaves is transpiration pull, supported by cohesion and adhesion of water molecules. Capillary action alone can only lift water to a very small height, which is insufficient for tall trees. In contrast, options A, B, and C rely almost entirely on capillary action. Blotting paper absorbs ink through tiny pores acting as capillaries, underground water rises through narrow soil spaces, and water spreads on cotton cloth because the spaces between cotton fibers act as capillary tubes.
science-and-technology: For which one of the following is capillarity not the only reason?
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