Leaves of lotus and water lily are not easily wet because the leaves

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1. have surface uneven in micro-scale and water cannot come into contact with the depressed areas due to high surface tension
2. contain an oily substance
3. contain a greasy substance
4. have surface too smooth to attract water

Select the correct answer using the code given below.

1 and 3 only

3 and 4

1 and 2 only

1, 2 and 3

Answer is Right!

Answer is Wrong!

This question was previously asked in

UPSC CAPF – 2013

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The correct option is D. Leaves of lotus and water lily are not easily wet because of the combined effect described in statements 1, 2, and 3.

The ‘lotus effect’ refers to the superhydrophobicity and self-cleaning property of lotus leaves. This is primarily due to the hierarchical microscopic and nanoscopic structure on the leaf surface (statement 1) combined with the presence of hydrophobic substances like epicuticular waxes (statements 2 and 3). The surface structure creates a rough texture where water droplets sit on the tips of micro-papillae, trapping air beneath them (Cassie-Baxter state). This minimizes contact area between water and the leaf surface, amplified by the low surface energy provided by the waxes (oily/greasy substances), resulting in high contact angles and low adhesion for water droplets. Statement 4 is incorrect as smoothness generally increases wetting.

Statement 1 describes the crucial structural aspect and its physical consequence (water cannot fully contact depressed areas, leading to high surface tension effects like droplet formation). Statements 2 and 3 describe the chemical composition of the coating (waxes), which are hydrophobic (water-repelling) and are typically described as oily or greasy. Both the structure and the hydrophobic coating are essential for the lotus effect.

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