Question 23 from UPSC CSE 2018 - Environment

Question

Which of the following leaf modifications occur(s) in the desert areas to inhibit water loss?
1. Hard and waxy leaves
2. Tiny leaves
3. Thorns instead of leaves
Select the correct answer using the code given below:

IASCODEX · Accepted Answer

Correct Option: D. 1, 2, and 3

Strategy: Focus on identifying adaptations that reduce water loss under arid conditions. Hard and waxy leaves, tiny leaves, and thorns are all classic modifications in desert plants to minimize transpiration. Each option represents a proven xerophytic trait, so all three statements are correct.

Key Info: Desert plants, or xerophytes, are specially adapted to survive arid conditions with extremely low precipitation. Their morphological and anatomical modifications include:

*   **Hard and Waxy Leaves**: The presence of a thick, waxy cuticle limits evaporation by forming a water-impermeable barrier. Cuticle layers are especially prominent in species like Agave and Aloe, reducing cuticular transpiration.
*   **Tiny Leaves**: Reduction in leaf size drastically lowers the surface area for transpiration. Some desert plants (e.g., Prosopis, Acacia) produce very small leaves or phyllodes.
*   **Thorns Instead of Leaves**: In many cacti and some Euphorbias, leaves are transformed into sharp thorns or spines. These structures are non-photosynthetic, preventing water loss while also deterring herbivores. Photosynthesis shifts to the stem, which is often succulent and green.
*   **Additional xerophytic adaptations** include sunken stomata (reducing water vapor loss), rolled or hairy leaves, fleshy tissues for water storage, extensive root systems for rapid water uptake, and sometimes CAM (Crassulacean Acid Metabolism) photosynthesis--opening stomata at night instead of day. All modifications aim at maximizing water utilization and minimizing loss.
*   **Examples of xerophytic plants** include cacti (e.g., Opuntia), succulents (Aloe, Agave), Euphorbia, and many plants from the Indian Thar Desert.

IASCODEX · Answer

Option A: 2 and 3 only

IASCODEX · Answer

Option B: 2 only

IASCODEX · Answer

Option C: 3 only

Which of the following leaf modifications occur(s) in the desert areas to inhibit water loss? Hard and waxy leaves Tiny leaves Thorns instead of leaves Select the correct answer using the code given below:

Which of the following leaf modifications occur(s) in the desert areas to inhibit water loss?

Hard and waxy leaves

Tiny leaves

Thorns instead of leaves
Select the correct answer using the code given below: