UPSC Prelims 2013 Q94: Environment & Ecology – Ecosystems & Ecology Concepts
Which of the following leaf modifications occurs/occur in desert areas to inhibit water loss?
1. Hard and waxy leaves
2. Tiny leaves or no leaves
3. Thorns instead of leaves
Select the correct answer using the codes given below.
- (a) 1 and 2 only
- (b) 2 only
- (c) 1 and 3 only
- (d) 1, 2 and 3
Answer: (d) 1, 2 and 3
Explanation
Leaf modifications of desert plants
Desert plants (xerophytes) must save water.
Most water is lost from leaves, through transpiration.
| Modification | Occurs in desert plants? | How it saves water |
|---|---|---|
| 1. Hard and waxy leaves | Yes | A thick cuticle seals in water |
| 2. Tiny leaves or no leaves | Yes | Less surface area to lose water from |
| 3. Thorns instead of leaves | Yes | Spines lose almost no water and keep animals away |
Other adaptations of xerophytes:
| Adaptation | Example |
|---|---|
| Fleshy stem that stores water | Cactus |
| Green stem does photosynthesis | Opuntia |
| Sunken stomata | Fewer openings, hidden in pits |
| Stomata open at night | CAM plants |
| Deep or widely spread roots | Reach scarce water |
Answer: (d) 1, 2 and 3.
Why each option is right or wrong
- (a) Incorrect. Thorns instead of leaves are also a desert adaptation.
- (b) Incorrect. Hard, waxy leaves and thorns are also adaptations.
- (c) Incorrect. Tiny leaves or no leaves are also an adaptation.
- (d) CORRECT. All three leaf modifications help desert plants save water.
Key point
Xerophytes: waxy cuticle, reduced or absent leaves, spines, sunken stomata, CAM photosynthesis, water-storing stems, deep roots.
Remember
Desert plants: waxy, tiny or spiny leaves.
Common mistakes
- Thinking thorns are only for defence; they also cut water loss.
- Forgetting that in a cactus the stem does the photosynthesis.
- Not knowing the term xerophyte.
Exam tip
Less leaf = less water lost. Every desert adaptation follows from this.
Sources
- NCERT Class XII — Biology (Organisms and Populations: adaptations)
- NCERT Class VII — Science (Weather, Climate and Adaptations of Animals and Plants)