CAPF AC 2021 Q104: Geography – Oceanography
- (a) 1, 3 and 4 only
- (b) 2, 3 and 4 only
- (c) 1 and 2 only
- (d) 1, 2, 3 and 4
Answer: (b) 2, 3 and 4 only
Explanation
Conditions for the growth of corals
How to think: coral polyps are sea animals that live with tiny algae called zooxanthellae.
The algae need sunlight, so the water must be clear and shallow.
Corals die in fresh water.
| Statement | Needed? | Reason |
|---|---|---|
| 1. Freshwater | No | Corals need salt water; they are absent near river mouths |
| 2. Clear shallow salt water | Yes | Mud chokes the polyps; depth is usually under 50 to 60 metres |
| 3. Plenty of sunlight | Yes | The algae inside the coral make food by photosynthesis |
| 4. Warm water | Yes | Corals grow best in warm tropical seas |
So the correct factors are 2, 3 and 4.
Coral reefs of India: Lakshadweep (atolls), Andaman and Nicobar Islands, Gulf of Mannar and Gulf of Kachchh.
Answer: (b) 2, 3 and 4 only.
Why each option is right or wrong
- (a) Incorrect. It includes 1; fresh water kills corals.
- (b) CORRECT. Corals need clear shallow salt water, sunlight and warmth.
- (c) Incorrect. It includes fresh water and leaves out sunlight and warmth.
- (d) Incorrect. Statement 1 is wrong, so all four cannot be right.
Key point
Corals: warm tropical seas (roughly 20 to 30 °C), clear and shallow salt water, sunlight, no silt and no fresh water. Types of reef: fringing, barrier, atoll. Warming seas cause coral bleaching.
Remember
Corals: warm, clear, shallow, salty, sunlit water.
Common mistakes
- Ticking fresh water; corals are never found near large river mouths.
- Forgetting that corals need sunlight because of the algae living in them.
- Thinking corals are plants or rocks; they are tiny animals (polyps).
Exam tip
Educated guess: statement 1 says freshwater and statement 2 says salt water. They cannot both be right, so drop every option that has 1.
Sources
- NCERT Class XI Geography — Fundamentals of Physical Geography (oceans; coral reefs) and India: Physical Environment (islands)
- G. C. Leong, Certificate Physical and Human Geography — Islands and Coral Reefs