UPSC Prelims 2011 Q22: Environment & Ecology – Ecosystems & Ecology Concepts
In the context of ecosystem productivity, marine upwelling zones are important as they
increase the marine productivity by bringing the
1. Decomposer microorganisms to the surface,
2. Nutrients to the surface,
3. Bottom - dwelling organisms to the surface.
Which of the statements given above is/are correct?
- (a) 1 and 2
- (b) 2 only
- (c) 2 and 3
- (d) 3 only
Answer: (b) 2 only
Explanation
Why marine upwelling boosts productivity
Upwelling is the rise of deep, cold ocean water to the surface, usually driven by wind pushing surface water away.
| Statement | Verdict | Reason |
|---|---|---|
| 1. Decomposer microorganisms brought to the surface | Incorrect | Upwelling brings nutrients, not specifically decomposer microbes, to the surface |
| 2. Nutrients brought to the surface | Correct | Deep water is rich in nitrates and phosphates that sank from decaying organic matter; bringing them to sunlit surface waters fuels phytoplankton blooms |
| 3. Bottom-dwelling organisms brought to the surface | Incorrect | Upwelling moves water, not whole bottom-dwelling organisms, to the surface |
Why this matters:
| Effect | Example |
|---|---|
| Phytoplankton bloom | Base of the marine food chain expands |
| Fisheries | Upwelling zones (e.g. off Peru, California) are among the world's richest fishing grounds |
Answer: (b) 2 only.
Why each option is right or wrong
- (a) Incorrect. Statement 1 is false; it is nutrients, not decomposer microbes, that upwelling brings up.
- (b) CORRECT. Nutrients rising to the surface is what drives higher productivity in upwelling zones.
- (c) Incorrect. Statement 3 is false; upwelling does not carry bottom-dwelling organisms to the surface.
- (d) Incorrect. Statement 3 alone is wrong; statement 2 is the correct mechanism.
Key point
Upwelling raises nutrient-rich deep water to the sunlit surface, fuelling phytoplankton growth and high productivity — not decomposer microbes or bottom-dwelling organisms.
Remember
Upwelling: nutrients rise, phytoplankton bloom, productivity rises.
Common mistakes
- Confusing nutrients (dissolved chemicals) with living decomposer microbes.
- Imagining bottom-dwelling animals physically rising with the water.
- Missing that upwelling's value is purely about nutrient supply to phytoplankton.
Exam tip
Upwelling = nutrients up, not organisms up. Any option about living creatures rising is a distractor.
Sources
- National Oceanic and Atmospheric Administration — What is upwelling?
- NCERT Class XII — Biology, Ch 14 (Ecosystem productivity)