UPSC Prelims 2021 Q22: Environment & Ecology – Ecosystems & Ecology Concepts
- (a) 1 and 2
- (b) 2 and 3
- (c) 3 and 4
- (d) 1 and 4
Answer: (b) 2 and 3
Explanation
Primary Producers in Ocean Food Chains
| Organism | Trophic Level | Primary Producer? |
|---|---|---|
| 1. Copepods | Zooplankton (consumers) | NO - Small crustaceans that feed on phytoplankton. |
| 2. Cyanobacteria | Photosynthetic bacteria | YES - Perform photosynthesis; foundational marine primary producers (e.g. Prochlorococcus, Synechococcus). |
| 3. Diatoms | Photosynthetic algae | YES - Silica-shelled unicellular algae; produce ~20% of Earth's oxygen; major phytoplankton. |
| 4. Foraminifera | Zooplankton (protozoans) | NO - Shelled protozoans, mostly heterotrophic (consumers). |
Cyanobacteria and Diatoms are primary producers. Answer: (b) 2 and 3.
Answer: (b) 2 and 3.
Why each option is right or wrong
- (a) Incorrect. Copepods are zooplankton (consumers), not producers.
- (b) CORRECT. Cyanobacteria (photosynthetic bacteria) and Diatoms (silica-shelled algae) are the main marine primary producers. Diatoms alone produce ~20% of Earth's oxygen.
- (c) Incorrect. Foraminifera are shelled protozoans (consumers), not producers.
- (d) Incorrect. Both copepods and foraminifera are consumers.
Key point
Marine primary producers = Phytoplankton = Diatoms + Cyanobacteria (dinoflagellates too). Diatoms produce ~20% of Earth's O2. Copepods (zooplankton) and Foraminifera (shelled protozoans) are CONSUMERS.
Remember
Primary producers in ocean food chains are cyanobacteria (photosynthetic bacteria like Prochlorococcus) and diatoms (silica-shelled algae producing ~20% of Earth's oxygen). Copepods and Foraminifera are consumers (zooplankton). Answer: (b) 2 and 3.
Common mistakes
- Assuming all plankton are producers. Plankton = phytoplankton (producers) + zooplankton (consumers).
- Not knowing diatoms' massive contribution to global oxygen (~20%, similar to rainforests).
- Confusing foraminifera with algae. Forams are protozoans (single-celled animals), not plants.
Exam tip
Ocean primary producers: Cyanobacteria (Prochlorococcus, Synechococcus) + Diatoms + Dinoflagellates. Together = phytoplankton = base of marine food chain. Ocean acidification and warming threaten these producers.
Sources
- NCERT Class XII Biology - Chapter 14: Ecosystem
- IPCC AR6 WG-II - Chapter on Ocean and Coastal Ecosystems