UPSC Prelims 2021 Q30: Science & Technology – Biology
- (a) 1 and 2 only
- (b) 2 and 3 only
- (c) 1 and 3 only
- (d) 1, 2 and 3
Answer: (d) 1, 2 and 3
Explanation
Symbiotic Relationships: Which Groups Participate?
| Group | Symbiotic Examples | Can Form Symbiosis? |
|---|---|---|
| 1. Cnidarians | Corals + zooxanthellae (Symbiodinium algae); sea anemones + clownfish | YES |
| 2. Fungi | Lichens (fungus + alga); Mycorrhiza (fungi + plant roots) | YES |
| 3. Protozoa | Termite gut protozoa (Trichonympha) digests cellulose; Zooxanthellae (Symbiodinium is a dinoflagellate) | YES |
All three groups can form symbiotic relationships. Answer: (d).
Symbiosis takes many forms: mutualism (both benefit), commensalism (one benefits), parasitism (one benefits, one harmed).
Answer: (d) 1, 2 and 3.
Why each option is right or wrong
- (a) Incorrect. Protozoa also form symbioses - classic example is termite gut protozoa that digest cellulose.
- (b) Incorrect. Cnidarians (corals with zooxanthellae) are among the most famous symbiotic organisms.
- (c) Incorrect. Fungi form symbioses in lichens and mycorrhizae - foundational examples.
- (d) CORRECT. All three - Cnidarians (corals+zooxanthellae), Fungi (lichens, mycorrhizae) and Protozoa (termite gut, zooxanthellae) - form symbiotic relationships.
Key point
Symbiosis examples: Cnidarians (coral+zooxanthellae), Fungi (lichens+mycorrhiza), Protozoa (termite gut). All three groups form symbioses. Zooxanthellae are dinoflagellate protozoans living inside coral tissues.
Remember
Cnidarians (corals with zooxanthellae), Fungi (lichens and mycorrhiza) and Protozoa (termite gut Trichonympha, zooxanthellae) all form symbiotic relationships. All three groups can establish symbiosis. Answer: (d) 1, 2 and 3.
Common mistakes
- Assuming symbiosis is rare. It is one of the most common life strategies - lichens, corals, mycorrhizae, gut microbes are all examples.
- Not knowing coral bleaching is loss of symbiotic zooxanthellae from stressed corals (temperature rise).
- Confusing symbiosis with parasitism. Symbiosis is a broad term; mutualism (both benefit) is the specific mutually beneficial subset.
Exam tip
Landmark symbioses: Coral-Zooxanthellae (marine), Lichens (fungi+algae, pioneer species), Mycorrhiza (~80% of land plants), Rhizobium-legume (N-fixation), Termite gut microbes. Symbiosis powers the biosphere - understand it for both biology and ecology questions.
Sources
- NCERT Class XI Biology - Chapter 4: Animal Kingdom
- NCERT Class XII Biology - Chapter 13: Organisms and Populations