UPSC Prelims 2021 Q20: Environment & Ecology – Ecosystems & Ecology Concepts
- (a) 1 and 4 only
- (b) 2 only
- (c) 2 and 3
- (d) 1, 3 and 4
Answer: (c) 2 and 3
Explanation
Surviving Without Soil: Pioneer Species
| Organism | Needs Soil? | Explanation |
|---|---|---|
| 1. Fern | Yes | Ferns need moist soil with organic matter for roots and rhizoids. |
| 2. Lichen | NO | Lichens are the classic pioneer species - symbiosis of fungus + alga/cyanobacterium. Grow on bare rocks, tree bark, arctic surfaces. Secrete acids that eventually break rock into soil. |
| 3. Moss | NO | Mosses (non-vascular plants) can grow on bare rock, walls, tree bark using rhizoids (root-like structures). They need moisture but NOT soil. |
| 4. Mushroom | Yes | Mushrooms (fruiting bodies of fungi) need organic substrate (soil, wood, decaying matter) for the underlying mycelium. |
Only Lichen (2) and Moss (3) can survive on soilless surfaces. Answer: (c).
Answer: (c) 2 and 3.
Why each option is right or wrong
- (a) Incorrect. Ferns and mushrooms both need some substrate (soil or organic matter).
- (b) Incorrect. Moss also survives on soilless surfaces (bare rock, walls, bark).
- (c) CORRECT. Lichens (fungus-alga symbiosis) and mosses (rhizoid-anchored) are both pioneer species that survive on rocks, walls, tree bark without soil.
- (d) Incorrect. Ferns and mushrooms need substrate; only lichens and mosses are truly soilless.
Key point
Pioneer species = lichens + mosses (grow on bare rock). Lichens = fungus + alga symbiosis, secrete acid to weather rock. Mosses = non-vascular, use rhizoids. Ferns and mushrooms need substrate/soil.
Remember
Lichens (2) and mosses (3) are pioneer species that can grow on bare surfaces without soil - rocks, walls, tree bark. Lichens are fungus-alga symbioses that secrete acid to weather rock. Ferns (1) and mushrooms (4) need substrate. Answer: 2 and 3.
Common mistakes
- Assuming all plants need soil. Mosses and lichens are pioneer species that colonise bare rock and initiate soil formation.
- Confusing lichens with fungi. Lichens are SYMBIOTIC organisms (fungus + alga), not pure fungi.
- Not knowing lichens are bio-indicators of air pollution - they die in high SO2 environments.
Exam tip
Ecological succession begins with lichens on bare rock. Lichens acid-etch rock, create thin soil, then mosses colonise, followed by grasses, shrubs, and finally trees (climax community). This is 'primary succession'. Rare in Indian syllabus but often tested.
Sources
- NCERT Class XI Biology - Chapter 22: Plant Growth and Development
- NCERT Class XII Biology - Chapter 14: Ecosystem