CAPF AC 2021 Q84: Geography – Biogeography & Natural Vegetation
- (a) 2 and 4 only
- (b) 1, 3 and 4 only
- (c) 1, 2 and 3 only
- (d) 1, 2, 3 and 4
Answer: (d) 1, 2, 3 and 4
Explanation
Tropical rain forests
How to think: the surprising fact is that these rich forests stand on poor soil.
Heavy rain leaches the nutrients out of the soil.
Almost all the nutrients are locked in the living plants, not in the ground.
Once you accept that, all four statements fit together.
| Statement | Verdict | Reason |
|---|---|---|
| 1. Soils are quite infertile | Correct | Heavy leaching; nutrients are recycled quickly from leaf litter |
| 2. Evergreen vegetation, photosynthesis all year | Correct | No dry or cold season |
| 3. Described as deserts covered by trees | Correct | A phrase used because of the poor soil below the canopy |
| 4. Most productive land-based ecosystem | Correct | Highest net primary productivity on land |
Proof of the poor soil: when the forest is cleared for farming, crops fail after a few years.
That is why shifting cultivation is practised there.
Note: the bank earlier carried key (a); statement 1 is true, so the key is corrected to (d).
Answer: (d) 1, 2, 3 and 4.
Why each option is right or wrong
- (a) Incorrect. Statements 1 and 3 are also true; rain forest soils are poor.
- (b) Incorrect. It leaves out 2; the vegetation is clearly evergreen.
- (c) Incorrect. It leaves out 4; rain forests are the most productive land ecosystem.
- (d) CORRECT. All four statements about tropical rain forests are true.
Key point
Tropical rain forests: hot and wet all year, evergreen, layered canopy, greatest biodiversity and highest productivity on land, but leached infertile soils (oxisols or laterites). Nutrients sit in the biomass.
Remember
Rich forest, poor soil: nutrients are in the trees.
Common mistakes
- Assuming a dense forest must grow on fertile soil.
- Rejecting the phrase deserts covered by trees because rain forests are so wet.
- Mixing up high productivity of the forest with fertility of the soil.
Exam tip
Educated guess: statements 2 and 4 are certainly true, and only (a) and (d) contain both. Statement 1 is a standard textbook fact, which pushes the answer to (d).
Sources
- NCERT Class XI Geography — Fundamentals of Physical Geography, Chapter 15: Life on the Earth (biomes)
- NCERT Class XII Biology — Ecosystem (productivity and nutrient cycling)