UPSC Prelims 2010 Q65: Environment & Ecology – Ecosystems & Ecology Concepts
- (a) Their growth in shady and dark places does not allow them to undertake sufficient photosynthesis and thus they depend on insects for nutrition.
- (b) They are adapted to grow in nitrogen deficient soils and thus depend on insects for sufficient nitrogenous nutrition.
- (c) They cannot synthesize certain vitamins themselves and depend on the insects digested by them.
- (d) They have remained in that particular stage of evolution as living fossils, a link between autotrophs and heterotrophs.
Answer: (b) They are adapted to grow in nitrogen deficient soils and thus depend on insects for sufficient nitrogenous nutrition.
Explanation
Why some plants are insectivorous
Certain plants (like pitcher plants, Venus flytrap) have evolved a specialized nutritional strategy.
| Option | Verdict | Reason |
|---|---|---|
| (a) Grow in shady/dark places, insufficient photosynthesis | Incorrect | This is not the actual reason; insectivorous plants typically grow in sunlit but nutrient-poor environments |
| (b) Adapted to nitrogen-deficient soils, depend on insects for nitrogen | Correct | Insectivorous plants typically grow in nitrogen-poor soils (like bogs/marshes); trapping and digesting insects provides the nitrogen they can't get from the soil |
| (c) Cannot synthesize certain vitamins, depend on digested insects | Incorrect | This is not the real biological basis for insectivory in plants |
| (d) Living fossils, a link between autotrophs and heterotrophs | Incorrect | This is an inaccurate, overly dramatic mischaracterization of their evolutionary status |
Why plants evolve insectivory:
| Point | Detail |
|---|---|
| Habitat | Nitrogen-poor soils (bogs, marshes) |
| Solution | Trap and digest insects for nitrogen |
| Still photosynthetic | They remain autotrophic for carbon/energy; insects supplement nitrogen only |
Answer: (b) They are adapted to grow in nitrogen deficient soils and thus depend on insects for sufficient nitrogenous nutrition.
Why each option is right or wrong
- (a) Incorrect. Insectivorous plants are not primarily shade-dwellers lacking photosynthesis; their issue is soil nitrogen deficiency.
- (b) CORRECT. These plants grow in nitrogen-poor soils and supplement their nitrogen needs by digesting trapped insects.
- (c) Incorrect. Vitamin synthesis is not the real basis for plant insectivory.
- (d) Incorrect. This 'living fossil' framing misrepresents their actual evolutionary adaptation to poor soils.
Key point
Insectivorous plants are adapted to NITROGEN-DEFICIENT SOILS (like bogs) and digest trapped insects specifically to meet their nitrogen needs — they remain fully photosynthetic for carbon/energy.
Remember
Plants become insectivorous mainly because they grow in nitrogen-deficient soils and need insects as a nitrogen source.
Common mistakes
- Attributing plant insectivory to insufficient light/photosynthesis, rather than soil nitrogen deficiency.
- Confusing the nitrogen-supplementation role with an unrelated vitamin-deficiency explanation.
- Mischaracterizing these plants as evolutionary 'missing links' rather than nitrogen-adapted specialists.
Exam tip
Insectivorous plants = normal photosynthesizers adapted to nitrogen-poor soils; insects supply nitrogen, not carbon/energy.
Sources
- NCERT Class XI Biology — Mineral Nutrition (insectivorous plants)
- Peter H. Raven, Ray F. Evert and Susan E. Eichhorn — Biology of Plants (W. H. Freeman)