CAPF AC 2021 Q26: Science & Technology – Biology
Which one of the following pairs is not correctly matched?
- (a) Positively phototropic : Shoot
- (b) Positively geotropic : Root
- (c) Chemotropic : Pollen tube
- (d) Hydrotropic : Flower
Answer: (d) Hydrotropic : Flower
Explanation
Tropic movements in plants
How to think: a tropic movement is growth towards or away from a stimulus.
Match each plant part with the stimulus it grows towards.
Water is searched for by the root, not by the flower.
| Movement | Stimulus | Plant part that shows it |
|---|---|---|
| Phototropism (positive) | Light | Shoot |
| Geotropism (positive) | Gravity | Root |
| Chemotropism | Chemicals | Pollen tube growing towards the ovule |
| Hydrotropism | Water | Root |
So the wrong pair is: Hydrotropic : Flower.
Answer: (d) Hydrotropic : Flower.
Why each option is right or wrong
- (a) Incorrect. This pair is right: the shoot grows towards light.
- (b) Incorrect. This pair is right: the root grows downwards with gravity.
- (c) Incorrect. This pair is right: the pollen tube grows towards chemicals from the ovule.
- (d) CORRECT. This pair is wrong: roots, not flowers, grow towards water.
Key point
Shoot: positively phototropic, negatively geotropic. Root: positively geotropic and hydrotropic. Pollen tube: chemotropic.
Remember
Roots follow water and gravity; shoots follow light.
Common mistakes
- Missing the word not and marking a pair that is correctly matched.
- Mixing up hydrotropism (water) with phototropism (light).
- Forgetting that the pollen tube is the standard example of chemotropism.
Exam tip
Educated guess: a flower does not move in search of water. The part of a plant that looks for water is always the root.
Sources
- NCERT Class X Science — Control and Coordination (movement due to growth)
- NCERT Class XI Biology — Plant Growth and Development