CAPF AC 2021 Q23: Science & Technology – Biology
Which one of the following is not a function of chlorophyll?
- (a) Splitting of water
- (b) Absorption of photon
- (c) Oxidation of carbohydrate
- (d) Conversion of light energy into chemical energy
Answer: (c) Oxidation of carbohydrate
Explanation
What chlorophyll does
How to think: chlorophyll is the green pigment of photosynthesis.
Photosynthesis builds carbohydrate.
Breaking carbohydrate down (oxidation) is respiration, which happens in the mitochondria.
So that one is not the work of chlorophyll.
| Event in photosynthesis | Role of chlorophyll |
|---|---|
| Absorption of light (photons) | Yes |
| Conversion of light energy into chemical energy | Yes |
| Splitting of water into hydrogen and oxygen | Yes, uses the absorbed energy |
| Reduction of carbon dioxide to carbohydrate | Follows from the above |
| Oxidation of carbohydrate | No, this is respiration |
Answer: (c) Oxidation of carbohydrate.
Why each option is right or wrong
- (a) Incorrect. Splitting of water happens in photosynthesis using energy trapped by chlorophyll.
- (b) Incorrect. Chlorophyll absorbs photons; that is its first job.
- (c) CORRECT. Oxidation of carbohydrate is respiration, not a function of chlorophyll.
- (d) Incorrect. Chlorophyll converts light energy into chemical energy.
Key point
Three events of photosynthesis (NCERT): absorption of light by chlorophyll, conversion of light energy to chemical energy with splitting of water, and reduction of carbon dioxide to carbohydrate. Oxidation of carbohydrate is respiration.
Remember
Chlorophyll builds food; it does not burn it.
Common mistakes
- Confusing reduction of carbon dioxide (photosynthesis) with oxidation of carbohydrate (respiration).
- Thinking splitting of water has nothing to do with chlorophyll.
- Forgetting that respiration takes place in the mitochondria, not in chlorophyll.
Exam tip
Educated guess: photosynthesis makes food, so any option that breaks food down is the odd one. Oxidation of carbohydrate breaks food down.
Sources
- NCERT Class X Science — Life Processes (autotrophic nutrition)
- NCERT Class XI Biology — Photosynthesis in Higher Plants