Q.48 Match the following photoreceptors with their prosthetic
groups and spectral specificity.
| Photoreceptor | Moiety that absorbs light | Absorption (nm) |
|---|---|---|
| P. Phototropin | 1. Chromobilin | a. 400–500 |
| Q. Cryptochrome | 2. FAD | b. 600–800 |
| R. Phytochrome | 3. FMN | c. 500–600 |
- P-3-a, Q-2-a, R-1-b
- P-1-b, Q-1-a, R-3-b
- P-3-a, Q-1-a, R-1-c
- P-2-c, Q-1-c, R-1-a
Introduction
Photoreceptors are light-sensitive proteins that play a vital role in plant development and biological rhythms. Each photoreceptor contains a specific prosthetic group (chromophore) that absorbs light at a characteristic wavelength range. Questions based on matching photoreceptors with their chromophores and absorption spectra are common in competitive exams.
This article explains the correct matching and provides a clear explanation of all options, helping you understand the underlying biology rather than just memorizing facts.
Correct Answer
✔ Option (B): P-1-b, Q-1-a, R-3-b
Conceptual Explanation
P. Phototropin
-
Prosthetic Group: Chromobilin
-
Absorption Range: 600–800 nm
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Function: Controls phototropism, chloroplast movement, and stomatal opening.
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Explanation: Phototropins respond mainly to blue to far-red regions due to their chromophore properties.
Q. Cryptochrome
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Prosthetic Group: Chromobilin
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Absorption Range: 400–500 nm
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Function: Regulates circadian rhythms and flowering time.
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Explanation: Cryptochromes are blue-light receptors, hence absorb in the 400–500 nm range.
R. Phytochrome
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Prosthetic Group: FMN
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Absorption Range: 600–800 nm
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Function: Controls seed germination, shade avoidance, and flowering.
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Explanation: Phytochromes absorb red and far-red light, which lies in the 600–800 nm region.
Why the Other Options Are Incorrect
🔸 Option (A): P-3-a, Q-2-a, R-1-b
-
Incorrect prosthetic group assignments for phototropin and phytochrome.
🔸 Option (C): P-3-a, Q-1-a, R-1-c
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Phytochrome does not absorb in the 500–600 nm range.
🔸 Option (D): P-2-c, Q-1-c, R-1-a
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FAD is incorrectly assigned to phototropin; absorption ranges are mismatched.
Quick Memory Tip
| Photoreceptor | Light Type | Chromophore |
|---|---|---|
| Phototropin | Blue/Far-red | Chromobilin |
| Cryptochrome | Blue | Chromobilin |
| Phytochrome | Red/Far-red | FMN |
Final Takeaway
Understanding which chromophore absorbs which wavelength is the key to solving photoreceptor matching questions. The correct combination here is Option (B) because it accurately aligns photoreceptors with their prosthetic groups and spectral specificity.
