Which photoreceptors enable vision of high acuity and colour?

Question

BlackTom AI · Accepted Answer

Cones are responsible for high-acuity, colour vision.

1. Relevant knowledge points and concepts
- Two primary retinal photoreceptors: rods and cones.  
- Cones mediate photopic (daylight) vision, colour discrimination, and fine spatial resolution. There are three cone types (S, M, L) with different opsins tuned to short, medium, and long wavelengths.  
- Rods mediate scotopic (low-light) vision, are highly light-sensitive, contain rhodopsin, but do not support colour vision and have poorer spatial acuity.

2. Step‑by‑step reasoning
- Spatial acuity depends on receptor density and the degree of convergence onto bipolar and ganglion cells. In the fovea, cones are densely packed and often have near one-to‑one connections with bipolar and ganglion cells, producing small receptive fields and high spatial resolution.  
- Colour vision requires multiple photoreceptor types with different spectral sensitivities. The three cone opsins provide wavelength-dependent signals that the brain compares to perceive colour.  
- Rods, by contrast, are numerous outside the fovea and converge massively onto bipolar cells; this improves sensitivity but blurs spatial details and cannot provide spectral comparisons needed for colour.

3. (Calculations) No numerical calculation is required; the argument is anatomical and physiological.

4. Why the correct answer is correct
- Cones’ high density in the fovea, one‑to‑one wiring, and three distinct photopigments directly enable both high visual acuity and colour discrimination under well‑lit (photopic) conditions. These features are the mechanistic basis for the stated functions.

5. Why the other option is incorrect
- Rods are specialized for dim‑light sensitivity, not colour or fine detail. They lack multiple spectral opsins for colour discrimination and their high convergence reduces spatial resolution.

6. Conclusion
- Therefore the correct choice is b. Cones, which matches the provided answer.

Which photoreceptors enable vision of high acuity and colour?Single choice

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