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Structure of the Eye
Concepts tested here
- Rods and cones
All Questions
2008 AIPMT 1 question
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Which one of the following is the correct difference between Rod cells and Cone cells of our retina?
(Each option gives a feature, followed by its description for rod cells and then for cone cells.)The retina has two types of photoreceptor cells, rods and cones.
Rods are responsible for twilight (scotopic) vision, i.e. vision in poor light. They contain the purplish-red pigment rhodopsin (visual purple), a derivative of vitamin A.
Cones are responsible for daylight (photopic) vision and colour vision, and they give sharp, detailed vision in bright light. They contain the pigment iodopsin (photopsin). So the overall function is correctly stated.
Distribution is wrongly stated: cones are densely packed at the centre of the retina (fovea of the macula lutea), while rods are more numerous in the peripheral parts.
Visual acuity is wrongly stated: acuity (resolution) is high for cones and low for rods.
Visual pigments are interchanged in the last statement: rods contain rhodopsin and cones contain iodopsin.
So the correct difference is the one on overall function: rods for vision in poor light, cones for colour vision and detailed vision in bright light.