Say whether each statement belongs to the rods, to the cones, or to both…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Say whether each statement belongs to the rods, to the cones, or to both.
- It works in daylight.
- It works in twilight.
- It is the only cell in the fovea.
- It holds a photopigment made of opsin and retinal.
- It gives colour vision.
Need a reminder? The key ideaShow
Cones work in daylight and give colour vision, and rods work in twilight. A photopigment is opsin plus retinal. Light separates them, the permeability of the membrane changes, and the signal passes to the bipolar cells, the ganglion cells and the optic nerve. In a simple model of the eye, in dioptres, with in metres.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) The cones. Daylight vision is photopic.
Step 2. (b) The rods. Twilight vision is scotopic.
Step 3. (c) The cones. Only cones are packed in the fovea.
Step 4. (d) Both. Each photopigment is made of opsin, a protein, and retinal, an aldehyde of vitamin A.
Step 5. (e) The cones. The three kinds of cone give colour vision.
Answer: (a) cones; (b) rods; (c) cones; (d) both; (e) cones.
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