Arrange the steps of vision in order. The photopigment separates into opsin and retinal…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Arrange the steps of vision in order.
(1) The photopigment separates into opsin and retinal. (2) The optic nerve carries impulses to the visual cortex. (3) The cornea and the lens focus light on the retina. (4) A potential difference is generated in the photoreceptor cell. (5) Action potentials arise in the ganglion cells. (6) The structure of opsin changes and the membrane permeability changes.
- Write the order of the numbers.
- Where does the brain recognise the image, and on what does it rely?
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 order is 3, 1, 6, 4, 5, 2. First the light is focused (3). Then the pigment separates (1), and the opsin and the membrane change (6). A potential difference arises (4), the ganglion cells make action potentials (5), and the optic nerve carries them (2).
Step 2. (b) The brain recognises the image in the visual cortex. It relies on earlier memory and experience.
Answer: (a) 3, 1, 6, 4, 5, 2; (b) the visual cortex, with earlier memory and experience.
Watch out. The action potentials start in the ganglion cells, and not in the rods and cones.
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