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Which of the following descriptions of photoreceptors in the eye is NOT correct?  

Select one:
a. Rods are concentrated in the fovea of the retina and function well in dim light.
b. Rods are concentrated at the periphery and function well in dim light.
c. Cones are concentrated in the fovea of the retina and function to detect colours.
d. Rods are sensitive to light and register black and white. Cones detect colours.

5 years ago

Answered By Kevin G

Biology is a subject with a large emphasis on memorization so much of the time, either you kow the information or you don't. However, there are ways around this when it comes to questions like these.

Whenever you approach the type of question where most information is correct and you don't know the answer, it's often a good idea to approach it from a logical perspective. 

Notice that answers (a) and (b) seem to be mutually exclusive (can't both be true) since the term 'concentrated' that they use is relitive to the rod/cone ratio of the rest of the eye.

In other words, if there were a lot of rods in both the fovea and the periphery, then the word concentrated wouldn't be appropriate since the term relies on a place where rods are not concentrated to have any meaning. 

You can therefore narrow it down to one of (a) and (b) and we can now see that they are testing if you know where rods are concentrated in the eye. 

Notice now that we can take all of (d) and (c) and the common parts of (a) and (b) to be true.

Given that (d) states that "rods are sensitive to light" and (a) and (b) both state that they "function well in dim light," it is unlikely that rods would be concentrated in the focal point of the eye where the light is the most intense. Our answer then is most likely (a)

So even if you don't actually know where the rods and cones are concentrated before hand, we can reason our way to the answer using the given information.

Hope this helps :) 

4 years ago

Answered By Aiea M

The cones are concentrated in the fovea and function best in bright light to detect colour. The correct answer is C.