Focus Exercise 7.25

[Stella Nguyen 1J]

Hi everyone!

I was very confused on how to approach this problem and come up with an explanation, so I was wondering if you guys could explain your thought process on how you guys understood this question?

2.25: Vision depends on the protein rhodopsin, which absorbs light in the retina of the eye in a reaction in which one form, metarhodopsin I, is converted to another, metarhodopsin II. The half-life of this reaction in cattle eyes is 600 μs at 37 °C but 1 s at 0 °C, whereas in frog eyes the same process has a half-life that differs by a factor of only 6 over the same temperature range. Suggest an explanation and speculate on the survival advantages that this difference provides the frog.

Thank you!

[Josh Chou 3K]

The first thing I got from the problem is that the half-life reaction in cattle eyes changes drastically between 0°C and 37°C (1s/600μs = 1.67 x 10³). The problem noted that the half-life reaction in the eyes of a frog only changes by a factor of 6 over the same temperature interval, which means that the frog's vision is much more constant and stable despite changes in temperature, and it gives the frog a survival advantage because it can see well in a wide range of temperatures. I just said in my answer that it had to do with frogs being amphibians and cattle being mammals, but the book says something about frogs being poikilotherms, which is a term I've never heard before