PrepTest 110, Section 3, Question 19
Light is registered in the retina when photons(54 more words not shown)
Which one of the following(9 more words not shown)
- AThe temperature of(13 more words not shown)
- BThe visual systems(20 more words not shown)
- CAs the temperature(14 more words not shown)
- DRhodopsin molecules are(21 more words not shown)
- EMolecules of rhodopsin(11 more words not shown)
Reading the argument
The eye can register a signal even when no light has arrived. That's the problem to track here.
First, photons hit rhodopsin and change the molecules' shape. That is how light is registered. But ordinary molecular motion can also change the shape without a photon hitting the molecule. The system can therefore get an error from a change that wasn't caused by light.
Now add the temperature fact. Higher retinal temperature means more molecular motion. More of the motion that can produce these false signals gives me a reason to expect more errors. So my prediction is that a warmer retina will be more error-prone.
What we’re looking for
We're asked what is most strongly supported. The answer might connect those facts, as my prediction does, or it might stay closer to one individual fact. Either is possible. What matters is that we don't add an unsupported claim about some other aspect of how the eye works.
Working the answers
- A
The passage connects retinal temperature with molecular motion, not the amount of light absorbed with retinal temperature. Light can trigger the shape change, but so can motion without light. We cannot use the information about temperature and motion to conclude that absorbed light determines the temperature.
- BCorrect
These animals' body temperatures match their surroundings. In hot surroundings, their retinas will therefore be warmer than in cold surroundings. The warmer retinas have more molecular motion, which can change rhodopsin's shape even without light striking it. That creates more opportunity for the errors the passage describes.
The temperature-matching qualification matters. Hot air alone wouldn't give us the same reason to expect a hotter retina in an animal that maintained a stable body temperature. B supplies the connection from the surroundings to the retinal temperature, then the passage supplies the connection to errors.
- C
More errors doesn't mean a slower response to light. The error described is a molecule changing shape without being struck by a photon. We aren't told that rising temperature slows the response when a photon does hit the molecule. C changes which feature of the process we are measuring.
- D
Nothing connects retinal surface area to rhodopsin's sensitivity to light. A larger surface and more sensitive molecules are different features. We have information about temperature and molecular motion, not evidence that the size of the retina changes the sensitivity of each molecule.
- E
Describing one pigment doesn't establish that it is the only pigment present. There could be other naturally occurring pigments in the retina without contradicting anything here. We would need additional information to make E's exclusive claim.
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