Self-study
Researchers studying artificial sweeteners have long claimed that the perception of sweetness is determined by the activation of a single type of receptor on the tongue, called a sweetness receptor. ████ ████ ████ ███████ ████ ███ █████ ██████████ ████████ ██ █████████ ███ ████████ ██ ████ ███ █████████ ████████ ███ ████ ███ █████ █████████ ████ ███ ████████ ██ ████████ █ █████████ ███ ███████ ████ █████████ ████ ██ █████████ ██ ███ ████ ███ ███████████ █████ ██ ████ ██████████ █ █████████ ██ █████ ████ ███ ████████ ██ ██████ ██ ████████ ███ █████████ █████████
Stimulus Breakdown
We're looking for an answer that is strongly supported by the stimulus, and to do that we can assume that everything in the stimulus is true. So let's start by getting clear on the facts:
(1) we perceive sweetness when a sweetness receptor on our tongue is activated;
(2) a single molecule of a sweet substance can activate at most one sweetness receptor;
(3) the fewer molecules it takes to activate a sweetness receptor, the sweeter a substance is;
(4) a newly-discovered substance needs only one molecule to activate one sweetness receptor.
Objective: Find a Strongly Supported Conclusion
To find the correct answer, we're looking for an answer choice which is strongly supported by one or more claims in the stimulus. We may need to combine claims to make an inference, but we won't need any assumptions or outside information.
The stimulus also allows us to make up-front predictions about what the right answer might be. Here, we can infer that the newly-discovered substance is as sweet as it's possible to get, by combining claims (2), (3), and (4). The new substance uses one molecule to activate one sweetness receptor. That means it's sweeter than substances which use several molecules per receptor. And it's not possible to use less than one molecule per receptor: any given molecule can only activate one receptor, so you can't split them across multiple receptors.
We can start by looking for our predicted answer, but it's always possible there might be another strongly supported claim. If we don't find the answer we're looking for, we should go back to process of elimination to find the correct answer. Anything that goes beyond the scope of the stimulus can be eliminated right away. Another useful test is to identify the specific claims in the stimulus that support an answer choice.
16.
Which one of the following ███████████ ██ ████ ████████ █████████ ██ ███ ██████████████ ███████ ██ ███ ██ █████ ██████ ███ █████
a
The more sweetness █████████ █ ██████ ███ ██ ███ ██ ███ ███████ ███ ████ ██████ ██ ██ ████ ████ ██████ ████ ████ █████ ██████████ ████████████
The stimulus doesn't mention pleasure at all, which means (A) goes beyond the stimulus' scope. A claim about pleasure can't be strongly supported by a stimulus that doesn't discuss pleasure.
b
In sufficient quantity, ███ █████████ ██ ███ █████████ ███ ████████ █ █████████ █████████
We have a lower limit for molecules activating sweetness receptors: we need
c
No substance will ██ █████ ████ ██ █████████ ██ ██ ███████ ████ ███ █████████ ███ ███████████ ████ ███████████
(C) combines several claims in the stimulus to draw a strongly supported conclusion. We know that
In other words, the stimulus defines a theoretical limit for how sweet a substance can be: one molecule per sweetness receptor. The new substance hits that limit, so it's impossible for any other substance to be sweeter. Equally sweet is the most that's possible.
d
A substance that ████ ███ ████████ █ █████████ ████████ ████ ████████ █ █████ ████████ ██ ███████ █████
The stimulus doesn't discuss other taste receptors; (D) goes beyond the scope of the stimulus. There's nothing to tell us that every substance has to activate taste receptors. It's entirely possible some substances are perfectly tasteless.
e
The more molecules ██ █ █████████ ████ ███ ████████ ██ ████████ █ ██████ █████████ █████████ ███ ████ ██████ ████ █████████ ████ ██ █████████ ██ ███
The problem with (E) is the word "bitter"—bitterness is not mentioned in the stimulus. And it's baseless to assume that bitterness is the opposite of sweetness for this purpose. As far as we know, it's entirely possible for a substance to be neither sweet nor bitter.
If (E) said "less sweet" instead of "bitter", it would be strongly supported by the claim that substances are sweeter when they need fewer molecules to activate a sweetness receptor. But because it relies on a new idea of bitterness, it's not supported.