Self-study
Scientist: Some colonies of bacteria produce antibiotic molecules called phenazines, which they use to fend off other bacteria. ██ ███████████ ████ ██████████ ████ █████ ██ █████████ █████████ ████ ████ ████████ ████████ ██████ ██ █████████ █████████ ██ ███ ███████████ ███████████ ███ ███████
Stimulus Summary
A bacteria colony is a clump of bacteria. The bacteria on the outside edge are in direct contact with the surrounding environment, so they can pull nutrients from it directly. The bacteria buried in the interior can't, since they're walled in by their neighbors.
Some colonies produce phenazines, antibiotic molecules that they use to fend off rival bacteria. That's the established function. The scientist's hypothesis is that phenazines also have a second function: acting as molecular pipelines that deliver nutrients from the surrounding environment to the interior bacteria that can't reach the environment on their own.
Anticipation
This is a Strengthen question, so we want evidence that makes the pipeline hypothesis more plausible. The hypothesis is making a specific claim, that phenazines deliver nutrients to interior bacteria, so the most natural strengthener would point at that function directly. Maybe evidence that phenazines actually transport nutrients, or that interior bacteria in phenazine colonies are getting nutrients in a way they otherwise couldn't.
That's the obvious direction, but strengtheners can come from less obvious angles too. Stay open in the answers. The filter to apply firmly is on the existing function: anything that just confirms phenazines fend off rival bacteria isn't going to help, since we already know that. We're trying to support the new claim about nutrient delivery.
23.
Which one of the following, ██ █████ ████████ ███ ████ ███████ ███ ███ ███████████ ███████████
a
Bacteria colonies that ██ ███ ███████ ██████████ ████ ████████ █████████ ████ ██████████ ███ ██████ ██ ████████ ████ ███ ██ ██████ ███████ ████ ███ ███████████ ████████████
This supports the hypothesis by showing that colonies without phenazines use an alternative method to get nutrients to their bacteria. This makes the theory that phenazines give interior bacteria access to nutrients more plausible. When there's no pipeline, the colony grows in a wrinkled shape, which puts more bacteria on the edge in direct contact with the environment where the nutrients are.
The fact that non-phenazine colonies have this kind of workaround is evidence that phenazines fill that nutrient-access role. Both kinds of colony are solving the same problem (feeding interior bacteria); one is doing it through shape, the other (according to the hypothesis) through molecular pipelines.
Plausibility
Plausibility
Presenting evidence that corroborates (in Strengthen) or conflicts (in Weaken) with the author's hypothesized explanation or the predictions that follow from that explanation.
b
The rate at █████ █ ████████ ██████ ████████ ██████████ ██ ██████████ ██ ███ ██████ ██ ███████ ████████ ██ ███ ███████████ ███████████ ███████████ ███ ███████
This connects phenazines to the antibiotic function we already know about, not the new pipeline claim. The more rival bacteria in the environment, the more antibiotics the colony makes. This tells us nothing about whether phenazines also deliver nutrients to interior bacteria.
c
When bacteria colonies ████ ██ ███ ███████ ██████████ ███ ██████ ██ █████████████ █████ ████ ████ ██ ███████ ██ ████████ ████ ██ ███████ ███████████
If anything, this is in the direction of a weakener. If phenazines really were piping nutrients in, you'd expect phenazine colonies to grow faster than non-phenazine colonies, especially in nutrient-rich soil where the pipelines would have plenty to deliver. (C) tells us the two kinds of colony grow equally fast in those conditions, which suggests phenazines aren't providing any nutrient advantage at all.
d
Bacteria colonies that ███████ ██████████ ███ ██████ ████ ██ ████ ███ █████ ████████ ████ ███ ████████ ████████ ████ ██ ███ ███████ ███████████
This just confirms what the stimulus already told us. The first sentence establishes that phenazines are antibiotic molecules used to fend off other bacteria, so of course colonies that produce these antibiotics are better at fending off rivals. (D) restates the established function. The hypothesis we're trying to support is the new claim about nutrient pipelines, and (D) doesn't touch it.
e
Within bacteria colonies ████ ███████ ███████████ ████████ ████████ ███ ████ ██████ ██ ███ ████ ███ ████████ █████ ███ ██████
This is also in weakener territory. If phenazines were piping nutrients to interior bacteria, you'd expect those bacteria to be doing fine, or at least no worse than the edge bacteria with direct nutrient access. Learning that interior bacteria are more likely to die suggests that whatever phenazines are doing, they aren't keeping the interior bacteria well-fed. That cuts against the hypothesis.