Self-study
Microbiologist: Support Because heavy metals are normally concentrated in sewage sludge during the sewage treatment process, the bacteria that survive in the sludge have evolved the unusual ability to resist heavy-metal poisoning. ███ ████ ████████ ████ ████ █ ██████ ██████████ ██ ████████████ ████ ████████ ████ ███ ██████████ ████████ ██ ███ █████ ██████ ██ ███ ██████ ██████ ███ ███████ ████████ █████ ██████████ ██ ████████████
Summarize Argument: Phenomenon-Hypothesis
The microbiologist hypothesizes that the bacteria’s exposure to heavy metals in sewage sludge caused them to develop antibiotic resistance. He supports this by saying that since heavy metals are concentrated in the sludge, bacteria that survive there have evolved to resist heavy-metal poisoning, and these same bacteria are resistant to antibiotics.
Notable Assumptions
The microbiologist assumes that heavy metal exposure can promote antibiotic resistance in certain bacteria. He also assumes that there are no alternative hypotheses to explain the observed correlation— that is, he assumes that there is not a third factor that causes both antibiotic resistance and heavy-metal poisoning resistance. He also assumes that the causal relationship is not reversed— that is, that antibiotic resistance does not cause heavy-metal poisoning resistance.
22.
Which one of the following, ██ █████ ████ ███████████ ███ ████████████████ █████████
a
Most bacteria that ███ ███ █████████ ██ ███████████ ███ ███ █████████ ██ ███████████ █████████ ███████
The microbiologist is only addressing those bacteria that are resistant to both heavy-metal poisoning and antibiotics. Even if (A) is true, it wouldn’t impact his conclusion that heavy-metal exposure causes antibiotic resistance in certain bacteria.
b
Bacteria that live ██ ██████ ██████ ████ ██ ████ ██ █████ ███████ ███ ██ ██ █████ ████████ ███████ ██ ██████ ███████ ███ █████████ █████████ ██ ███████ ███████████ █████████ ███ ████████████
This strengthens the hypothesis by providing a control group. If bacteria in sludge without heavy metals aren’t resistant to heavy-metal poisoning or antibiotics, it’s more likely that the heavy-metal exposure did cause antibiotic resistance in the bacteria in the other sludge.
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.
c
Antibiotic resistance of ████████ ████ ███████ ██ ██████ ██████ ██ █████ █████ ██████ ███ ████████████ ███████████ ██ █████ ██████████ ██ ███████████ ██████████
This weakens the microbiologist’s hypothesis by suggesting that the causal relationship is reversed. That is, (C) suggests that antibiotic resistance causes heavy-metal poisoning resistance, rather than the other way around.
Directionally wrong
Directionally wrong
Answers that, if they have any effect, do the opposite of what we want (weaken when we're trying to strengthen, or strengthen when we're trying to weaken).
d
Sewage sludge that ████████ ████ ██████████████ ██ █████ ██████ ██████ ██████ ████████ ███████████ ██████████████ ██ ████████████
This weakens the hypothesis by providing a plausible alternative explanation. If sludge that contains heavy metals also contains significant amounts of antibiotics, it’s likely that the antibiotics cause antibiotic resistance in the bacteria, not the heavy-metal exposure.
Directionally wrong
Directionally wrong
Answers that, if they have any effect, do the opposite of what we want (weaken when we're trying to strengthen, or strengthen when we're trying to weaken).
e
Many kinds of ████████ ████ ██ ███ ████ ██ ██████ ██████ ███ █████████ ██ ████ ███████████ █████████ ███ ████████████
This doesn’t strengthen the hypothesis that heavy-metal exposure caused antibiotic resistance in the bacteria. We don’t know if the bacteria described in (E) were exposed to heavy metals or not.