"Surprising" Phenomenon
Rather than growing as expected once viruses were removed from the environment, the plankton population shrank.
Objective
The correct answer will be a hypothesis that explains why the plankton population shrank. The explanation must explain why plankton do better in an environment with viruses rather than one without viruses, likely through some beneficial feature of viruses.
A
Viruses in seawater help to keep the plankton population below the maximum level that the resources in the water will support.
Without viruses, plankton still would’t be able to expand beyond the maximum level water resources support. We need to know why the plankton population actually shrank.
B
Plankton and viruses in seawater compete for some of the same nutrients.
If plankton and viruses are competitors, then the plankton population should’ve grown without the viruses. Instead, it shrank.
C
Plankton utilize the nutrients released by the death of organisms killed by viruses.
Viruses kill organisms which in turn feed plankton. Without viruses, the plankton population starved. This explains why the plankton population shrank.
D
The absence of viruses can facilitate the flourishing of bacteria that sometimes damage other organisms.
The language here is very weak. We don’t know if bacteria flourished without the viruses, or if plankton are one of the organisms those bacteria can damage.
E
At any given time, a considerable portion of the plankton in seawater are already infected by viruses.
This doesn’t explain why the plankton population shrank without the viruses. If many members were already infected, we need some other reason why the plankton population shrank further once the viruses were gone.
Summarize Argument
The council member concludes that to prevent anarchy, the council must deny the Senior Guild’s request for an exception. As support, he says that granting this exception would lead to other, undeserved exceptions and eventually to exceptions to all kinds of city ordinances.
Identify and Describe Flaw
The council member’s argument is vulnerable to criticism because he never provides evidence to support the key assumption that granting the Senior Guild’s exception would inevitably cause the council to grant undeserved exceptions to all kinds of city ordinances. Similarly, he never gives reason to believe that granting the request would cause anarchy.
A
distorts an argument and then attacks this distorted argument
The council member never attacks, distorts, or even presents any argument made by the Senior Guild. Instead, he presents his own argument for why the Guild’s exception should be denied.
B
dismisses a claim because of its source rather than because of its content
This is the cookie-cutter “ad hominem” flaw. The council member doesn’t make this mistake. He argues that the Guild’s request should be denied, but he doesn’t do so by attacking the Guild itself. In fact, he concedes that the Guild deserves this exception.
C
presumes, without sufficient warrant, that one event will lead to a particular causal sequence of events
The council member assumes that granting the Senior Guild’s exception will lead to a particular causal sequence of events— all manner of other exceptions and anarchy. But he doesn't offer any reason to think that one will actually cause the other.
D
contains premises that contradict one another
The council member’s premises may not support his conclusion well, but they never contradict one another.
E
fails to make a needed distinction between deserved exceptions and undeserved ones
The council member actually does distinguish between undeserved and deserved exceptions by pointing out that the Senior Guild’s exception is deserved, while some others are not. He just fails to take that distinction into consideration in his argument.