PT120.S2.P4.Q19

PrepTest 120 - Section 2 - Passage 4 - Question 19

Hide analysis
P1

Until recently, biologists were unable to explain the fact that pathogens—disease-causing parasites—have evolved to incapacitate, and often overwhelm, their hosts. ████ ████████ ██ ██ ████ ████ ███ ██████████ ████ ██ █████████████ █████████████████ ██ ████████ ████ ███ ████████ ██████████ ███████ █ ██████ ████████████ ████ ████ ██ █████ ██ ███ ████ ████ █████████ ████ ██ ███ ████ █████ █████ ████ ███ ████ ██████ ███ █████████ █████████ ████ ██████ ███████ █████ █████ ███████ ███

Puzzling Phenomenon · Pathogens incapacitate and kill hosts
This is puzzling because the prevailing view is that parasites need their hosts for long-term survival.
████ ███████████ ████████ ████████ ████ █████████ ████ ██ █ ████████ ██████████ ██ ███████████ ██ ██ █████ ███ ████ ██ ██████ ███████ █████ ██ █████ █████ ███████ ████████████ ███████ ██ ███ ███████████ ███ ██ █ █████ ██ ████████████ ████ ███ █████ ████ ████████ ███ ████ ██ █████████ █████████ ████ ███ ██████ ███████████████ ████ ████████ ████████ ████ ████ █████████████ █████████ ███ ███████ ████████████ ████████

Hypothesis · Trade-off
Pathogen can cause hosts to be very sick or even die if it can spread to a new host. So it's trading away staying in the current host for jumping to a new host.
P2

███ ███████████ ██ ████ ███████████ ██ ████ █ ██████████ ███████████████ ████████ ██ ████████ █ ██████ ████████ ███ ████████████ ███████ █ ████████ ██ ███ ████ ██ █████████████ ███

Implication · Virulence is function of mode transmission
Virulence means the ability to defeat the host's defenses and incapacitate the host.
███ ████████ █████████████ █████ █████ ███ ██████ █████ ███████ ████████ █████████ ███ ████████████ ██ ██████ ██ █ ██████████ ██████████ ██ ███████████ ██ █ ████████ ████ ████ ███ ████ ██ ███ ██████ ██ █████ ████ ███ █ ████ ███ █████████ ██ ███ ████████████ ████████ ████ ███ ████ ███ ██████ ████ ███ ██ ████████████ ███ ███████ ██ ██ ███████████ █████████ ███ ██████ ████ ██ ████████ ██ ███████ ███ ████████

Example · Close contact transmission requires low virulence
Rhinoviruses (common cold) requires physical contact for transmission. Hence, it cannot be too virulent. If it were, then the host would be confined in solitude (or die) and the virus would not be able to jump to a new host. It needs to be only mildly virulent so that the host can help it jump to new hosts.
P3

███ ████████ ███ █████ ████ █████████ ███ ███████████ ██ █ ███████████ ████████ ████ ███ █████ ███ ████████ ██ ██████████ ██████ ███ ███ ████████ █ ████████ ███████ ██ █████ ███████████ ██ █ ████████ ██████████ ██ ███████████ ████ ███ █████ ████ ██ ████████████ ██ ███ █████ ████ █████ ███ █████ ██ █ ████████ █████ ███ ████ ███ █████████ ████ ████ ██ ███ ████ █████ ██ ██████ ██ ████ █████████████ ███ █████████ ██ ██████ ██ ██ ████ ███████ ███████ ███ ████████ ███ ██████████ ██ ████ █████████████ ██ ███ ████ ████ ███ ████████ ███████ █ ████ ████ ██ ███ █████████ ██████████ ███ █████ ██ ████████████ ██ ███ ██████

Example · Vector transmission requires high virulence
If a pathogen can be transmitted via a vector (e.g., mosquito), then virulence can and perhaps must be high. It needs to reproduce so extensively (and hence severely harm the host) such that the vector (e.g., mosquito) can acquire enough of the pathogen to transmit it to a new host.
P4

█████ ███████ ██████████ █████████ ████████ ███ ██████████ ████ ████████████ █████████ ████ ██ ██ ████ ████████ ████ ████████ ███████████ ███████████████████ ███ ██████ ██████ ██ ████████ ██████ ██████ ███████ ███ ████████ █████████ ███ ███████ ██ ██████ ███████████ ███ ████████ ███████████ █████████ ████ ██ ██████████ ███ ████████████ ████████ ███ ██ ████ ██ ███████ ██████████ ████ █████ ████ ███ █████ ██████████ ███████ ████ ███ ████ ██ ██████ █████ ███████ █████ █████ █████ █ ███ ████ █████ ██████ ███████ ███████ ██ █ ███████ ███████ ███ █████████ ██ █████ ██████████ ████ ██ █████ ███ ███████ ██████████ ███ █████ ██ ██████ ██████ ████████████ ████ █ ███ ████████████████ ███ █████████ ██ ██ ███████ ██████████ ████ ████ ██ █████████████ ████ █████ ███ ████ █████████ ██ ███ ██████████

Anomalies · "Sit and wait" pathogens
In general, the literature supports the hypothesis. But "sit and wait" pathogens like diphtheria and tuberculosis are directly transmitted yet lethal. They can do this because they can survive outside their hosts for up to months. This makes them the most dangerous kind of pathogen.
Passage Style
Phenomenon-hypothesis (RC)
Single position
Show answer
19.

Which one of the following ████ ██████████ ██████████ ███ ████ ████ ██ ███ ████████

a

A new hypothesis █████ ███ ███████████████████ ████████ ██ ████ █████████ ████████ ████ ████████ ███████████ █████████ ███ ████ ██ ████████ ██ ████████████ ██████████ ███ ██ ███ ████████ ███████ ██ ███████ ███████ █ ████ ███ ████ ███████ ██ █████

Anti-supported. Although there are some directly transmitted pathogens that can be just as lethal as vector-borne pathogens, this is typically not the case. Because (A) isn’t supported, it can’t be the main point.

7%
b

A new hypothesis █████ ███ ███████████████████ ████████ ██ ████ █████████ ████████ █████ █████ ████ █████████ █████████ ██ ███████████ ██ ██ █████ █████ █████ ██ ██████ ███████ ████ ██ ████ ██ ████ ████ ██████████ ███████ █ ██████ ███████████ ████ █████ ██████

Not supported. The new hypothesis doesn’t suggest that “most” pathogens incapacitate their hosts. Rather, it tries to explain how the pathogens that are known to incapacitate their hosts can still survive.

2%
c

A new hypothesis █████ ███ ███████████████████ ████████ ██ ████ █████████ ████████ ████ ████ ███ ████ ██ ███████ ████████████ ███████ ███████ ████ █████████ ██ █ ████ █████ ██ █████████████ ██ █████ █████████████ ██████

This is close, but incomplete. The hypothesis is that pathogens that incapacitate their hosts can have reproductive success because they are able to reproduce to a sufficient level to have transmission to new hosts exceed the loss of pathogens from the host’s incapacitation. (C) is missing the transmission aspect of the hypothesis. It also fails to cover the implication of the hypothesis, which is discussed P2, P3, and P4.

8%
d

A new hypothesis █████ ███ ███████████████████ ████████ ██ ████ █████████ ████████ ████ ████ ███ █████████ ████ ██ ███████ ████████████ ███████ ██████ █████ ████████████ ██████ ███ █████ ██ ███ █████

Not supported. The new hypothesis suggests that pathogens that incapacitate their hosts can achieve reproductive success regardless of the death of their hosts — if they can reproduce at a high enough level to cause transmission to new hosts to exceed the loss of pathogens from the host’s death, they can succeed.

2%
e

A new hypothesis █████ ███ ███████████████████ ████████ ██ ████ █████████ ████████ ████ ████████ █████████ ██ █████████ █ ████████ ██ █████ ████ ██ █████████████ ████ ████████████ █████████ ███████ ████ ████████ ████ ████████ ███████████ ██████████ ██████ ███ █████ ████████ ███████████ █████████ ████ ██ ██████ ███████ █████ ██████

This is the only answer that is both supported and broad enough to capture the main point. The new hypothesis about host-incapacitating behavior does suggest that virulence depends on transmission, with vector-born pathogens usually more virulent than directly transmitted pathogens, with some exceptions.

82%

Confirm action

Are you sure?