Self-study
A stingray without parasites is healthier than it would be if it had parasites. █████████████ ███ ████ ██ █████████ ██ █████████ ██ ██ █████████ ████ ███ █████████ ██ █████ ███ █████████ ████ ██ █████ █████████████ ██████ ████ ██ ██████████
"Surprising" Phenomenon
Parasites in a stingray are not good for the stingray’s health, but the absence of parasites in a stingray is an indicator that the ecosystem the stingray lives in is under environmental stress.
Objective
The right answer will be a hypothesis that reconciles the seemingly contradictory ideas in the stimulus. It will explain how the presence of parasites in a stingray can be an indication of the stingray’s sub-optimal health while the absence of parasites in a stingray can indicate an ecosystem is of sub-optimal health.
18.
Which one of the following, ██ █████ ████ █████ ██ █████████ ███ ███████████ █████████ ██████
a
During part of █████ ████ ███████ ███ █████████ ██ █████████ ███████ ██ █████ ██████ ██ ████████ █████ ███ ███████████████ ██████████ ██████████
This helps reconcile the discrepancy. The absence of parasites in a stingray may indicate that, at the necessary point in their life cycles, the parasites could not find a shrimp or oyster to host them, as these potential hosts were adversely affected by environmental stress.
b
A stingray is █ ████████████ ████████ ████ █████ ██ ███████ █████████ ███ ███ ███ █████████ ███████
This does not offer information about parasites, which are a key feature of the discrepancy.
c
A parasite drains ████ ██ ███ ████████ ██ ███ ████ ██ ███████ ███████████ ████ ███ █████
The stimulus already says that stingrays with parasites are less healthy than they would be without parasites. The discrepancy involves the absence of parasites in stingrays indicating an environmentally stressed ecosystem, which (C) does not discuss.
d
An ecosystem can ██ ██████████ ████████ ██ ████ █ ███ ███████ ██ ████ ██████ █████████ ███ ████ ██████
(D) discusses what could cause an ecosystem to be considered stressed. However, it does not provide new information that reconciles the discrepancy. The stimulus also specifically addresses ecosystems under environmental stress, rather than simply being considered stressed.
e
Since the life ██ █████████ ███████ ██ ████ ██ █████ █████ ████ ████ ██ ████ ███████ ███████ █████ ████ ██ ████ ██ █████████ ███ ██████ █████ ███████████ ██████ █████ ███ ████ █████
This provides insight into the life of parasites, but not into the discrepancy discussed in the stimulus. (E) does not offer information that explains how parasites can be unhealthy for jellyfish but, when absent in jellyfish, indicate an environmentally stressed ecosystem.