LSAT Explanation PT 26, S3, Q18: A stingray without parasites is healthier

LSAT Question Stem

Which one of the following, if true, most helps to reconcile the discrepancy indicated above? 

Logical Reasoning Question Type

This is a Paradox question. 

Correct Answer

The correct answer to this question is A. 

LSAT Question Complete Explanation

The passage presents a discrepancy: stingrays without parasites are healthier than those with parasites, but the lack of parasites in stingrays is an indicator that the ecosystem is under environmental stress (e.g., pollution). The question type is a Paradox question, which asks us to find an answer choice that helps reconcile this discrepancy.

Let's analyze each answer choice:

a) During part of their life cycles, the parasites of stingrays require as hosts shrimp or oysters, which are environmentally vulnerable organisms.

This answer choice helps reconcile the discrepancy by suggesting that the absence of parasites in stingrays could be due to the parasites' other necessary hosts, shrimp or oysters, being affected by environmental stress. If the shrimp and oysters are affected, the parasites cannot complete their life cycle, leading to a lack of parasites in stingrays. This would mean that the stingrays are healthier due to the absence of parasites, but the lack of parasites indicates a stressed ecosystem. This answer choice is the correct one.

b) A stingray is a free-ranging predator that feeds on smaller organisms but has few predators itself.

This answer choice does not address the discrepancy between the health of stingrays and the environmental stress indicated by the lack of parasites. It only provides information about the stingray's position in the food chain.

c) A parasite drains part of the vitality of its host by drawing nourishment from the host.

This answer choice explains why a stingray without parasites would be healthier, but it does not address the environmental stress indicated by the lack of parasites.

d) An ecosystem can be considered stressed if only a few species of very simple organisms can live there.

This answer choice provides a definition of a stressed ecosystem but does not explain how the lack of parasites in stingrays can indicate both the health of the stingrays and the stress in the ecosystem.

e) Since the life of parasites depends on that of their host, they need to live without killing their host or else to reproduce and infect other individuals before their own host dies.

This answer choice explains the relationship between parasites and their hosts but does not address the discrepancy between the health of stingrays and the environmental stress indicated by the lack of parasites.

In conclusion, answer choice A is the best option to help reconcile the discrepancy, as it provides a connection between the lack of parasites in stingrays and the environmental stress affecting other hosts in the ecosystem.