Question

A stingray without parasites is healthier than it would be if it had parasites. Nevertheless, the lack of parasites in stingrays is an indicator that the ecosystem in which the stingrays live is under environmental stress such as pollution.

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


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

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

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

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

(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.

Answer 1

The absence of parasites in stingrays, while initially suggesting good health, may indicate broader environmental stress because the parasites have complex life cycles involving environmentally vulnerable organisms like shrimp or oysters. When these organisms are decimated by pollution, the parasites can't complete their life cycles, leading to their absence in stingrays.

Step-by-step explanation:

The discrepancy between a stingray appearing healthier without parasites, yet the absence of parasites indicating environmental stress in the stingray's ecosystem, can be reconciled. It's important to look at the relationship between the health of individual organisms, the role of parasites, and the broader ecosystem.

Answer (A), stating that during part of their life cycles, the parasites of stingrays require as hosts shrimp or oysters, which are environmentally vulnerable organisms, helps to reconcile the apparent discrepancy. If shrimp and oysters are affected by pollution or other forms of environmental stress, they may not survive to serve as intermediate hosts for the parasites, which in turn could explain the absence of parasites in stingrays. This situation might lead to stingrays appearing healthier due to a lack of parasitic infections, but this absence would indeed be an indicator of broader environmental problems.