For several decades now, amphibian species worldwide have been in decline. A significant proportion of the decline seems to be due to the spread of the chytrid fungus, Batrachochytrium dendrobatidis (Bd). Chytrid sporangia reside within the epidermal cells of infected animals, animals that consequently show areas of sloughed skin.
They can also be lethargic, which is expressed through failure to hide and failure to flee. The infection cycle typically takes 4 to 5 days, at the end of which zoospores are released from sporangia into the environment. In some amphibian species, mortality rates approach 100 percent; other species seem able to survive the infection.

The question is incomplete, here is the complete question:

For several decades now, amphibian species worldwide have been in decline. A significant proportion of the decline seems to be due to the spread of the chytrid fungus, Batrachochytrium dendrobatidis(Bd). Chytrid sporangia reside within the epidermal cells of infected animals, animals that consequently show areas of sloughed skin. They can also be lethargic, which is expressed through failure to hide and failure to flee. The infection cycle typically takes four to five days, at the end of which zoospores are released from sporangia into the environment. In some amphibian species, mortality rates approach 100%; other species seem able to survive the infection. However, when adult amphibian skin harbors populations of the bacterium Janthinobacterium lividum (Jl), chytrid infection seems to be inhibited.

A researcher took water in which a Jl population had been thriving, filtered the water to remove all bacterial cells, and then applied the water to the skins of adult amphibians to see if there would subsequently be a reduced infection rate by Bd when frog skins were inoculated with Bd. For which of the following hypotheses is the procedure described a potential test?

a. Jl outcompetes Bd when both are present together on a frog's skin.

b. Jl cells infect and kill Bd cells when both are present together on frog skin.

c. A toxin secreted by Jl cells kills Bd cells when both are present together on frog skin.

d. The presence of Jl on frog skin causes a skin reaction that prevents attachment by Bd cells.

A toxin secreted by JI cells kills Bd cells when both are present together on frog skin. (c)

Explanation:

The question is simply asking us to match the best hypothesis that the researcher had in mind before conducting the experiment.

The answer to this question is simply based on the action of the researcher during the experiment. The researcher took water in which a Jl population had been thriving, filtered the water to remove all bacterial cells, and then applied the water to the skins of adult amphibians to see if there would subsequently be a reduced infection rate by Bd when frog skins were inoculated with Bd. The filteration of the water was to remove all the JI bacterial cells. This action disproves the hypothesis a, b and d in the options given above because all three hypotheses require the JI cells to be present along with the Bd cells all on the skin if the frog during the experiment, but it was just the filtrate of the water that was used, so most accurately, it can be said that while the JI cells thrived in the water, they produced toxins which remained in the filtrate after the bacterial cells have been removed, and the researcher hopes to find out if these toxins produced by the JI species will be bactericidal to the Bd species after inoculation. This hypothesis is also scientifically correct because most bacterial cells with high pathogenicity produce toxins that remain in their environment even after the bacterial cell is dead. and example is the Clostridium botulinum bacteria that produces the Botulinum toxin also known as Botox.

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