Re: Rats injected with morphine exhibit decreased activity of the immune

Understanding the passage

Rats injected with morphine exhibit decreased activity of the immune system, the bodily system that fights off infections.
When rats are injected with morphine, the activity of their immune system decreases.
The immune system is the bodily system that fights off infections.
Inference: Rats injected with morphine becomes more susceptible to infections.
These same rats exhibited heightened blood levels of corticosteroids, chemicals secreted by the adrenal glands
The rats which are injected with morphine also showed increased blood levels of corticosteroids.
Corticosteroid is a chemical secreted by the adrenal glands in a body.
Since corticostebroids can interfere with immune-system activity, scientists hypothesized that the way morphine reduces immune responses in rats is by stimulating the adrenal glands to secrete additional corticosteroids into the bloodstream.

Morphine stimulates the adrenal glands to secrete additional amounts of corticosteroids into the bloodstream of the rats.
Since corticosteroids can affect the immune system, scientists have come up with a hypothesis that morphine is responsible for the decreased activity of the immune system in rats.
Conclusion: Scientists hypothesized that morphine decreased the immune system activities by stimulating the adrenal glands to secrete additional amounts of corticosteroids into the bloodstream.

Pre-thinking

Falsification Scenario

In what scenario will morphine NOT decrease the immune system activities by stimulating the adrenal glands to secrete additional amounts of corticosteroids into the bloodstream?

Given that:
(i)Rats injected with morphine show decreased activity of the immune system.
(ii)Rats injected with morphine also show increased blood levels of corticosteroids.
(iii)Corticosteroids are chemicals secreted by the adrenal glands.
(iv)Corticosteroids affect the immune system.

Though Process

Since rats, which are injected with morphine, showed decreased activity of the immune system and also showed increased blood levels of corticosteroids. And since corticosteroids are chemicals secreted by the adrenal glands which affect the immune system, scientists hypothesized that these elevated levels of corticosteroids are a result of the injected morphine.

Falsification condition: What if morphine is directly affecting the immune system even before additional corticosteroids are secreted into the bloodstream?
In this case, corticosteroids are not responsible for affecting the immune system because of morphine, which directly impacts and decreases the activity of the immune system. This condition would break down the conclusion.

Assumption: The morphine is not affecting the immune system directly even before additional corticosteroids are secreted into the bloodstream.

Answer choice analysis

(A)Injecting morphine into rats that already have heightened blood levels of corticosteroids and then observing their new blood levels of corticosteroids INCORRECT
If rats already have heightened blood levels of corticosteroids, then observing their new blood levels of corticosteroids will not prove whether stimulation of the adrenal glands are responsible for the decrease in the immune system activities after morphine is injected.

(B) Testing the level of immune-system activity of rats, removing their adrenal glands, and then testing the rats' immune-system activity levels again INCORRECT
The scientists hypothesize that morphine decreases immune system activities. This experiment does not involve morphine; therefore, this experiment is irrelevant.


(C) Injecting rats with corticosteroids and then observing how many of the rats contracted infections INCORRECT
We already know that corticosteroids impact the immune system activities. The hypothesis is about how morphine impacts corticosteroid levels, which, in turn, impacts the immune system. This experiment does not involve morphine; therefore, it is irrelevant.


(D) Removing the adrenal glands of rats, injecting the rats with morphine, and then testing the level of the rats' immune-system responses CORRECT
Variance test
oYes The level of the rats' immune-system responses decreases after removing the adrenal glands and injecting them with morphine.
oSince removing the adrenal glands ensure that additional corticosteroids are not secreted into the bloodstream, it would be clear to us that morphine is directly responsible for the decrease in immune system activities. This result would weaken the hypothesis of scientists.
oNo - The level of the rats' immune-system responses did not decrease after removing the adrenal glands and injecting them with morphine.
oIn this case, the hypothesis that corticosteroids and the adrenal glands are responsible for the decrease in the immune system activities is strengthened.

(E) Injecting rats with a drug that stimulates immune-system activity and then observing the level of corticosteroids in their bloodstreams INCORRECT
This option proposes a reverse experiment that will not help us evaluate the hypothesis because this experiment will determine how the level of corticosteroids impacts the immune system activities and not how morphine impacts the adrenal glands, which in turn, impacts the immune system activities.

Cheers!