An in vitro experiment involves making observations of events in a
a. test tube
b. growth chamber
c. living organism
d. total vacuum

A; test tube

Explanation:

In-vitro is defined as a technique of performing a given procedure in a controlled environment outside of a living organism. It does not correspond to the circumstances you would usually see in a living organism (since it is most likely in a test tube). This means that an in-vitro experiment could not be applied in a growth chamber in which outside/environmental factors affect the whole organism. You can also eliminate C since in vitro is exclusively taken place outside of a living organism. For D, you most likely wouldn't be able to observe much in a total vacuum as organisms work under regular Earth atmospheric conditions and a total vacuum would not accommodate that as it has a lower pressure.

i believe it would be the lungs.