* Oxygen is essential for respiration: Mice, like all mammals, need oxygen to breathe and survive. They take oxygen into their lungs where it's absorbed into the bloodstream.
* Direct uptake: When the mice breathe in the radioactive oxygen (O2), the radioactive atoms will directly enter their lungs.
It's important to note that the radioactive oxygen would likely also be found in other parts of the mice's bodies over time as it circulates in their bloodstream and is used in various metabolic processes. However, the lungs would be the first and most concentrated location for the radioactive oxygen to appear.
