True or False: PO2 increases while the percentage of oxygen decreases as altitude increases.

The statement that "PO2 increases while the percentage of oxygen decreases as altitude increases" is false. As altitude increases, the total atmospheric pressure decreases, which in turn reduces the partial pressure of oxygen (PO2). While the percentage of oxygen in the atmosphere remains constant around 21% regardless of altitude, the lower atmospheric pressure results in a lower PO2. Thus, while the relative amount of oxygen does not decrease, its effectiveness in providing adequate oxygen to the body diminishes due to the reduced PO2.

In summary, as altitude increases, PO2 decreases due to a decrease in the total atmospheric pressure, which means less oxygen is available to breathe effectively, leading to potential hypoxia in unacclimatized individuals.