Question

airplanes have pressurized cabins for passenger safety while flying high in the atmosphere

Answer 1

It's because the air at commercialairplane altitudes (25000–40000′) is too thin for humans to breathe. Bycompressing the air in the cabin, the “cabin altitude” is more like 6000–8000′ which we can breathe without supplemental oxygen masks. At highaltitudes, the partial pressure of Oxygen reduces.