If a person were skiing high up in the mountains, she might feel that she is having trouble breathing (getting enough oxygen in her blood). This is because the:

Question

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At high altitude, there is a lower atmospheric pressure which results in a decrease in available oxygen molecules in the air. This lowers the partial pressure of oxygen (PO₂) and reduces the diffusion gradient between the blood and the atmosphere. This makes it harder for oxygen to diffuse across the lung membrane and into the bloodstream, leading to the feeling of difficulty breathing.

If a Person Were Skiing High Up in the Mountains