IGCSE BIOLOGY DOUBTS HERE !!!!

[astarmathsandphysics]

Hi
I came across a question in a past biology theory paper today;

'State how many times a red blood cell must pass through the heart when it travels from the lungs and returns to the lungs'

and also:

'At high altitudes there is less oxygen in the air than at sea level.
Suggest how this might affect the uptake of oxygen in the alveoli'

Thanks :DDD

Ist. Twice - on the way there and on the way to the body.
2nd. Think it would be reduced. I saw a program yesterday. If oxygen level falls below 80% saturation, you are in danger of not being able to think straight.

[MalloryKnox]

Okay, thanks. xD
quickly... - why would the oxygen be different at sea level, than at ground level?