TBR Gases Expiration

[LuminousTruth]

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What is observed during normal expiration?
I. Total lung volume is less than tital volume
II. Internal pressure exceeds external pressure.
III. Moles of O2 exceed moles of CO2.

A) I
B) II
C) I and II
D) II and III

The answer was " B ".

I can see why I is NOT true and II IS true. But I do not understand part III. TBR says "expiration occurs to displace CO2,so it must have a greater mole fraction of CO2 than O2."

What does the "it" refer to? Is part III referring to within the body or outside of the body? I thought since expiration was removing CO2 out of the body to the outside, that would mean there would be MORE O2 than CO2 present.

Also, on a similar topic:

Can someone explain to me HOW greater pressure means denser air? For example, air underwater is said to have a higher external pressure, which means the air is denser and more concentrated.

 

[cheesier]

Greater pressure means denser air because if you compress air, its volume decreases while its mass remains constant. Lower volume w/ constant mass --> Higher density, and lower volume correlates with higher pressure.

CO2 is what you're getting rid of during expiration, not O2, so when you expire, you're getting rid of it and it is (mainly) what is filling your lungs, so 3 is wrong. It is referring to your lungs (poorly written by TBR here). In other words, right before you breathe out your red blood cells have shuttled CO2 to your lungs to be expelled and have taken most of the O2 into your bloodstream. That leaves your lungs with a lot of CO2 and not much O2.

edited bcuz i misread the question

 

[adrakdavra]

the answer is B
Also The deeper you go the more pressure , If a fluid is at rest, then all points at the same depth must be at the same pressure (otherwise it would be moving!). However the pressure WILL vary with depth: it will have the weight of the fluid on top of it. mass= density x volume = density x (area x hight)
the pressure at a depth ‘h' will be the atmospheric pressure + (rgh)

 

[cheesier]

the answer is C
Also The deeper you go the more pressure , If a fluid is at rest, then all points at the same depth must be at the same pressure (otherwise it would be moving!). However the pressure WILL vary with depth: it will have the weight of the fluid on top of it. mass= density x volume = density x (area x hight)
the pressure at a depth ‘h’ will be the atmospheric pressure + (rgh)

It can't be C because 1 is wrong since tidal volume only represents a small fraction of your total lung capacity, and therefore total lung volume is more than tidal volume. Only 2 is right.

 

[adrakdavra]

yes B