Buff, Are you saying that if a sudden depressurization occurs at 35,000ft, donning the oxygen masks in the cabin by passengers will have no effect since the body cannot absorb it?
That is two questions in one, so I will break it down with my answer:
First, for the cabin to go to 35,000 immediately, a catastrophic failure would have had to occur. An example on a small aircraft would be loss of a main door; on a large aircraft, a fuselage section (Aloha 737, or a bomb). Loss of a passenger window or even a door on a large aircraft would not result in an instantaneous cabin altitude of, in this example, 35,000.
Second, within seconds of the failure, the pilots will be starting an emergency descent to get the aircraft to 10,000 or a safe altitude, whichever is higher.
So the direct answer to your question is No I'm not saying that, because the passenger will not experience 35,000 cabin pressure. But given the worst case scenario of an explosive decompression (cabin altitude rising instantly to ambient altitude), the reason to get the masks on is you only have a few minutes of useful activity before you lose consciousness. Once the mask is on, during the descent your body will be able to respire the oxygen coming from the mask on your face. It will not "go without" for any length of time.
If the human being is exposed to 35,000 (or any altitude in excess of 30,000') for any length of time, no amount of oxygen supplied to a face mask will keep you alive for long, unless you're wearing a pressure suit (like a fighter pilot or an astronaut).
If yes, why can't the body absorb it? and what is the point of having drop down masks?
With regards the body's ability to absorb oxygen in a rarefied atmosphere, I can pass along my knowledge, but I would suggest you acquire a reliable text on aviation medicine with a good section on high altitude effects on the human body. In short, for oxygen to be absorbed into the cells of the body, the air pressure outside the cell has to be greater than the pressure inside the cell. If the pressure inside the cell is greater than outside, the cell will expel oxygen. Therefore with prolonged exposure to 35,000 foot pressuization, the more you breathe in from the oxygen mask, the faster you will be breathing out oxygen from within your body, including all the O2 from the mask. Reason being the oxygen entering your lungs from the mask is not absorbed, and is consequently expelled when you breathe out. Eventually, you will lose consciousness, and death will follow. Oxygen supplied to the pilots is under pressure and by a mask that seals itself around the mouth/nose. That oxygen is delivered to the lungs under positive pressure, so is more effective than the free flow oxygen provided by drop down passenger masks.
However, in the example of the drop down passenger masks of which you asked, the oxygen flow will be on your face providing pure oxygen, diluted by any air entering the mask from the cabin atmosphere, for you to breathe once the airplane gets down to the lower levels. And again, from above, the reason to get the masks on is you only have a few minutes of useful activity before you lose consciousness. Once the mask is on, during the descent your body will be able to respire the oxygen coming from the mask on your face. It will not "go without" for any length of time.
Another question would be:
-In the case of rapid/explosive depressurization, i've read that almost everyone will die because of the cold temperature sweeping through the cabin before passengers will have a chance to don oxygen masks. Is this true?
That is too hypothetical for me to answer. However, an answer may be forthcoming if the NTSB is able to determine what happened with last week's LearJet loss. I can speculate that if a cockpit window failed completely (another extremely to the extreme rarity, with their double pane construction), the resultant shock of 1) the window coming back in your face at 500 knots and 2) the inrushing of -55 to -65 degree celsius air at that same speed, then there's probably not much anyone this side of Heaven will be able to do to save the day. Best case scenario, a human being cannot survive -55 celsius temperatures for very long without protective clothing. However, from my reading of the press reports on that LearJet loss, all of the aircraft windows as observed by the F16's seemed to be intact. All speculation, I'm afraid.
Most people have never experienced -55 celsius (-67 fahrenheit). I have, but not in an airplane - I worked in the high Arctic for a couple of years in the early 80's. Anyone who has lived in northern Alberta or the NWT, or northern Ontario might also have experienced these temperatures.
I hope you're still reading, and I apologize for being lengthy, but I can't think of a short answer to a complex question like you've asked! As you can see, there are many variables involved.
Hope this is more clear then when you first asked your first question!!