One difference between the air in a pulminary alveolus and the air you inhale is that air in an alveolus enriches blood in adjacent capillaries, while the air you inhale enriches the lungs. Another difference is that the air you inhale is the product your body needs to sustain life, while the air in an alveolus will be exhaled as a harmful by-product of respiration.
State two differences between the air in the alveolus and the air which is breathed in.
When you breathe in oxygen it fills your red blood cells with oxygen (O2) rich blood. The air we breathe in traveled down our trachea and split into to branches called bronchioles, like a tree, where the trachea is the trunk and the bronchioles are the large thick branches. As the oxygen rich blood travels through the bronchioles there are thousands and thousands and tiny little "branches" called bronchiolies that then take in the cells with the healty blood. At the end of every bronchiolie there are little round "pods" surrounded by cappillaries.
As the good blood moves out of the alveolies and into the bloodstream, or the process of Diffussion, the blood coming back from the body that deposited all the oxygen to its proper places; such as organs, skin, toes and hair, the cells with oxygen poor blood move back into the alveolie through Osmosis and that is what we breathe out in the form on Carbon Dioxide.
Remember also that "air" is composed of many different parts. Oxygen is the important part for gas transfer, carbon dioxide is exhaled as a waste product, and the bulk of the colorless gas solution we breathe is nitrogen, which is inert and is not exchanged in the lungs to any great extent. Therefore, #5 is correct: the main difference is that air breathed in has a higher oxygen content than the air remaining in the alveoli.
The answers above seem to be losing focus. The alveoli are the parts of the lung where oxygen is removed from the air that has been breathed in and replaced by carbon dioxide to be exhaled. Therefore the key difference is in the content of what is breathed in and then exhaled.
I would have to agree with Vangoghfan. One main difference between the air breathed in and out of the lungs is the amount of pollutants with exist in each. Given that the air exiting the body has been filtered, it would contain far less contaminants than air taken into the body.
The air breathed into the lung can obviously be contaminated by pollutants, especially by cigarette smoke. The air breathed out would be less contaminated, if contaminated at all, because most or all of the contaminants would have been absorbed by the lungs.
When you breathe, air enters your nostrils and travels through your respirtatory system where if finally ends up in clusters of alveoli in the lungs. Some of the oxygen you breathe in is absorbed by the alveoli, and some of the carbon dioxide in your blood diffuses out through the alveoli. So the air that is breathed in is oxygen, and the air that is breated out is carbon dioxide. That is one difference.