there are so many gases in the atmosphere.then why do we inhale ONLY OXYGEN.?

Answer 1

We actually inhale all the gasses.
Inhaling is just the action of filling our lungs with the available gas. If we somehow had a magic filter that stopped all other gasses, it would be like wearing a permanent gas-mask, and we would never be poisoned by toxic gasses like carbon monoxide.

We only actually *use* oxygen, because it is a substrate of the process of respiration, which is how we actually generate energy. We absorb the oxygen from inhaled air through our lungs and into the blood, where it binds the haemoglobin in our red blood cells, and is therefore carried around the body.
In the body, the glucose from our food is broken down in a series of reactions that end with the addition of oxygen, and generate CO2 (carbon dioxide) and H2O (water). The CO2 is carried back through our bloodstream, and we breathe it out from our lungs.

Answer 2

We inhale all of the gases but at 1 atmosphere we only absorb the oxygen in any great quantity.
At high pressure we retain the nitrogen as well which is the danger to divers as the gas bubbles out of their blood when they come up to fast.

Answer 3

well technically we inhale all of the gases, but exhale all of the others except for some oxygen. oxygen is the only gas used in human metabolism (it is an energy source used to oxidise carbohydrates and sugars). some bacteria use gases in their metabolism, for example hydrogen sulfide.

Answer 4

We don't, we inhale all that good stuff, Nitrogen Carbon Dioxide and Oxygen, but our body only uses Oxygen.

Plants:
Intake CD (Carbon Dioxide), exhale Oxygen

Humans/Animals:
Inhale Oxygen and CD and everything else and exhale CD and everything else.

I learned this in grade school, like what 2nd grade?