Oxygen
The primary gas that humans exhale when breathing is carbon dioxide.
it not a gas it your brain
During breathing a gas is expelled.
If you wish to breed them a mate is neccessary. Otherwise a mate is not neccessary.
Oxygen
Gas exchanges
oxygen
gas is fart and oxygen is for breathing.
death
oxygen
Injury at the alveolar level impairs gas exchange in the lungs. That change in gas exchange in turn would case ineffective breathing.
if neccessary