The multi-cellular organism like the humans requires ventilation
to remain alive. The humans take in oxygen from the air for cell respiration
and breathe out carbon dioxide as a waste product. The humans breathe in air through
the mouth or nose. This air reaches the bronchi of the humans through the
trachea. From the bronchi the air passes through several bronchioles to the
alveoli. Alveoli are very tiny membranous sacs from where the oxygen present in
the air diffuses in the blood. The waste carbon dioxide diffuses in the air of
the alveoli and passes out.
