Explain in detail the need for ventilation systems in a multicellular organism e. g. (Human)

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.