Question

Which among the following is not a step of human respiration?

• A. Pulmonary ventilation
• B. Diffusion of $O_2$ and $C{O}_2$ between blood and tissues
• C. Transport of gases by blood
• D. Utilisation of $C{O}_2$ by cells for catabolic reactions

Answer 1

The correct option is D Utilisation of $C{O}_2$ by cells for catabolic reactions

Respiration is an enzymatically controlled catabolic process wherein stepwise oxidative breakdown of food occurs inside living cells. This oxidative breakdown releases energy which is subsequently utilised in ATP synthesis. Therefore, oxygen and not carbon dioxide is utilised by cells for these catabolic reactions.
However, pulmonary ventilation, also called as breathing, transport of the gases like $O_2$ and $C{O}_2$ as well as their diffusion between blood and tissues are the steps involved in respiratory system.