Question

Humans are dependent on the air for

• A. Circulation
• B. All of the above
  
• C. Nutrition
• D. Respiration
  

Answer 1

The correct option is D Respiration


Air
Air is a mixture of gases containing $21\%$ oxygen, $78\%$ nitrogen, $0.9\%$ argon, $0.04\%$ carbon dioxide and trace amounts of other gases and water vapor.

Nutrition
Nutrition is the physiological and biochemical process of obtaining nutrients in the form of food by an organism.
It occurs in $5$ steps: ingestion, digestion, absorption, assimilation and egestion.
It is not dependent on the air directly.

Respiration
Respiration is the biochemical process to produce energy in the form of ATP by the oxidation of respiratory substrates such as glucose, fats, and proteins.
It involves oxygen gas as a final electron acceptor to completely oxidise respiratory substances.
Thus, air is required by humans for respiration.

Circulation
Circulation is the physiological process of transporting nutrients, gases such as oxygen, carbon dioxide, hormones, vitamins, wastes through blood to all parts of the body..
It is not an oxygen dependent process.