What gas is essential for life and circulates through the blood after being inhaled?

• A. Carbon Dioxide
• B. Hydrogen
• C. Nitrogen
• D. Oxygen

Answer: (D)

Oxygen is essential for life because it plays a crucial role in cellular respiration, the process by which cells produce energy. When we inhale, oxygen enters the lungs and diffuses through the alveoli into the bloodstream. Once in the bloodstream, it binds to hemoglobin in red blood cells and is transported throughout the body to various tissues and organs.

Cells utilize oxygen to convert glucose and other nutrients into adenosine triphosphate (ATP), the energy currency of the cell. This process is vital for sustaining all bodily functions and maintaining life. Without a sufficient supply of oxygen, the body's cells cannot perform effectively, leading to impaired organ function and ultimately, if not rectified, death.

The other gases mentioned do not provide the same life-sustaining benefits. Carbon dioxide is a byproduct of cellular respiration that needs to be expelled from the body. Hydrogen is not typically involved in the immediate respiratory process for energy production, and nitrogen, while an abundant gas in the air we breathe, is largely inert and does not play a direct role in metabolic processes. Thus, oxygen is the critical gas that supports life by enabling the necessary biochemical reactions for energy production.