What happens to the oxygen inhaled into the lungs?

The reason why the option about oxygen entering the bloodstream is correct relates to the role of the alveoli in the respiratory system. When you inhale, oxygen-filled air reaches the alveoli, which are tiny air sacs in the lungs. Here, diffusion occurs—oxygen moves across the thin walls of the alveoli and directly into the surrounding capillaries. This process of oxygen entering the bloodstream is crucial because it allows oxygen to be transported throughout the body to the tissues and organs that need it for cellular respiration and energy production.

The body's efficient system ensures that oxygen, rather than being stored in the lungs or expelled unnecessarily, is utilized effectively to support metabolic processes. This is why the understanding of oxygen's path from the inhaled air to the bloodstream is essential for comprehending how the respiratory and circulatory systems work together to sustain life.