During lung gas exchange, oxygen molecules move toward which cells?

• A. White blood cells
• B. Alveolar sacs
• C. Red blood cells
• D. Pulmonary arteries

Answer: (C)

The correct answer is red blood cells because during lung gas exchange, known as external respiration, oxygen diffuses from the alveoli into the bloodstream. The alveoli are the tiny air sacs in the lungs where gas exchange occurs, allowing oxygen to enter the blood and carbon dioxide to be expelled.

Red blood cells contain hemoglobin, a protein that binds to oxygen molecules. Once the oxygen diffuses into the blood, it is picked up by red blood cells, which transport it throughout the body. This is a crucial process as it ensures that oxygen is delivered to tissues and organs where it is needed for cellular respiration and energy production.

In contrast, while alveolar sacs are involved in gas exchange, they are not the cells that oxygen moves toward; rather, they are the structures where oxygen enters the bloodstream. White blood cells play a role in the immune response and do not participate in gas exchange. Pulmonary arteries carry deoxygenated blood away from the heart to the lungs, but they do not serve as the destination for oxygen molecules during this exchange. Therefore, red blood cells are the correct answer, as they are directly involved in the transport of oxygen after its absorption in the lungs.