Which organ is primarily responsible for oxygenating blood?

The primary organ responsible for oxygenating blood is the lungs. This process occurs through the alveoli, tiny air sacs in the lungs where gas exchange takes place. When a person inhales, oxygen is absorbed into the bloodstream through the walls of these alveoli. At the same time, carbon dioxide—a waste product of metabolism—is transferred from the blood into the alveoli to be exhaled. This vital exchange ensures that oxygen is continuously supplied to the body while removing carbon dioxide, maintaining healthy physiological function.

The heart, while crucial for circulating the oxygenated blood throughout the body, does not perform the oxygenation itself. The liver and kidneys serve important roles in metabolism and waste filtration, respectively, but they do not directly contribute to the process of oxygenating blood. Hence, the lungs are the correct answer for this question.