Which of the following statements about carbon dioxide is true?

The statement that carbon dioxide is a waste product of metabolism is true because carbon dioxide is produced when the body metabolizes carbohydrates, fats, and proteins for energy. During cellular respiration, oxygen is used to convert these nutrients into usable energy, resulting in carbon dioxide as a byproduct. This carbon dioxide is then transported via the bloodstream to the lungs, where it is exhaled.

Understanding this process highlights the critical role carbon dioxide plays in the body’s metabolic functions. While it is essential for certain biological processes, such as maintaining the acid-base balance and stimulating respiration, it is primarily recognized as a waste product that needs to be expelled to maintain healthy physiological function.

In contrast, while carbon dioxide is essential for life in certain contexts, particularly in relation to plants that use it for photosynthesis, this characterization does not capture its role in human metabolism. Additionally, carbon dioxide is not the primary molecule for oxygen transport; that role is fulfilled by hemoglobin in red blood cells. Lastly, carbon dioxide is not harmless in all concentrations; elevated levels can lead to respiratory acidosis and other physiological disturbances, making understanding its effects critical in diving and other high-stress environments.