Which of the following processes causes most of the carbon dioxide from the blood to move into the alveoli?
A.
Passive transport using carrier proteins
B.
Conversion to carbon monoxide
C.
Active transport using energy
D.
Diffusion down a concentration gradient
The Correct Answer and Explanation is:
The correct answer is D. Diffusion down a concentration gradient.
Explanation:
The transfer of carbon dioxide (CO₂) from the blood to the alveoli in the lungs primarily occurs through the process of diffusion. This is a passive transport mechanism that relies on the natural movement of molecules from areas of higher concentration to areas of lower concentration.
In the body, CO₂ is produced as a waste product of cellular metabolism. It is transported in the blood in three main forms: dissolved in plasma, bound to hemoglobin, and as bicarbonate ions (HCO₃⁻). When blood reaches the lungs, the concentration of CO₂ is significantly higher in the blood than in the alveolar air. As a result, CO₂ diffuses from the capillaries surrounding the alveoli, where its concentration is elevated, into the alveoli, where its concentration is lower. This process continues until equilibrium is reached.
Diffusion is a crucial mechanism because it does not require energy expenditure, making it an efficient way for gases to move across the alveolar-capillary membrane. The thin walls of the alveoli facilitate this gas exchange, allowing CO₂ to be eliminated from the body effectively during exhalation.
The other options presented are not applicable to this process:
- A. Passive transport using carrier proteins: While some molecules utilize carrier proteins for transport, CO₂ primarily diffuses freely due to its small size and solubility in plasma.
- B. Conversion to carbon monoxide: This is not relevant to normal respiratory function; CO₂ does not convert to carbon monoxide during gas exchange.
- C. Active transport using energy: Active transport would involve moving CO₂ against its concentration gradient, which is not how gas exchange occurs in the lungs.
In conclusion, the movement of CO₂ from blood to alveoli is best described by diffusion down a concentration gradient, allowing for efficient gas exchange essential for maintaining homeostasis.