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Multiple Choice
Which of the following is NOT transferred across the alveolar membrane during gas exchange in the human lungs?
A
Water vapor ($H_2O$)
B
Oxygen ($O_2$)
C
Carbon dioxide ($CO_2$)
D
Glucose
Verified step by step guidance
1
Understand the function of the alveolar membrane: The alveolar membrane in the human lungs is responsible for gas exchange between the air in the alveoli and the blood in the capillaries. This process involves the diffusion of gases such as oxygen ($O_2$) and carbon dioxide ($CO_2$).
Recognize the role of water vapor ($H_2O$): Water vapor is also present in the lungs and can diffuse across the alveolar membrane as part of maintaining moisture and facilitating gas exchange.
Identify the substances involved in gas exchange: Oxygen ($O_2$) is transferred from the alveoli to the blood, while carbon dioxide ($CO_2$) is transferred from the blood to the alveoli to be exhaled. Water vapor ($H_2O$) can also move across the membrane.
Clarify why glucose is not transferred: Glucose is a large molecule that does not diffuse across the alveolar membrane during gas exchange. Its transport in the body occurs through the bloodstream and is regulated by other mechanisms, such as facilitated diffusion and active transport.
Conclude that glucose is the correct answer: Since glucose is not involved in the gas exchange process across the alveolar membrane, it is the substance that is NOT transferred during this process.