Multiple Choice
Which of the following represents the balanced chemical equation for cellular respiration?
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8. Respiration
Introduction to Cellular Respiration
Multiple Choice
Most carbon dioxide is carried from the body tissues to the lungs _____.
A
as bicarbonate ions (\(\mathrm{HCO_3^-}\)) dissolved in plasma
B
dissolved directly as CO\(_2\) gas in plasma
C
bound to hemoglobin as carbaminohemoglobin
D
attached to oxygen molecules in red blood cells
Verified step by step guidance1
Understand the context: Carbon dioxide (CO\(_2\)) is a waste product of cellular respiration and must be transported from body tissues to the lungs for exhalation. The question asks about the primary method of CO\(_2\) transport in the blood.
Recall the three main ways CO\(_2\) is transported in the blood: (1) as bicarbonate ions (\(\mathrm{HCO_3^-}\)) dissolved in plasma, (2) bound to hemoglobin as carbaminohemoglobin, and (3) dissolved directly as CO\(_2\) gas in plasma.
Focus on the most common method: The majority of CO\(_2\) is converted into bicarbonate ions (\(\mathrm{HCO_3^-}\)) through a reaction catalyzed by the enzyme carbonic anhydrase. This reaction occurs in red blood cells and can be represented as: \[ \mathrm{CO_2 + H_2O \leftrightarrow H_2CO_3 \leftrightarrow H^+ + HCO_3^-} \]
Understand the role of plasma: Once bicarbonate ions are formed, they are transported in the plasma. This is the primary method of CO\(_2\) transport, accounting for about 70% of the total CO\(_2\) carried in the blood.
Review the other options: (1) CO\(_2\) bound to hemoglobin as carbaminohemoglobin accounts for about 20-23% of CO\(_2\) transport. (2) CO\(_2\) dissolved directly in plasma as a gas accounts for only about 7-10%. (3) CO\(_2\) is not attached to oxygen molecules in red blood cells, so this option is incorrect.
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