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Multiple Choice
Which statement best describes what happens to the carbon dioxide ($\mathrm{CO_2}$) produced by humans during cellular respiration?
A
It is used directly by cells to produce ATP.
B
It is exhaled as a waste product through the lungs.
C
It is converted into glucose and stored in the liver.
D
It is absorbed by the kidneys and excreted in urine.
Verified step by step guidance
1
Step 1: Begin by understanding the process of cellular respiration. Cellular respiration is the metabolic pathway where cells convert glucose and oxygen into energy (ATP), water, and carbon dioxide ($\mathrm{CO_2}$). Carbon dioxide is a byproduct of this process.
Step 2: Recognize the role of carbon dioxide ($\mathrm{CO_2}$) in the body. It is not used directly by cells to produce ATP, as ATP is generated during the earlier stages of cellular respiration, specifically in glycolysis, the Krebs cycle, and oxidative phosphorylation.
Step 3: Eliminate incorrect options. Carbon dioxide ($\mathrm{CO_2}$) is not converted into glucose and stored in the liver. Glucose is synthesized during gluconeogenesis, but this process does not involve carbon dioxide as a substrate. Similarly, carbon dioxide is not absorbed by the kidneys and excreted in urine; the kidneys primarily filter nitrogenous waste products like urea.
Step 4: Understand the exhalation process. Carbon dioxide ($\mathrm{CO_2}$) is transported from cells to the lungs via the bloodstream. It is dissolved in the blood as bicarbonate ions ($\mathrm{HCO_3^-}$) or bound to hemoglobin. In the lungs, it is released and exhaled as a waste product.
Step 5: Conclude that the correct answer is: 'It is exhaled as a waste product through the lungs.' This aligns with the physiological process of removing carbon dioxide produced during cellular respiration.