Which best describes carbon dioxide’s path out of the body during cellular respiration?

• A. It diffuses from cells into the bloodstream, is transported to the lungs, and is exhaled.
• B. It is absorbed by the kidneys and excreted in urine.
• C. It is converted into glucose in the liver and stored for later use.
• D. It is broken down into oxygen and carbon in the mitochondria.

Answer: (A)

Verified step by step guidance

1. Understand the process of cellular respiration: Cellular respiration is the process by which cells produce energy (ATP) by breaking down glucose. During this process, carbon dioxide (CO₂) is generated as a waste product in the mitochondria.
2. Learn how carbon dioxide exits the cells: CO₂ diffuses out of the cells into the surrounding capillaries because of the concentration gradient (higher concentration of CO₂ in cells compared to the bloodstream).
3. Understand how CO₂ is transported in the bloodstream: Once in the bloodstream, CO₂ is transported primarily in three forms: dissolved in plasma, bound to hemoglobin, or as bicarbonate ions (HCO₃⁻). The majority is converted to bicarbonate ions through the reaction: CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻.
4. Learn how CO₂ reaches the lungs: The blood carries CO₂ to the lungs, where it diffuses into the alveoli (tiny air sacs in the lungs) due to the concentration gradient (higher concentration of CO₂ in the blood compared to the alveoli).
5. Understand the final step: CO₂ is exhaled from the lungs into the external environment during the process of breathing. This completes the path of CO₂ out of the body.