Nutrient and waste exchange in tissue capillaries

Steps:

• Blood delivers glucose and oxygen to cells for cellular respiration.
• Cells consume glucose and oxygen, producing carbon dioxide and water as byproducts.
• Carbon dioxide and water diffuse from cells into the capillary for transport to lungs and kidneys.
• This exchange matches the typical diagram of tissue capillary function, identifying P as glucose and oxygen, Q as carbon dioxide and water.

Why D is correct:

• Matches the cellular respiration equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O, where blood supplies reactants and removes products.

Why the others are wrong:

• A: Amino acids and maltose are not primary respiration products; maltose is a dietary sugar, not a waste.
• B: Alcohol is not produced in normal cellular respiration; glucose direction is reversed.
• C: Urea is a nitrogenous waste from protein metabolism, not respiration; proteins do not diffuse across capillaries.

Final answer: D