Nutrient and waste exchange in capillaries

Steps:

• Blood capillaries deliver essential nutrients and gases like glucose and oxygen to cells for metabolism.
• Cells release metabolic byproducts such as carbon dioxide and water back into the blood for removal.
• Review options to match incoming substances (P: glucose, oxygen) with outgoing ones (Q: carbon dioxide, water).
• Eliminate mismatches based on typical physiological transport.

Why D is correct:

• Matches cellular respiration equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O, where glucose and oxygen enter cells, and CO₂ and H₂O exit.

Why the others are wrong:

• A: Maltose is a disaccharide not directly exchanged; amino acids are proteins' building blocks, but maltose mismatches waste.
• B: Reverses directions (CO₂ and glucose aren't primarily incoming); alcohol isn't a standard cellular waste.
• C: Urea is a nitrogenous waste from blood to kidneys, not cells to blood; proteins are too large for simple capillary diffusion.

Final answer: D