Capillary exchange of gases, nutrients, and fluids

Steps:

• Arrow 1 points from blood to tissue: oxygen diffuses down its concentration gradient to cells.
• Arrow 2 points from blood to tissue: water moves via osmosis due to higher hydrostatic pressure in capillaries.
• Arrow 3 points from tissue to blood: carbon dioxide diffuses down its gradient back to blood.
• Arrow 4 points from blood to tissue: glucose diffuses as a nutrient to supply cells.

Why C is correct:

• C matches diffusion gradients where oxygen and glucose move blood-to-tissue, carbon dioxide tissue-to-blood, and water follows osmotic pressure, per Fick's law of diffusion.

Why the others are wrong:

• A: Mislabels arrow 1 as carbon dioxide, which diffuses tissue-to-blood, not blood-to-tissue.
• B: Labels arrow 4 as urea, a waste product diffusing tissue-to-blood, opposite the direction.
• D: Identical to B, so incorrectly assigns urea to arrow 4.

Final answer: C