Nutrient and gas exchange in active muscle

Steps:

• Active muscles consume oxygen for respiration, lowering its concentration in tissue fluid compared to plasma.
• Glucose is taken up by muscle cells for energy production, creating a gradient from plasma to tissue.
• Net movement follows concentration gradients via diffusion across capillary walls.
• Waste products like CO2 and lactic acid move oppositely, from tissue to plasma.

Why C is correct:

• Oxygen and glucose are depleted in muscle tissue during activity, driving net diffusion from higher plasma concentrations to lower tissue levels (Fick's law of diffusion).

Why the others are wrong:

• A: CO2 is produced in muscle and diffuses net from tissue to plasma.
• B: Both CO2 and lactic acid are muscle byproducts, moving net from tissue to plasma.
• D: Lactic acid diffuses net from tissue to plasma; oxygen moves into tissue.

Final answer: C