Carrier Protein Saturation in Facilitated Diffusion

Steps:

• Identify the graph as showing facilitated diffusion kinetics for glucose transport.
• Note the plateau represents the maximum transport rate (Vmax).
• Recognize that Vmax occurs when all carrier proteins are fully occupied.
• Conclude the plateau is due to saturation of available carriers.

Why A is correct:

• In facilitated diffusion, the transport rate follows Michaelis-Menten kinetics, where saturation (all carriers bound) limits the rate to Vmax regardless of higher substrate concentration.

Why the others are wrong:

• B: Denaturation would eliminate transport entirely, not create a sustained plateau.
• C: Equal concentrations indicate equilibrium with zero net transport, not a maximum rate plateau.
• D: Glucose entry via carriers (e.g., GLUT proteins) is passive facilitated diffusion, not ATP-dependent active transport.

Final answer: A