(Choices A, B, C, D)
These other factors are important for determining the rate of diffusion (ie, slope of the line), but would not explain the flattening of the curve in line 1 (which is best accounted for by saturation of a protein carrier). In general, the rate of diffusion increases with:
• Higher concentration gradients across the membrane
• Lower molecular weight
• Larger diffusion surface area
• Thinner membrane thickness
For molecules that move through the membrane via simple diffusion, the degree of lipophilicity is also important; molecules with a high oil-water partition coefficient are more easily able to cross the membrane and will diffuse faster.