Final answer:
Increasing the thickness of the plasma membrane decreases the rate of net diffusion as it extends the distance molecules must travel, thus slowing down their movement.
Step-by-step explanation:
The effect of increasing the distance (thickness) on the rate of net diffusion is that it decreases. This is because diffusion involves molecules moving from an area of high concentration to an area of low concentration, and the thickness of the plasma membrane serves as a barrier to this process. When the membrane is thicker, it takes longer for molecules to pass through, thus slowing down the rate of diffusion.
Several factors can influence diffusion rates including temperature, solvent density, and the extent of the concentration gradient. Higher temperatures will increase the diffusion rate by providing more energy to the molecules, causing them to move faster. Alternatively, increased solvent density can decrease the diffusion rate as it makes the medium denser and more difficult for molecules to pass through.
The greater the difference in concentration, known as the concentration gradient, the more rapid the diffusion. Once the system approaches equilibrium, where concentrations are equal, the rate of diffusion slows down significantly. In summary, a thicker membrane slows down diffusion due to reduced molecule mobility.