Final answer:
Decreasing permeability slows the diffusion rate of substance C2 across a membrane, leading to a more gradual change in concentration over time on a C2 vs. time graph.
Step-by-step explanation:
When discussing the effects of permeability on diffusion, referring to a C2 versus time graph implies monitoring the concentration of a substance over time as it diffuses across a membrane. If you decrease permeability (either by reducing the number of channels or by making the membrane less permeable to diffusion), the rate at which substance C2 crosses the membrane will be slower. This change will be reflected on the graph as a more gradual increase or decrease in the concentration of C2 over time, depending on whether C2 is entering or leaving the system. Essentially, a decrease in permeability leads to a decrease in the diffusion rate, which means it will take a longer time for the substance C2 to reach equilibrium across the membrane.