What sets the rate of diffusion?

Simple diffusion of a small non-polar molecule (O₂, CO₂) · net movement is always down the gradient · relative rate = surface area × concentration difference ÷ diffusion distance

Set up the exchange surface

Concentration outside 80

Concentration inside 40

Surface area ×2.0

Diffusion distance (thickness) ×2.0

Custom set-up. Try a preset, or change one factor at a time.

Across the membrane

Yellow band = exchange surface: its height shows the surface area, its width shows the diffusion distance. Grey = no exchange.

Readings

Concentration difference
Net movement
Relative rate
Rate vs before this change

Change one factor at a time and watch the rate.

A steeper gradient diffuses faster
A thicker barrier diffuses slower
No gradient, no net movement