Agar Cube Diffusion

We use coloured agar cubes to see how different shapes change the rate of diffusion. The cubes are made using sodium hydroxide and phenolphthalein indicator to give them a pink colour. When these are added to hydrochloric acid, the colour fades as the acid diffuses through the cube. We see how the shape affects the speed of this process. Biology - Cells And DNA - Learning Points. Diffusion is an extremely important process, as it controls the movement of substances into and out of cells. The rate of diffusion is affected by various factors. The rate of diffusion is dependent on an object's surface area relative to its volume - known as the surface area to volume ratio (surface area:volume). Cell shapes are adapted to facilitate diffusion. Plant and animal organs are adapted to facilitate diffusion. A Twig Experiment Film. Let students experience real experiments in lab conditions anywhere, from setup, method all the way through to analysis and real-world application.