Diffusion

• Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.
• Diffusion can happen in both gases and liquids, for example, if you spray perfume it quickly diffuses across the whole room so you can smell it everywhere or if you put some food coloring in a beaker of water it will diffuse through the water until the whole glass is the same color.
• Diffusion can also take place through some materials such as cell membranes, for example, if you have the inside of a cell on one side and the outside of the cell on the other, and this barrier in between is a cell membrane, then only some molecules are able to diffuse through them, generally only very small molecules that are dissolved in the fluid inside or outside the cell can diffuse through, whereas larger molecules can't fit through the membrane because they're too big.
• Diffusion is a passive process that doesn't require any energy from the cell, it's just the random movement of the particles themselves that results in diffusion.
• The concentration gradient is the difference in concentration between two places, for example, if there are more particles on the left side than the right side, the particles will diffuse from left to right, however, the particles in the top box will diffuse across to the right more quickly because there's a bigger difference in the concentrations on either side or in other words there's a bigger concentration gradient.
• The larger the concentration gradient between two places, the higher the rate of diffusion will be.
• Temperature is important because higher temperatures give the particles more energy and this means that all the particles will move around faster and so overall they'll diffuse more quickly, a higher temperature means a higher rate of diffusion.
• The surface area is the other factor that affects the rate of diffusion, the larger the surface area, the higher the rate of diffusion, for example, if we have these two boxes, they both have the same volume but the bottom one has a much larger surface area, this means that a lot more particles can fit around its surface and so at any point in time more particles could be diffusing in and out at once, resulting in a higher rate of diffusion across a larger surface area.