in today's video we're looking at diffusion so we're going to cover what diffusion is and how it works how it applies to cell membranes and finally the different factors that affect its rate now the key idea to this entire topic is that if molecules are left alone they'll move about randomly and this means that if we have a group of molecules all bunched up together in one place like we do here then over time they'll slowly spread out due to their random motion until they're pretty evenly distributed among all of the space that they have we call this process of spreading out diffusion and the definition that you want to remember is that diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration or in other words the particles will move from where they're all bunched up which we can think of as a high concentration of particles to where they're more spread out which we describe as a low concentration also when we use the term net movement all we mean is the movement of all of the particles considered together as a group for example if we replay our animation again we can see that because each particle is moving randomly sometimes individual particles do move closer together but overall if we consider them all as a group then they are always spreading out it's also important to know that 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 the next thing we need to look at is the idea that diffusion can also take place through some materials such as cell membranes for example let's imagine that on the left we have the inside of a cell on the right we have the outside of the cell and this barrier in between is a cell membrane we call membranes like this partially permeable which means that 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 for example things like water glucose and amino acids whereas larger molecules can't fit through the membrane because they're too big examples of these larger molecules would be things like proteins and starch another thing to point out here is diffusion is a passive process this means that it doesn't require any energy from the cell it's just the random movement of the particles themselves that results in diffusion so now that we know what diffusion is let's run through the three factors that affect the rate of diffusion the first is the concentration gradient which is just the difference in concentration between two places for example if we look at these two boxes in both cases there are more particles on the left side than the right side so 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 so to summarize this point the larger the concentration gradient between two places the higher the rate of diffusion will be the next factor is temperature which 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 so a higher temperature means a higher rate of diffusion the last factor is the surface area and the rule here is that the larger the surface area the higher the rate of diffusion to see why imagine that 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 so overall it will get a higher rate of diffusion across a larger surface area anyway that's everything for this video so if you found it helpful then please do tell your friends and teachers about us or give us a thumbs up and hit subscribe and we'll see you again soon