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 that you can smell it everywhere.
or if you put some food colouring in a beaker of water, it will diffuse through the water until the whole glass is the same colour. 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 you 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 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 we'll get a higher rate of diffusion across the 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.