In this video, we're going to talk about simple and facilitated diffusion. Both simple diffusion and facilitated diffusion are types of passive transport, which means that the transport across the membrane occurs passively without any energy input whatsoever. There is absolutely no energy involved with passive transport, and that means there's no energy involved with either simple or facilitated diffusion. Recall from our previous lesson videos that the reason passive transport requires no energy is because molecules are transported down their concentration gradients from areas of high concentration down to areas of low concentration, and that's why no energy is required.
Now, simple diffusion, as its name implies, is pretty simple. It involves the direct diffusion of small uncharged molecules directly through the cell membrane, squeezing their way between the phospholipids to get from one side of the membrane to the other side of the membrane down its concentration gradient. Facilitated diffusion, on the other hand, typically transports charged molecules. As its name implies, facilitated diffusion is facilitated by a transport protein. So, facilitated diffusion requires facilitation by a transport protein, whereas simple diffusion does not require any facilitation whatsoever.
Let's take a look at our image down below to get a better understanding of this. Notice that over here on the left-hand side, we're showing you a snippet of our map where you can see that passive transport, which requires absolutely no energy input whatsoever, includes both simple diffusion and facilitated diffusion. Simple diffusion is straightforward, requires no facilitation from a protein, so no protein is involved with simple diffusion. Whereas with facilitated diffusion, the transportation does involve a transport protein, and the transport protein is what facilitates this diffusion.
So let's take a look at our image over here, to get a better understanding of this. On this half of the image, we're showing you simple diffusion, which allows small uncharged molecules to simply diffuse directly through the membrane. These molecules are uncharged and small enough to be able to squeeze their way between the phospholipids and get to the other side of the membrane from an area of high concentration down to an area of low concentration. And because it's going from high concentration to low concentration down the concentration gradient, that is why no energy is required for this type of transport, simple diffusion.
Now, over here on the right-hand side of this image, notice that we're showing you facilitated diffusion. Facilitated diffusion also transports molecules down their concentration gradients from an area of high to an area of low concentration, and no energy is needed for facilitated diffusion. The difference is that facilitated diffusion mainly transports ions, or in other words, charged molecules, whereas simple diffusion will only occur with small uncharged molecules, not with ions. If ions want to get to the other side of the membrane, then they're going to need some facilitation by a transport protein. This protein, embedded in the membrane, creates a channel, basically a tunnel, that allows these ions, these charged molecules, to diffuse down their concentration gradients across the membrane. A protein is involved, but no energy is needed because the molecules move from high concentration to low concentration.
This concludes our introduction to simple and facilitated diffusion, and we'll learn more about these processes as we move forward in our course. I'll see you in our next video.
