6. The Membrane
Introduction to Membrane Transport
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In this video we're going to begin our introduction to membrane transport. And so it's important to know that biological membranes are actually semi permeable. Which really just means that biological membranes can act as barriers to essentially prevent diffusion of some molecules across the membrane. Now it's also important to note that the term semi permeable is synonymous with the term selectively permeable. And so selectively permeable and semi permeable really just mean the same thing. And again, all it's saying is that membranes are really, really picky about what types of molecules they allow to cross the membrane. And so the term permeable is a term that actually means how penetratable something is. And the term selectively of course just means picky. It is going to select the specific types of molecules that are able to cross the membrane freely. And again the root semi is a root that means partial and so semi permeable just means partially penetratable. And so really all of this is just saying that, biological membranes are selectively permeable or semi permeable meaning that they're super picky about what types of molecules can cross and what types of molecules cannot cross. And so if we take a look at our image down below we'll be able to see an example of a selectively permeable biological membrane. And so notice in this cartoon image here in the middle we're showing you our biological membrane which we know is a semi permeable membrane or a selectively permeable membrane. And again, all this means is that it's really picky about what it allows to cross the membrane. So notice on the left hand side we're showing you 2 molecules, a sodium ion and an oxygen molecule or an O2 molecule. And notice that only the o two molecule in this cartoon is able to cross the membrane freely and the sodium ion is not able to cross the membrane. And again this is because of the properties of these molecules and we'll be able to talk more about what exact properties do these molecules need to have in order to be able to cross the membrane freely in our next lesson video. But here in this cartoon notice that the membrane here is saying, excuse me, do you have an appointment? And when it's talking to you, it's talking about the sodium ion. And the sodium ion does not have an appointment in this cartoon. So, he's saying this isn't fair stupid barrier, I'm not able to get through. Whereas the oxygen molecule here is able to get through and he's saying we have an appointment, let's go and it's able to cross. And so this is just a silly cartoon, but hopefully it drives home the point of how biological membranes are semi permeable. And so this concludes this video and I'll see you all in our next one.
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