Simple and Facilitated Diffusion - Video Tutorials & Practice Problems
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1
concept
Simple and Facilitated Diffusion
Video duration:
5m
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Video transcript
In this video we're going to differentiate between simple and facilitated diffusion. And so simple diffusion and facilitated diffusion are both types of passive transport which you might recall from our previous lesson videos just means that the transport of the molecules across the membrane occurs passively with no energy input and so no energy is needed. And again recall from our previous lesson videos that the reason no energy is needed for passive transport is because molecules are being transported across the membrane down or with their concentration gradients from areas of high concentration down to areas of low concentration which is the natural tendency for molecules to diffuse. And so this will be true for both simple and facilitated diffusion. Now, simple diffusion as its name implies is going to be simple and direct diffusion of small uncharged molecules directly through the cell membrane without any facilitation from a membrane protein. Now on the other hand, facilitated diffusion is defined as non energetic diffusion and the non energetic just means that no energy is involved because it's a type of passive transport. And instead of, transporting uncharged molecules like simple diffusion, facilitated diffusion will typically transport charged molecules that either have a positive or a negative net charge. And these charged molecules you might recall are not able to directly diffuse across the membrane. And so these charged molecules require facilitation and they require a facilitation by a transport protein. And so really the biggest difference between facilitated diffusion and simple diffusion is that facilitated diffusion utilizes a transport protein to facilitate the transport, whereas simple diffusion does not utilize a transport protein. And so if we take a look at our image down below we can clear up some of these ideas and differentiate further between simple and facilitated diffusion. So notice on the left hand side over here we're showing you a little snippet of our map of the lesson on membrane transport. And so here we're showing you passive transport and how passive transport absolutely requires no input of energy. And again, there are 2 types of passive transport that we're discussing here, which includes simple diffusion and facilitated diffusion. Now the biggest difference between simple and facilitated diffusion once again is that simple diffusion requires absolutely no facilitation from a membrane protein. So there's no protein it of molecules that usually can't cross the membrane, such as charged molecules. And so if we look at this image over here on the left hand side, notice we're showing you an example of simple diffusion which is going to allow small uncharged molecules to directly diffuse across the membrane without any facilitation from a membrane protein and the molecules are gonna always diffuse from an area of high concentration towards an area of low concentration across the membrane. And again this is what makes this a passive process that requires no energy input. But again there's no membrane protein involved with simple diffusion. Now on the right hand side of the image we're showing you an example of facilitated diffusion and with facilitated diffusion what you'll notice is that it does indeed utilize this membrane protein that you see embedded in the membrane. And it is still going to allow molecules to diffuse from high concentration towards an area of low concentration across the membrane. Notice there's low concentration here, high concentration here. And usually these molecules are going to be ions, or in other words charged molecules. And so these charged molecules, again they do not have a natural tendency to diffuse across the membrane without facilitation. So they can't get across the membrane unless there is facilitation by a membrane protein. And so facilitated diffusion is going to allow for charged ions and molecules to diffuse across the membrane again from an area of high concentration to an area of low concentration. So still no energy is needed and it is still a passive process. And so this here concludes our brief lesson on simple and facilitated diffusion and we'll be able to get some practice applying these concepts and learn more about membrane transport as we move forward. So I'll see you all in our next video.
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Problem
Problem
Which of the following processes includes all of the others?
A
Osmosis
B
Facilitated diffusion
C
Passive transport
D
Transport of an ion down its electrochemical gradient
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Problem
Problem
The difference between simple and facilitated diffusion is that facilitated diffusion:
A
Requires a protein transporter.
B
Moves molecules against their concentration gradient.
C
Requires energy.
D
Freely diffuses molecules against their concentration gradient.
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concept
Transport Proteins of Facilitated Diffusion
Video duration:
4m
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Video transcript
So now that we know from our last lesson video that facilitated diffusion requires transport proteins, in this video, we're going to talk about some of the transport proteins of facilitated diffusion. And really there are 2 main types of transport proteins involved in facilitated diffusion. And we have those 2 numbered down below, number 1 and number 2. And so the first type of transport protein involved in facilitated diffusion are the porins, otherwise known as channels. And so as their name implies, porins and channels, they're going to form an obvious membrane spanning tunnel that will allow molecules to move across the membrane by traveling through the tunnel that these porens or channels create. And so porens implies the word por, and por is like a hole or like a tunnel. And channels, once again, are basically like tunnels as well. Now aquaporins are specifically used to transport water molecules across or through the cell membrane, essentially facilitating osmosis. So that osmosis, the diffusion of water across a semipermeable membrane, can occur at a faster rate, thanks to the aquaporins. Now the second type of transport protein involved in facilitated diffusion are the transporters, otherwise known as carriers. Now the transporters or carriers, unlike the ports and channels, they do not form an obvious membrane spanning tunnel. Instead, the transporters or carriers, they're only open on one side of the membrane at a time, and they must undergo conformational changes in order to move molecules across the membrane. So let's take a look at our image down below to get a better understanding of these ideas. So notice on the left hand side over here what we're showing you are porins and channels. And so notice that porins and channels, they're going to create a membrane spanning tunnel that is basically going to allow molecules to move through the membrane, through the tunnel, and cross to the other side. Now, aquaporins are specifically porens that allow water molecules to diffuse across the membrane at faster rates, essentially allowing osmosis to occur faster. And you can see that channels, like ion channels like this, can allow ions that, have charges like a a positive charge, for example, to move through the tunnel here and get to the other side of the membrane. And so over here, what we see is that there are obvious membrane spanning tunnels, and so there's an opening on both sides of the membrane. Now when we take a look at the right hand side of the image over here, notice that we're showing you transporters or carrier proteins. When you look at these, notice that it does not form an obvious membrane spanning tunnel like these do over here. Instead, the transporters are only open to one side of the membrane at a time. And so in order to transport these molecules from one side of the membrane to the other side of the membrane, this transporter or carrier protein must undergo a conformational change. And so notice that over here, the transporter or carrier has undergone a confirmational change that can allow the molecule on the inside to be released to the other side of the membrane. And so, what you'll notice is that, here, the transporter or carrier protein is only open to one side of the membrane, which is over here, and it's closed on this side of the membrane. And so, transporters or carriers are only gonna be open to one side of the membrane at a time, and it's only after the conformational change occurs where they can change their shape and, be open on the other side of the membrane. And so both of these are types of transport proteins involved in facilitated diffusion, allowing molecules to be transported down their concentration gradients passively without any energy input. And so this here concludes our lesson on this, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.
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Problem
Problem
Which of the following does not accurately describe a channel or a carrier?
A
Channel – open to both sides of the membrane simultaneously.
B
Carrier – open to one side of the membrane at a time.
C
Carrier – requires a conformation change to complete function.
D
Channel – not selective for molecules that move through it.
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Problem
Problem
Which type(s) of molecules cannot enter/exit the cell via simple diffusion and require facilitated diffusion?