BIO156 online / summer – Ch 5 (part B): cell transport

BIO156 online / summer – Ch 5 (part B): cell transport


Okay, thanks for joining me! We are going to finish off this chapter with
a combination of voiceover presentation, traditional video, and a time lapse animation. – So, a lot going on with this last concept
of cell transport! But, it will be fun! So, we remember that the plasma membrane was
the layer that separated the inside and outside of the cell, but also played a key role in
regulating what comes in to the cell and what leaves the cell. It does this by being selective of what can
go through it. And, there are three ways how this can happen. We will start with the active transport and
talk a little bit about the basics of passive transport, but then I want to explain the
rest using a few other forms of talking to you. So, your diffusion lab would have been an
example of passive transport, but not all materials cross the membrane just that way. Sometimes, additional energy is needed. Protein pumps that are embedded into the plasma
membrane are very good examples of this. So, we move substances against their natural
concentration gradient. This means that this direction of movement
of materials would never happen normally by itself, so we must invest some energy to making
it happen. Remember our example of the books in the beginning
of this chapter. This is just like spending energy to lift
the books up in the shelf. – Energy is now stored in the way these
ions are placed against what would naturally happen. Let’s move now to talk about passive transport. This was the case with your diffusion lab. Materials move down their concentration gradient:
from high concentration to low concentration. This means that if there is a lot of something
on one side, and little on the other side, over time the amount on both sides will become
similar. Let’s look at this using one of my favorite
examples. So, if you put a drop of food coloring in
one corner of a glass full of water, eventually this coloring will spread evenly all over
the water inside the glass. And, this would hold true even if there was
a membrane within this glass, separating two sides of it. As long as the membrane is permeable to those
molecules of the food coloring, it will passively spread everywhere. The important thing to remember here is that
no energy is needed to be spent on this, it just happens by itself – passively. Let’s take this concept and look at another
example of passive transport. And this takes the previous a bit further,
so you might need to think about it a bit, initially. So, what if we now do not have a membrane
that lets the food coloring through? Yet, we know that it will want to even out
over time, so that both sides have the same concentration of this food coloring. Well, this would be something that we know
as osmosis. And, just to make our life easier, let’s
consider that most of the food coloring (the example that we used earlier) is on the right
hand side of this glass. But, some – just a tiny number of molecules
– is on the left hand side. So, this is the situation that we are starting
with. And, now, we remember that molecules need
to reach the same concentration on both sides. But, this time, the membrane does not allow
the food coloring to pass through it. This leaves us in a bit of a new situation,
doesn’t it? So, what can we do? Well, what we do is that if the food coloring
cannot move across the membrane, let’s let the water molecules move across it! And, what we will notice to happen is that
we are able to achieve a same concentration of food coloring on both sides by moving some
of the water from left to right. That worked out nicely! And, at this stage I see that students in
my face-to-face classes are usually sitting with a blank expression on their face and
tell me: ‘Well, that’s very nice and all, but how does that relate to anything that
I am planning to do as a medical professional?’ And, I tell you, it has everything to do with
it. In fact, our next video will discuss three
cases what can happen when water moves across the membrane of red blood cells. And, just as a basis for that, I ask you now:
‘Can you die of drinking too much water?’ And, the answer is: Yes, you can! In fact, this happened some time ago here
in the America, as one radio station had a competition where the listeners could win,
I believe it was one of these new consoles, like Nintendo Wii. And, all you had to do was to drink a lot
of water in a very short period of time. And, what happened was that this woman did
so, and her cells ended up bursting! How crazy is that? Well, after the next video you will know all
about how that happened. – Whoever thought of this competition clearly
must have skipped their biology classes.

Leave a Reply

Your email address will not be published. Required fields are marked *