- [Voiceover] When molecules go across the plasma membrane,
there's more than one way for it to occur.
They can go through what's called passive transport.
In the case of passive transport, the particles moving
and the membrane itself does not need any energy.
The energy has been stored or has
already been exerted before.
So, types of transport are diffusion and osmosis.
Diffusion you might have heard of already.
Think of diffusion, you might start
thinking of someone baking cookies.
Do you have to have your head right
in the stove to smell the cookies?
No, the smell has diffused from the stove
and the oven over to where you are.
Osmosis, we'll touch on later.
Active transport, cells have to expend energy.
So, you have to put energy into the system
to make the system work.
Then there's this bulk transport.
It involves the vesicles.
What actually happens is, think about
endo and exocytosis, is the way
of moving large particles or large things back and forth.
What if they can't fit through those protein channels?
In endocytosis, E-N-D-O, you're bringing substances in.
Endo, within.
While exocytosis, E-X-O, exo, think of exit.
The substances are leaving.
Endo and exocytosis.
Does passive transport, okay, remember, no energy
at the time is moving, is all powered
by a concentration gradient.
The simple basic idea of diffusion,
a particle moving though the lipid layer.
Well, you also have simple basic diffusion
through a protein channel, but then sometimes
you have this facilitated transport.
That means you have to have transport
or carrier protein in the membrane.
Something's helping or opening a port.
Think of that smell back in the oven again.
Baking those nice chocolate chip cookies.
You can smell it in the kitchen,
but if all the windows are shut
can you smell it outside the kitchen window?
No, you shouldn't be able to.
Unless your windows have a whole lot of leaks in them.
But now, if you open that window,
and you're standing outside, would
you be able to smell the chocolate cookies?
Most likely.
That window, by opening it, you're facilitating,
or helping, the transport.
This is meant to show how particles
can move through various types of passive transport.
You can see diffusion, diffusion through channels,
and facilitated transport.
So, this idea of diffusion right though the lipid bilayer.
Particles small enough, going from
a high concentration to a low concentration.
The reason here why it goes through, from high to low,
is every system is trying to reach
what's called equilibrium.
Equilibrium is when both environments
are equal or the same.
In this particular figure, the top portion,
the blue, has a much higher concentration
of all three spheres.
The bottom part, the yellow, has
a much lower concentration.
That means this particular membrane
will have transport going across it
until you reach equilibrium of all particles.
Or, equilibrium cannot be reached, one of the two.
So, we go from high to low, right through the membrane.
We can go from high to low right
through a channel, the middle one.
The channel helps just get a little bit
easier passageway, or allows it to float through.
Well, the far right, facilitated transport.
The black sphere, this is too large to
go through the protein channel,
and definitely too large to go through the plasma membrane,
so it goes into this protein channel
which then will change shape and
release it to the inside.
So we have three different ways here.
What's not shown is the idea of osmosis
I said we'd get back to.
Osmosis works a very similar principle,
only difference is the membranes are not semi permeable.
Everything's kept inside for osmosis.
That means the only thing left to move is water.
Osmosis is the movement of water
from high to low concentration gradient.
But it's all based on the initial concentration
of the liquid, both sides.
Switching gears to active transport.
Active transport does exact opposite of passive.
You have to have ATP, which is energy.
You need to have a protein, and it's
moving in the reverse action of your passive transport.
Passive transport was high concentration to low,
active is going from a low concentration
up to a high concentration.
It's helping to reset the gradients.
So, here we have active transport.
Left hand side, letter A, you can see that
the ATP or the energy has been converted
to ADP and inorganic phosphate.
This is necessary because you have to have energy
to push against the gradient.
Notice that black sphere is going up into the blue?
There's already more of those spheres up there.
Right hand side, carrier proteins.
The carrier proteins you see enter in,
they then are all set and ready to go,
tucked in, and released on the inside, carrier proteins.
Endo and exocytosis.
Does anyone remember what the term "endo" was referring to?
Endo, or within.
Exo, or, what's also for exo?
Exo is exit, or out.
This is how you move large amount of particles
or very large particles all at the same time.
Endocytosis brings things in.
Exocytosis takes them out.
There's kind of this round robin,
something comes in, something goes out,
something goes in, something goes out.
Here are two more pictures depicting
endo and exocytosis.
The top left, which is A, is showing you endocytosis.
You can see how many particles are
being brought in at one time.
It's like a bulk delivery.
While the next one down, B, is exocytosis.
The particles are exiting.
So, the vesicles open up wide, releasing
all the particles out and allowing
itself to get reabsorbed, taken back in.