So when we talk about passive
processes, again, there's three major ways
that we're going to go
through these processes.
Again, in a passive process, we're
moving down the concentration gradient
or from an area of high concentration
to an area of low concentration.
So this can be performed
in multiple ways.
In simple diffusion, non-polar, small uncharged molecules
are able to simply just pass through the membrane.
Examples of things that would fall under
this category include things like oxygen
which is able to just passively
go through the membrane.
If something cannot just pass through
the membrane because it is too polar
or too highly charged, then we need help.
And that's when we use
our facilitated diffusion.
And so in this way, we use either
channel proteins or carrier proteins.
In channel-mediated diffusion, these channels allow
certain substances to move across the membrane.
These channels are usually specific for a substance and
are not going to allow just anything to pass through.
Examples of channel proteins include things
like aquaporins which are specific for water
and allow water to go inside and outside of
the cell as well as certain ion channels
which are important for our nerves and our
muscles and lots of other cells in the body.
And then the third type of
diffusion is carrier-mediated diffusion
which involves the use of a carrier protein
and much like the channel mediated diffusion,
we're going to move substances
down the concentration gradient
using a protein that will change shape in order
to move things from one side to the other.