Membranes [4]: Active Transport (A Level Biology)

Uploaded by freeeschool on 29.09.2012

A Level Biology: Membranes 4 – Active Transport
Hi! Welcome to my fourth video on the series about Membranes. Today, we are looking at
Active Transport.
So here are some examples where Active transport is used: absorbing glucose by the small intestine
and in the kidney tubule cells; salt uptake by roots of plants; and amino uptake by fungi.
Essentially, what active transport actually is it enables you to move chemicals and molecules,
instead of down a concentration gradient, enables you to move it against it. So instead
of facilitating diffusion or osmosis, which are passive and which require no energy because
they happen down a concentration gradient, what you are actively trying to do is you
try to move something from where there is not a lot of it to a lot of it; that therefore
requires energy and ATP.
What we have here is an example of Active transport specifically with sodium ions and
so they require a carrier protein in order to do this. What you got here are sodium ions
moving from the intracellular fluids, so moving from the inside of the cell to outside. We
can, first of all, establish that outside the cell, there is a big concentration of
sodium ions. Therefore, this is why ATP is required in order to move them because it
is moving against the gradient. So what happens is the ATP is broken down and is broken down
into ADP and a phosphate group and energy is released. That energy is used to change
the shape of the carrier protein. That change in shape can therefore release the sodium
ions to the outside of the cell, hence, that’s active transport.
So we’ve looked at moving objects or molecules like sodium ions and water, but what happens
when you want to move something much larger across the membrane? Something like a protein?
For that, you would use the following processes: Endocytosis, Exocytosis and Pinocytosis. We
are going to look at those in a second.
In Endocytosis, a chemical like a protein might bind to the surface membrane and the
plasma membrane basically folds around that object or that molecule and it forms a sealed
environment inside so that you can take in a chemical like a protein into the cell and
again, without a change in the biochemistry of the cell.
Endocytosis and Pinocytosis are synonyms. They’re very similar to one another. So
for in aid of a qualification, you probably wouldn’t be expected to differentiate between
the two. Endocytosis is where you take in a substance. Exocytosis is where it is released,
hence, “exo” like exit. They use this organelle called vesicle and the vesicle is
essentially a lipid bilayer that is formed around molecules that need to be secreted
or gotten rid of. What happens is because those chemicals may actually cause damage
to the cytoplasm or will change the chemistry of the cytoplasm that is contained within
a lipid bilayer, and that is referred to as a vesicle, the vesicle will then fuse with
the plasma membrane and then it will enable the chemicals or the molecules to be secreted
without ever coming into contact with the cytoplasm.
In summary, Active transport is the movement of substances across a membrane via a carrier
protein against a gradient and therefore requiring ATP and is not passive and is active. Exocytosis
is the release of larger chemicals from the cells, so “exo” get rid like exit. Endo
is absorption of larger chemicals. Both processes are used in an organelle called a vesicle
which is a membrane-bound organelle and is used to transport things that are inside the
cell or outside.
[end of audio – 03:57] A Level Biology: Membranes 4 – Active Transport