3. Plasma membrane
• The plasma membrane is the boundary between the cell
and its environment.
• It regulates what enters and exits the cell.
• Cells must maintain an appropriate amount of molecules
to function inside them.
• They must also have a way to keep things out or to allow
things to enter.
• This is the job of the plasma membrane.
4. • The plasma membrane is
like the guard at a gated
community.
• The guard must inspect
those who enter and those
who leave to make sure
that only the people and
things needed in the
community are there.
5. Plasma Membrane Structure
• The plasma membrane is composed of a phospholipid
bilayer, which is two layers of phospholipids back-to-
back.
• Phospholipids are lipids with a phosphate group
attached to them.
• The phospholipids have one head and two tails.
• The head is polar and hydrophilic, or water-loving.
• The tails are nonpolar and hydrophobic, or water-fearing.
6. • Since water is the key
component of living
organisms, both inside
and outside of the cell,
this causes the
phospholipids to line up in
two layers with the heads
pointing outward and the
tails hidden in the middle.
7. • Located all throughout the surface of the plasma
membrane are cholesterol molecules.
• These molecules help stabilize the phospholipids and
keep them in position.
• The plasma membrane is also dotted with proteins.
• Some of the proteins are peripheral proteins that only go
halfway through the membrane, while others are integral
proteins that go entirely through the membrane.
• These proteins serve as channels to allow the molecules
to enter and leave the cell.
8. Function of the Plasma Membrane of a
Cell
• You are comfortable in your house largely because the
thermostat maintains the temperature within a certain
range regardless of what is happening outside.
• Similarly, all living cells must maintain a balance
regardless of external or internal conditions.
• This includes regulating what can enter and exit the
cell.
• The plasma membrane serves as a gateway to allow or
block the entry or exit of materials.
