Topic: The cell membrane
 How
is a window screen similar to
a cell membrane?
Answer the following questions to
find out...
1. What are some things that can pass through
a window screen?
2. What are some things that cannot pass
through a window screen? Why is it important
to keep these things from moving through
the screen?
3. The cell is surrounded by a plasma
membrane, which regulates what enters and
leaves the cell. Why is it important to regulate
what moves into and out of a cell?
FUNCTION
The cell membrane has a number of
functions:
1. Separates the cell from the surrounding
environment.
2. Controls what goes into and out of the cell.
The cell membrane is called selectively
permeable or semi-permeable.
3. Communicates with the environment inside
and outside of the cell.
I.
Bilayer of lipids with embedded proteins.
 Lipids are actually phospholipids

Phosphate layer “likes”
water because its polar.

Lipid tails
repel water.
Proteins are in various places along
membrane:
-Some are in outer surface
-Some are in inner surface
-Some are extended throughout
the membrane.
1. Transport proteins also Channel proteins.
-Assist materials in and out of cell.
2. Marker proteins- the cells “nametags”.
-They distinguish your cells from anyone
else’s cells.
3. Receptor proteins- receives messages for
the cell.



Very small molecules such as carbon dioxide,
oxygen and water. These materials move freely
through lipid bilayer because of their small size.
Small molecules made of lipids or molecules that
dissolve in lipids such as chloroform and alcohol
pass through easily. WHY?
ANS. Alcohol and chloroform will simply dissolve
through the cell membrane and into the cell because
the cell membrane is made up of lipids.


Ions such as sodium, potassium, and
calcium can pass through but only
through the protein channels.
Other small molecules such as glucose
and amino acids that the cell needs
will pass through but only through the
protein channels with help.
That’s all for today folks!
Now complete your Closing Thoughts!