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Cell Membrane: Structure and
Function
Interest Grabber
In or Out?
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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 cell membrane,
which regulates what enters and leaves the cell.
Why is it important to regulate what moves into
and out of a cell?
Figure 7-12 The Structure of the
Cell Membrane
Section 7-3
Outside
of cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside
of cell
(cytoplasm)
Protein
channel
Lipid bilayer
Cell Membrane
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Function = controls what enters the
cell and what leaves the cell
Made of a lipid bilayer
Has proteins
Has some carbohydrates, which
help with identification
Is fluid (fluid mosaic model)
Diffusion
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Def. of diffusion = Spreading of
molecules in a given space.
What happens?
-Substances move from an area
where there is more of them to an
area where there is less of them
Diffusion
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Def. of permeable = membrane that
lets substances pass through it
Cell membrane is selectively
permeable, which means that it lets
some things in but does not let other
things in
Substances keep moving till there is
about equal amounts of them on
both sides of the membrane
Facilitated Diffusion
Section 7-3
Glucose
molecules
High
Concentration
Cell
Membrane
Low
Concentration
Protein
channel
Factors that Affect Diffusion
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Amounts of substances involved
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Temperature
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Pressure
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Stirring
-speeds up the rate of diffusion
Osmosis
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Def. of osmosis = movement of
water from greater to lesser
Figure 8.11 Osmosis
Figure 8.12 The water balance of living cells
Osmosis
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Some one-celled organisms have a
contractile vacuole that pumps
water out of a cell (Paramecium)
In plants, as water goes into the
cell, it builds up pressure that
pushes against cell wall. This is
called turgor pressure.
Contractile Vacuole
Passive Transport
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NO ENERGY NEEDED!
Is the movement of small molecules in
and out of a cell
Molecules go from greater to lesser
(WITH- concentration gradient)
Examples: amino acids, fatty acids,
glycerol, simple sugars (glucose)
Passive Transport
Active Transport
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ENERGY NEEDED!-word ‘pump’ is used to get
charged or big molecules across membrane
Molecules go from lesser to greater (AGAINST
concentration gradient)
This is when large molecules are pulled through
the cell membrane by the use of ENERGY
Do not fully know how it works
Figure 7-19 Active Transport
Section 7-3
Molecule to
be carried
Energy
Molecule
being carried
Endocytosis and Exocytosis
(ACTIVE TRANSPORT)
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Def. of endocytosis = process by
which cells take in large molecules
large volumes from the outside
-ex. Pinocytosis (liquid) and
phagocytosis (solids)
Def. of exocytosis = process by
which cells get rid of large
molecules in the cell
Phagocytosis: Engulfing
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This is when large molecules are
surrounded and pulled into the cell
Examples: amoeba, white blood
cells called phagocytes
This is the same method used by
white blood cells to trap bacteria in
our blood
Phagocytosis: Engulfing