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7.3
Cell Boundaries
A. Cell Membrane
1. Cell membrane- regulates what enters and leaves the
cell and also provides protection and support.
2. ___________- double layered sheet that forms the core
of nearly all cell membranes
a. gives cell membranes a flexible structure that forms
a barrier between the cell and its surroundings.
3. __________ molecules- embedded in the lipid bilayer to
help move large molecules through the membrane, some
of which have carbohydrate molecules attached to them
4. _______________ act like chemical identification cards,
allowing cells to identify one another.
5. Fluid mosaic model- description of the cell membrane
because there are so many kinds of molecules embedded
in the membrane and it is constantly moving.
Draw and label a phospholipid.
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

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Label the fatty acids and the phosphate molecule.
Label which end is hydrophilic and hydrophobic.
Hydrophilic= _______________
Hydrophobic= _____________
↑ Label
-Cell membrane
-Carbohydrate chains
-Outside of cell
-Proteins
-Inside of cell
-Lipid bilayer
B. Cell Wall
1. Cell wall- provides_________________________.
a. are found in plants, algae, fungi, and many
prokaryotes.
2. The cell wall lies outside the cell membrane.
3. Most cell walls are porous enough to allow water,
oxygen, carbon dioxide, and certain other substances to
pass through easily.
C. Diffusion Through Cell Boundaries
1. Every living cell exists in a liquid environment.
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2. The cell membrane regulates movement of dissolved
molecules from the liquid on one side of the membrane
to the liquid on the other side.
D. Measuring Concentration
1. Solution- _____________________________________.
2. Solute- _______________________________________.
a. Ex: salt or sugar
3. Solvent- the substance doing the dissolving.
a. Ex: water
4. Concentration- of a solution is the mass of solute in a
given volume of solution, or mass/volume.
a. Ex: 12 grams of salt dissolved in 3 liters of water
b. Solute= salt
Solvent= water
c. Concentration= 12 g/3 L or 4 g/L
E. Diffusion
1. Diffusion- move from _______________ concentration.
No energy required.
2. Equilibrium- when the concentration of the solute is the
___________ throughout a system
Example:
 There is a higher concentration of solute on one side
of the membrane as compared to the other side of
the membrane.
 Solute particles move from the side of the membrane
with a higher concentration of solute to the side of
the membrane with a lower concentration of solute.
 The solute particles will continue to diffuse across
the membrane until equilibrium is reached.
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 When equilibrium is reached, solute particles
continue to diffuse across the membrane in both
directions.
 Draw an
arrow showing
the direction of
“solute particle
movement”
below the beaker
on the right.
In the beaker on
the right, draw
and changes in
water level or
number of solute particles on each side of the membrane that occur
as a result of the described process.
F. Osmosis
1. ______________- the diffusion of water through a
selectively permeable membrane.
2. Water diffuses from a highly concentrated region to a
less concentrated region.
3. ____________- the more concentrated solution (“above
strength”).
4. ___________- the more dilute solution (“below
strength”).
5. ___________- concentrations of solutions are the same
on both sides of a membrane (”same strength”)
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Draw an example of each type of solution; hypotonic,
hypertonic, and isotonic.
G. Osmotic Pressure
1. Osmosis exerts a pressure known as osmotic pressure on
the hypertonic side of a selectively permeable
membrane.
2. Because the cell is filled with salts, sugars, proteins, and
other molecules, it will almost always be hypertonic to
fresh water.
3. If so, the osmotic pressure should produce a net
movement of water into the cell. As a result, the volume
of the cell will increase until the cell becomes swollen or
bursts.
4. Cells in large organisms are not in danger of bursting
because they are bathed in fluids, such as blood, that are
isotonic.
5. Other cells are surrounded by tough cell walls that
prevent the cells from expanding even under tremendous
osmotic pressure.
H. Facilitated Diffusion
1. Cell membranes have protein channels that act as
carriers, making it easy for certain molecules to cross.
2. Facilitated diffusion______________________________________________
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______________________________________________
______________________________________________
3. Although facilitated diffusion is fast and specific, it is
still diffusion.
4. Facilitated diffusion will only occur if there is a higher
concentration of the particular molecules on one side of a
cell membrane as compared to the other side.
I. Active Transport
1. Active transport______________________________________________
__________________________________________.
2. Active transport requires energy.
Look at the diagrams.
Label each as either
facilitated diffusion or
active transport.
~ Which process can
move molecules from a
lower concentration
solution on one side of
the membrane to a
higher concentration
solution on the other
side.
A: active transport
~ Which process does not require energy?
A: facilitated diffusion
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J. Molecular Transport
1. Large molecules and even solid clumps of material may
undergo active transport by means of the cell membrane.
2. Endocytosis- the process of taking material into the cell
by means of infoldings, or pockets, of the cell
membrane.
3. The pocket breaks loose from the outer portion of the
cell membrane and forms a vacuole within the
cytoplasm.
4. Two examples of endocytosis are:
a. ____________- extensions of cytoplasm surround a
particle and package it within a food vacuole. The
cell then engulfs it.
i. requires a considerable amount of energy.
b. ____________- tiny pockets form along the cell
membrane, fill with liquid, and pinch off to form
vacuoles within the cell.
5. ____________- the membrane of the vacuole
surrounding the material fuses with the cell membrane,
forcing the contents out of the cell.
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