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7.3 CELL TRANSPORT
CT Science Framework:
Explain the role of the cell membrane
in supporting cell functions.
A. Cell membrane
1.
Functions:
a. protective barrier
b. gives structure and shape
c. regulates what enters and exits a
cell
A. Cell membrane ( cont.)
2. Structure of
a. Double membrane
of lipids
-likes water ; repels
waters
b. Proteins are
embedded within the
layer
Photograph of cell membrane
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The cell membrane is a fluid mosaic of lipids, proteins, and
carbohydrates.
FLUID- because the molecules move about ; like a liquid
MOSIAC- because the proteins are scattered within the lipid
layer
B. Transport thru the cell
membrane
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1. Diffusion
a. passage of materials across a space
from an area of high concentration to
an area of low concentration until an
equilibrium is reached
b. Concentration: the mass of a solute
in a given volume of solvent
(grams/liter)
(example: 12 grams of salt in 3 liters of
water-what is the concentration?)
Diffusion (cont)
c. Equilibrium:
Concentration of a
substance is the
same across a space
Diffusion (cont)
Diffusion of a liquid
d. Factors that affect diffusion
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P E ST S
Permeability of the membrane
Electrical charge of the substanceneutrally charged substances move easier
Size of the molecule
Temperature speeds up diffusion
Solubility in water
A Cell’s Environment
is
AQUEOUS ( water-based)
Diffusion ( cont.)
2. Osmosis is a type of:
a. Diffusion of water across a space from
a point of high concentration to a point
of low concentration
b. Depends upon the concentration of a
solute in a given volume of solvent which
determines the type of cell solution
Osmosis ( cont.)
3. CELL SOLUTIONS:
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a. Isotonic Solution: the amount of
solute = the amount of solvent in and
out of the cell
Water moves in BOTH directions
Isotonic
Isotonic solution
Osmosis Cont.
b. Hypertonic Solution: Has a high
concentration of solute vs. solvent
 Cells SHRINK because they lose
water when placed in a hypertonic
solution
 Example of hypertonic solution is salt
water
Hypertonic
Hypertonic Solution
Osmosis ( cont.)
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c. Hypotonic solution: Has a LOW
concentration of solute vs. solvent
Cells SWELL when placed in a
hypotonic solution because they
GAIN water
Example: Fresh water
Hypotonic
Hypotonic Solution
Solution Environments:
Solution Environments:
HYPERTONIC
ISOTONIC
HYPOTONIC
4. In other words……
a. In an isotonic solution…..
-__________ happens to a cell, it looks the
___________
 b. In a hypertonic solution…….
-the cell _________ due to water ________
c. In a hypotonic solution………….
-the cell ________ due to water ________

4. In other words……
a. In an isotonic solution…..
-nothing happens to a cell, it looks the same
 b. In a hypertonic solution…….
-the cell shrinks due to water loss
c. In a hypotonic solution………….
-the cell swells due to water gain
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5. Facilitated Diffusion
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The use of membrane proteins to help
diffuse large particles ( eg-glucose, amino
acids) across a cell membrane.
Facilitated diffusion
C. Passive Transport
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1. Diffusion and osmosis are types of
passive transport.
a. Cell does not use energy to move a
substance across the membrane/space.
b. Cell energy is called ATP
D. Active Transport
1.
2.
3.
Energy (ATP) is required to move a
substance across the membrane/space.
Involves moving large materials into and
out of cell.
Types of
-Endocytosis: move materials into a cell
- Exocytosis: move materials out/exits of
cell
Endocytosis