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Chapter 7 – Cell Transport
I. Cell (Plasma) Membrane
Recall from Chapter 7 that the cell membrane is
composed of lipids (because they can separate
substances.)
Cell Membrane (cont’d)
The membrane is made of many phospholipids
which have two parts: hydrophilic (water loving)
heads and hydrophobic (water fearing) tails.
Cell Membrane (cont’d)
Notice also that the membrane is made of two
layers of lipids called a lipid bilayer.
Cell Membrane (cont’d)
Also found in the cell membrane are
certain proteins, which play an important
part in the cell by:
1) Coordinating cell-to-cell behaviors.
2) Adjusting the cells metabolism rates.
3) Initiating growth & division times.
Summary of Cell Membrane
Structure
Membrane is semi permeable
Membrane is composed of a lipid bilayer
(2 layers of lipids and phosphates)
Membrane has many different types of
proteins embedded into it
These 2 things together make the fluid
mosaic model
Cell Membrane (cont’d)
A. Marker Proteins
Helps cells recognize
similar cells.
This is helpful for
when our defensive
cells encounter
bacteria with unknown
marker proteins, they
can then destroy them.
B. Receptor Proteins
 Helps cells receive materials/signals outside of the cell.
 When cells need stored energy from the pancreas, they
release signal molecules, which find and bind with the
pancreas cells to let them know to release some energy.
C. Channel/Carrier Proteins
Helps substances
move across the cell
membrane.
If substances are too
large to get through
the lipid bilayer
channel proteins
(doughnut shaped) act
as passage ways.
II. How Substances Move
 There are 2 types of transport across cell
membranes:
1. Passive – transport that does not need
any energy.
2. Active – transport that requires energy.
A. Passive Transport
Passive transport (no energy required)
can occur in 4 different ways:
i) Simple Diffusion
ii) Osmosis
iii) Diffusion through Ion Channels
iv) Facilitated Diffusion (Carrier Proteins)
Passive Transport (cont’d)
During passive transport substances
always move from high concentration
to low concentration (this is known as a
concentration gradient).
After passive transport when the
concentration of molecules is the same
we say equilibrium exists.
i) Diffusion
Diffusion is the movement of molecules
down a concentration gradient, from high
to low concentrations.
Examples: food coloring in water, perfume
spreading throughout a room, etc.
ii) Osmosis
Osmosis is the diffusion of water across a
semipermeable (cell) membrane.
It is the same process as diffusion except it
specifically means water movement.
a) Solutions
A solution is a mixture of solutes (things
being dissolved) and a solvent (things
doing the dissolving).
Water is typically the solvent. (i.e. sugar
cube in water, the sugar is the solute)
b) Types of Solutions
1. Hypertonic: solution with a higher concentration
of dissolved particles than its surroundings.
2. Hypotonic: solution with a lower concentration
of dissolved particles than its surroundings.
3. Isotonic: solution with an equal concentration of
dissolved particles to its surroundings.
c) Water Balance in a Cell
1. Cells placed in a hypertonic environment (salt
water) will plasmolysis. – SHRINK!
c) Water Balance in a Cell
2. Cells placed in a hypotonic environment (fresh
water) will cytolysis. – BURST!
c) Water Balance in a Cell
3. Cells placed in a isotonic environment will be
balanced.
Water Movement Problems
iii) Diffusion through Ion
Channels
An ion channel is a doughnut shaped
channel protein that is hydrophilic (polar)
inside.
Ions can pass through the channels
without contacting the hydrophobic
(nonpolar) part of the cell membrane.
Ion Channel (B)
iv) Facilitated Diffusion
Facilitated diffusion is a passive form of
transport caused by carrier proteins specific for
the molecules they transport.
Remember movement is always down the
concentration gradient. (i.e. high to low)
Also facilitated diffusion needs no energy.
a) Steps in Facilitated Diffusion
1. A molecule outside the cell binds to the
carrier protein.
2. The carrier protein transports the molecule
across the cell membrane.
3. The molecules are released inside the cell.

B) Active Transport
 There are many types of active transport,
but the 2 we will learn are:
i) The Sodium-Potassium (Na-K) Pump
ii) Movement by Vesicles
Active Transport (cont’d)
Active transport is the movement of
molecules up (against) the concentration
gradient, from low to high.
Remember this time the cell must use its
own energy (ATP) to move substances.
i) Sodium Potassium Pump
It takes 3 sodium ions out for every 2 potassium
ions put in the cell.
There is more sodium inside the cell and more
potassium outside the cell so the cell is working
against the concentration gradient.
Energy for the pump comes from ATP made by
the mitochondria.
ii) Movement by Vesicles
 There are 2 types of vesicles:
1. Endocytosis – into the cell.
2. Exocytosis – out of the cell.
Any Questions?
“Knowledge is not simply another
commodity. On the contrary. Knowledge is
never used up. It increases by diffusion
and grows by dispersion.”
--Daniel J. Boorstin