CELL MEMBRANES
and
TRANSPORT
AS Biology. Foundation. Cell
membranes and Transport
1
The Cell
AS Biology. Foundation. Cell
membranes and Transport
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Cell membrane
All living things are surrounded by a membrane.
A cell membrane is also known as plasma membrane.

Controls
exchange of materials such as nutrients and
waste between cells and their environment.
Has
other important functions for example to enable
cells to receive hormones.
To
understand the function of anything in biology, you
must study the structure first!
AS Biology. Foundation. Cell
membranes and Transport
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Cell Membranes from Opposing
Neurons (TEM x436,740).
Nerve cell
Cell membrane {
Gap between cells
}
cell membrane
7nm wide
Nerve cell
AS Biology. Foundation. Cell
membranes and Transport
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Cell membranes are made of
PHOSPHOLIPIDs




HYDROPHILIC heads
(water liking)
-Attracted to the
water
called POLAR
HYDROPHOBIC tails
(water fearing)
-Not attracted to the
water
called NON-POLAR
AS Biology. Foundation. Cell
membranes and Transport
A Phospholipid
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A phospholipid
HYDROPHILIC HEAD
At the other end of the phospholipid is a
phosphate group and several double
bonded oxygens. The atoms at this end
of the molecule are not shared equally.
This end of the molecule has a charge
and is attracted to water. It is POLAR
HYDROPHOBIC TAILS
The two long chains coming off of the
bottom of this molecule are made up of
carbon and hydrogen. Because both of
these elements share their electrons
evenly these chains have no charge. They
are NON POLAR. Molecules with no
charge are not attracted to water; as a
result water molecules tend to push
them out of the way as they are
attracted to each other. This causes
molecules with no charge not to dissolve
in water.
AS Biology. Foundation. Cell
membranes and Transport
3D model of a
Phospholipid
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A Phospholipid Bilayer
Phospholipids can form:
BILAYERS
-2 layers of
phospholipids with
hydrophobic tails
protected inside by the
hydrophilic heads.
The PHOSPHOLIPID
BILAYER is the basic
structure of membranes.
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membranes and Transport
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Fluid mosaic model
Cell membranes also contain proteins within the phospholipid bilayer.
This ‘model’ for the structure of the membrane is called the:
FLUID MOSAIC MODEL
FLUID- because individual phospholipids and proteins can move around
freely within the layer, like it’s a liquid.
MOSAIC- because of the pattern produced by the scattered protein
molecules when the membrane is viewed from above.
AS Biology. Foundation. Cell
membranes and Transport
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Cell Membranes from Opposing
Neurons (TEM x436,740).
} Phospholipid Bilayer
7nm wide
AS Biology. Foundation. Cell
membranes and Transport
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Movement of selected molecules
across the cell membrane
AS Biology. Foundation. Cell
membranes and Transport
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Methods of Transport
Across Membranes
1. Diffusion
2. Osmosis
3. Facilitated Diffusion
4. Active Transport
AS Biology. Foundation. Cell
membranes and Transport
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Methods of Transport
Across Membranes
Diffusion -passive transport - no
energy expended
2. Osmosis - Passive transport of water
across membrane
3. Facilitated Diffusion - Use of proteins to
carry polar molecules or ions across
4. Active Transport- requires energy to
transport molecules against a
concentration gradient – energy is
in the form of ATP
1.
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membranes and Transport
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Diffusion
 Movement
of molecules from an
area of high concentration to an
area of low concentration.
 Movement
from one side of a
membrane to another, unfacilitated
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membranes and Transport
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Diffusion
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membranes and Transport
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Solutions
 Solutions
are made of solute and a
solvent
 Solvent - the liquid into which the
solute is poured and dissolved. We
will use water as our solvent today.
 Solute - substance that is dissolved
or put into the solvent. Salt and
sucrose are solutes.
AS Biology. Foundation. Cell
membranes and Transport
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Osmosis
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membranes and Transport
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Tonicity is a relative term
 Hypotonic
Solution - One solution
has a lower concentration of solute
than another.
 Hypertonic Solution - one solution
has a higher concentration of solute
than another.
 Isotonic Solution - both solutions
have same concentrations of solute.
AS Biology. Foundation. Cell
membranes and Transport
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Plant and Animal Cells put into
various solutions
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membranes and Transport
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Types of Transport
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membranes and Transport
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Diffusion Lab
 We
are using dialysis tubing as
the cell membrane - It is
selectively permeable
 The solute is either the eosin
starch solution or the sugar
solution
 What is the solvent?
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membranes and Transport
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Membrane Permeability






Solute is eosin-starch-chloride solution
Solvent is Water
Indicator for presence of starch is IKI
Starch is made of amylose and
amylopectin – amylopectin is insoluble
Iodine is not very soluble in water, but
with KI it forms a I3- (triiodine ion)
which is soluble.
I3- combines with the amylose and the
starch molecule turns blue-black.
AS Biology. Foundation. Cell
membranes and Transport
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Test for Starch
AS Biology. Foundation. Cell
Elmhurst
College
membranes
andWebsite
Transport
22
Test for Chloride ions
 Indicator
for presence of chloride
ions is silver nitrate, AgNO3

A white precipitate, AgCl, forms if
chloride is present.
AS Biology. Foundation. Cell
membranes and Transport
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Test for Sulfate ions
 Indicator
for the presence of
sulfate ions is Barium chloride, BaCl


Barium sulfate, BaSO4 - forms a white
precipitate
BaCl + NaSO4 ----> BaSO4 + NaCl
AS Biology. Foundation. Cell
membranes and Transport
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Living Cells
 Fern
gametophytes are used to see
result of putting live cells in solutions
of varying tonicity
AS Biology. Foundation. Cell
membranes and Transport
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Osmosis
 We
will make an osmometer to see
osmosis
 Sugar solution in a dialysis tube is
used to simulate a cell membrane.
 Various concentrations of solute may
be used around the room.
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membranes and Transport
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 Moving
amoeba
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membranes and Transport
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