CH. 3 ~ CELLS
Cell Membrane
1. Surrounds ALL cells
2. Has a “Phospholipid bilayer” which
makes it “flexible and “fluid”
Cell Membrane
“Phospholipid bilayer”
- Phosphate ‘head’ (polar- hydrophillic)
- 2 Lipid ‘tails’ (nonpolar- hydrophobic)
Cell Membrane
3. Semi-permeable – only allows certain
substances to pass through
4. Contains proteins- some used for
identification and some for transport (that
help to pass materials through).
Pics-Alpha/Beta Proteins- Text- p112
With a Hydrophobic Middle…
how does Water get through?
Aquaporins
Osmosis: Passive
movement of water
across a membrane
Two Ways:
Diffusion and bulk flow
(aquaporins)
• The membrane possesses integral proteins;
water transport integral proteins are called
aquaporins. Serves as a water-filled pipe
across the membrane.Dehydr..ADH/post pit…add aquaporins-Kidney/retain H O
2
Transport of materials
into and out of the cell
• Passive Transport – movement of molecules
that does not require energy.
– Usually from high concentration to lower
concentration
ex. Diffusion, Osmosis, Facilitated diffusion
• Active Transport – movement of molecules
that requires energy.
– Usually from low concentration to high
concentration (against the concentration gradient)
ex. Pumps, endocytosis, exocytosis
Review of Terms:
• Equilibrium – when 2 given areas have the
same concentration of molecules.
• Concentration Gradient – the difference in
concentration of molecules in 2 given areas.
• Defines HOW molecules will move, if going
WITH the concentration gradient (from high to
low = passive transport) or AGAINST it (from
low to high = requires energy = active transport
Passive Transport:
1. Diffusion –
movement of
molecules from
an area of high
concentration to
an area of lower
concentration.
Demos: Dye in Water
Sugar Cube
Passive Transport:
2. Osmosis – diffusion of water
Demo: Raisin in Water
3. Facilitated diffusion – passive transport of
materials across a cell membrane using protein
channels or carriers. (aka “Transport Proteins”
Increases the Rate of diffusion
Facilitated Diffusion
(TEXT: p 120- Example: Transport of Glucose)
Demo: Golf Ball: Bind, Change Shape, Release…Both In & Out
Protein Channels
Carrier Proteins
Facilitated Diffusion
Increases the rate of diffusion
• Similar to simple diffusion in the sense that
it is diffusion (across a membrane) from a
high concentration to a lower
concentration.
• However, this time the rate of diffusion is
greatly accelerated by the action of
membrane proteins that act as carrier
molecules and aid in diffusion.
http://www.northland.cc.mn.us/biology/Biology1111/animations/transport1.html
P/S-Notepage
Pictures of Passive and
Active Transport
Using a
Protein
Channel
Energy Added
Using a Protein
Pump
Active Transport: Pumps
• Type of active transport
• Move molecules from an area
of LOW concentration to an
area of HIGH concentration
• One example: the Na-K Pump
(Sodium-Potassium)
• Requires Energy
ACTIVE: Na-K Pump
(See diagram- back of notes….Ex: Basketball Pump)
*ONE Pump: does 450:300 Sodium OUT:Potassium IN every SECOND
Na+ binds,
ATP > ADP
K+
released,
ready for
Na+
Shape change
to original,
release of K+
ATP > ADP
Protein changes shape
Na+ (3)
released
from cell,
K+ binds
K+ binds (2),
releases another P
Active: Endocytosis and Exocytosis
http://www.northland.cc.mn.us/biology/Biology1111/animations/transport1.html
ACTIVE
Endocytosis
• Intake of material (food) using
the cell membrane
• Cell membrane surrounds
material and encloses it –
forming a vesicle/vacuole.
• Phagocytosis “cell eating” (WBC)
• Pinocytosis “cell drinking”
White Blood Cell
(WBC) engulfing
bacteria
Amoeba
Eating
ACTIVE
Exocytosis
• Removal of material (waste) from a cell.
• Golgi Apparatus “packages” the material
into a vesicle and sends it to the cell
membrane
• The vesicle fuses with the membrane
• The material is deposited outside the cell
Exocytosis
Electron Micrograph of
Exocytosis
•
This figure was taken from Alberts et al, Molecular Biology of the Cell,
Garland Publishing Third Edition, 1994
PASSIVE
ACTIVE
NO ENERGY
ENERGY
• Diffusion of
perfume, food
coloring
• Osmosis
• Facilitated diffusion
– Protein channels
– Carrier proteins
• Exocytosis
– GA packages and
secretes wastes
• Endocytosis
– Membrane
surrounds and
engulfs food, etc.
(Amoeba)
• Pumps
– Sodium-Potassium
There are 3 types of osmotic solutions
*Solute, Solvent, Solution Osmosis, Equilibrium/No Net Flow
• Isotonic - equilibrium
• Hypertonic – there is a greater
concentration of solute (ie, salt, the
‘stuff’) in the solution than in the cell
• Hypotonic – there is a greater
concentration of solute (ie, salt, the
‘stuff’) in the cell then in the fluid
around the cell
LESS ?
Solute
outside
MORE
Solute
outside
EQUAL
Solute
outside
Whenever solutes (dissolves substances) are
added to water, they decrease the number of
free water molecules; more solute molecules,
fewer free water molecules
Osmosis in
Red Blood Cells
Comparison of Plant and Animal
Cells in Osmotic Solutions
What is the major differences between what
happens in plant and animal cells when placed
in a hypotonic solution?
Diffusion and Osmosis Khan Academy 18.59
Onion Cell
PLASMOLYSIS
Secondary Cell Wall
From the adjoining cell- DO NOT
DRAW on diagram of ONE CELL
Primary Cell Wall
The ONE line to have in your drawing
Cell Mambrane
After Plasmolysis
DIALYSIS DEMO
• The small molecules of water and iodine
moved from an area of high concentration,
outside the cell, to an area of low
concentration inside the cell in order to try
to reach equilibrium. The large molecules
of starch were not able to diffuse and
reach equilibrium because they were too
large to pass through the semi-permeable
membrane.
Potential to move….
Pressure to keep out….
Hypoosmotic
Hyperosmotic
OP vs WP
Semi-Permeable
Water Molecule
Low OP,High WP
Hydration Shell
High OP,Low WP
Hydration Shells:
Water molecules
surrounding
solutes
A
-3
B
-7
Plants & water potential
• The combined effects of
1.) solute concentration
2.) physical pressure (cell wall)
can be measured as Water Potential 
• = psi
• is measured in megapascals (MPa)
• 1 Mpa = 10 atmospheres of pressure
Calculating Solute potential
• Need solute concentration
• Use the equation
 S = - iCRT
i = # particles molecule makes in water
C = Molar concentration
R = pressure constant 0.0831 liter bar
mole oK
T = temperature in degrees Kelvin
= 273 + oC (25)
Solve for water potential
(literal equation)
• Knowing solute potential, water potential
can be calculated by inserting values into
the water potential equation.

=
P
+
S
In an open container (or animal cell), P = 0
Diffusion and Osmosis Lab
• Bozeman 7.46
Water Potential Explained- powerpoint