Cell (Plasma) Membrane
What is it made of?
Why is this a good material for a cell
membrane?
Cell Membrane
• Phospholipid bilayer
• Hydrophilic head
• Hydrophobic tail
Cell Membrane
• Homeostasis
– Steady state maintained by
the body
• Selectively Permeable
– Regulates what can come in
and out of the cell
Selectively Permeable (6.3)
CAN
Small Nonpolar
Breathing
– (O2)
– (CO2)
– WATER
CANNOT
– Large (glucose)
– Polar ( exception is water because its so
small)
– Ion (charged)
Proteins in the Cell Membrane
• “Fluid Mosaic Model”
– Many proteins will help
transport molecules
across the membrane
– Proteins drift freely
Membrane Proteins Embedded
1. Transport Proteins
2. Cell Recognition
Proteins- sugars hang off
proteins
3. Receptors Proteinsreceive signals
4. Enzymes- proteins that
make reactions happen
Cell Recognition Proteins
• Sugars hang off of proteins in the cell
membrane
• Give us different blood types
Receptor Protein
Receptor Proteinis a cell
membrane protein
that receives a
signal
Transport
Passive Transport: Diffusion
• Diffusion
• The movement of
particles HIGH
concentration to LOW
concentration
Why?
• Molecules are always in
random motion
Ex. Perfume, food
coloring, tea bag
Equilibrium- particles equally spread out
Osmosis Water ONLY!
- Diffusion of water from HIGH to LOW
concentration
Solute: Substance in solution that is dissolved
(ex. Sugar or Salt)
Solvent: Substance in solution that does the
dissolving ( ex. Water)
Hypotonic
Environment
TONICITY
Hypertonic
Environment
Isotonic
Environment
Isotonic
Diagram
97% H20
Where is the most water?
97%
H2H
O O
97%
2
Same
Which way does water go?
Inside and outside
Result?
Big words
Examples
Even, same concentration
overall
“dynamic equilibrium”
“homeostasis
contact lens
solution, Gatorade
Hypotonic
Diagram
92 % H20
Where is the most
water?
97% H2O
Outside
Which way does
water go?
Inside
Result?
Burst, get bigger; firm
Big words
Examples
“cytolysis”- to burst; “turgid”- get firm;
“turgor pressure” :pressure inside plant
cells to help stand upright
- Distilled water ( 100% Water)
- Plants standing upright
Hypertonic
Diagram
97% H20
Where is the most water?
Which way does water go?
Result?
Big words
Examples
80% Water
Inside
Outside
Smaller, shrink, go limp
“plasmolysis”- to wilt, shrivel, loss of
pressure; “flaccid”- go limp
Hypertonic
Red Blood Cells
Check Yourself
Is the lettuce in a hypertonic isotonic hypotonic
environment and why??
Poll
Passive Transport:
Facilitated Diffusion
Facilitated Diffusion
- diffusion across a
membrane through
transport proteins
Ex. sugars, ions ,
alcohol
NO ENERGY: From HIGH to LOW concentration
Active Transport
Movement of molecules across a membrane require
energy
• From LOW to HIGH concentrations!
Why?
• To maintain a certain internal environment:
• 1. Sodium Potassium Pump
Active Transport
Exocytosis &
Endocytosis
Exocytosis
- Removal of materials
- Vesicle fuses with
membrane, forcing
contents out
1.
Active Transport
2. Endocytosis
• process of taking in
materials by infolding of the
cell membrane
• Pocket breaks and forms a
vesicle in the cell
• Ex.
• Pinocytosis: take in
fluid
• Phagocytosis: Large
particle/food
• Amoeba
Concentration Gradient
measurement of how the concentration of
something changes from one place to another
B. Passive Transport:
molecules go DOWN concentration gradient from
HIGH to LOW concentration
C. Active Transport:
molecule go UP concentration gradient from
LOW to HIGH concentration
• Review Video of Transport
Elodea Plasmolysis
http://www.youtube.com/watch?v=2
Th0PuORsWY
“Egg”citing “Eggs”periment
Cell membrane
Egg Lab: Osmosis
Why does a plant like hypotonic but an
animal does not?
• http://www.phschool.com/science/biology_pl
ace/labbench/lab1/watpot.html