Chapter 7, section 3:
Cell Transport
Movement of Materials Across Membranes
Remember Homeostasis?
In order to live, cells must obtain certain
materials from their environment. They must
also get rid of waste products. The cell
membrane allows this.
Cell Membrane
– Lipid bilayer (two layers of phospholipids)
– Proteins embedded in and on a “sea” of
lipids = fluid mosaic (like boats floating
around) [video]
Cell Membrane
Selective Permeability = only certain materials may
move through the membrane
(permeability = ability to pass through)
Rapid
H20
O2
CO2
Movement
Slow
Sugars
(glucose)
None
Large Molecules
(e.g. starch)
Transport Across Membranes
Active Transport = cell must use energy to
move molecules across membrane
•
Use ATP (Adenosine TriPhosphate) for energy
Transport Across Membranes
Passive Transport = movement of a substance
without the need for the cell to use energy
•
Diffusion = movement of molecules from an area of
high concentration to an area of low concentration
Transport Across Membranes
Osmosis = diffusion of water across a membrane.
Always moves from an area of high
concentration (of water) to an area of low
concentration.
Let’s see osmosis in action!
Concentration Gradients
Hypotonic Solution = less salt outside of cell than inside
• Water moves into cell
• Cell expands! Animal cells explode; plant cell walls
prevent this.
1% salt (99% water)
H2O
H2O
3% salt (97% water)
Concentration Gradients
Hypertonic Solution = more salt outside of cell than inside
• Water moves out of cell
• Cell shrinks = plasmolysis
15% salt (85% water)
H2O
H2O
3% salt (97% water)
Concentration Gradients
Isotonic Solution = concentration outside of cell equal to inside
Water moves in an out of cell at same rate = no net
movement = equilibrium!
3% salt (97% water)
H2O
H2O
3% salt (97% water)
Kidney Function
Demo Analyses
• Starch in a bag: answer questions 1-3 on
page 187.
• Egg demo:
1. What does the egg represent?
2. What happened to the egg in tap water?
Corn syrup?
3. What process occurred that caused the
results that you observed? Explain.
Review questions
Putting salt on a slug causes it to shrivel up
and die. Explain this using osmosis.
Why does putting salt on a slug kill it?
This is due to osmosis. The skin of the slug acts as a semipermeable membrane where there are different concentrations of
salt and water on each side. Remember that water will move from
an area where there is more water to an area where there is less
water. The salt that you sprinkle on the slug mixes with water in the
slime on the outside of the slug to make a salty solution. In any
solution there is only so much room, so if there is a lot of salt, there
is not a lot of water. There is more water, less salt on the inside of
the slug, so water leaves the slug to mix with the salt outside the
slug in order to equalize (or "more equalize") the water on both sides
of the membrane. There is a net loss of water from the slug and it
dehydrates to death.
More Review
1. A skunk sprays stinkiness into the air. The
odor moves from an area of high concentration
to an area of low concentration. This is an
example of _________.
a. Active Transport
b. Diffusion
c. Osmosis
2. True or false? If a cell (3% salt) is placed in a
hypertonic solution, then the salt will go into
the cell and absorb the water, causing the cell
to shrink.
More Review
If a cell (3% salt) is placed into a solution…
1. …containing 10% salt, then __________.
2. …containing NO salt, then ___________.
3. …containing 3% salt, then ___________.
A. Water will move into the cell
B. Water will move out of the cell
C. There will be no net movement of water
More Review
1.
Protein and phospholipid molecules float around. This
is why the plasma membrane is called a __________.
a. Bilayer
b. Fluid mosaic
c. Selective Permeability
2. If a cell must use energy to transport a molecule, then
the process is _________.
a. Active Transport
b. Diffusion
c. Passive Transport