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)

MovementRapid Slow None

H20

O2

CO2

Sugars (glucose)

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)

3% salt (97% water)

H2OH2O

Hypertonic Solution = more salt outside of cell than inside• Water moves out of cell• Cell shrinks = plasmolysis

15% salt (85% water)

3% salt (97% water)

H2OH2O

Concentration Gradients

Isotonic Solution = concentration outside of cell equal to insideWater moves in an out of cell at same rate = no net

movement = equilibrium!

3% salt (97% water)

3% salt (97% water)

H2OH2O

Concentration Gradients

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 semi-permeable 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 Review1. 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 Transportb. Diffusionc. 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 ReviewIf 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 Review1. 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