1. Movement Across a Membrane A Review
Grade 12 Biology

2. Definitions you need to know...
Diffusion
Concentration gradient
Passive transport
Equilibrium
Permeable
Impermeable
Selectively permeable
Channel protein
Carrier protein
Active transport
Sodium/Potassium pump

3. Questions you must be able to answer...
Why do molecules cross membranes?
What are cell membranes made of?
What molecules can get across a membrane by diffusion? Why?
What molecules can NOT cross a membrane without help? Why?
How do cells help molecules cross membranes?
Which processes require energy (ATP) and which will happen on their own?
What is the sodium / potassium pump and how does it work?

4. Diffusion is...
The movement of molecules from high concentration to low concentration
It is passive (requires no extra energy)
See diffusion happening

5. A concentration gradient is...
A difference in concentration across a membrane (high on one side, low on the other)
Passive transport is...
Movement of molecules that requires no energy
Equilibrium!
What will happen?
Equal concentrations on both sides

6. Now try the first question...
Why do molecules cross membranes?
HINT!

7. Selectively permeable means...
The membrane lets something cross it
Impermeable means...
The membrane does not let something cross it
Selectively permeable means...
The membrane lets some things through
but not others

8. Next question... What are cell membranes made of? Phospholipids
Polar
Polar
Non-Polar
Proteins

9. What molecules can get across a cell membrane by diffusion? Why?
Watch it happen!
What molecules can NOT cross a membrane without help? Why?
Polar
Non-Polar
Polar

10. A channel protein... A carrier protein...
Forms a tube through the non-polar part of the membrane
Helps large or polar molecules get through the cell membrane
A carrier protein...
Changes shape to let a
molecule cross the membrane
May require energy (ATP)
to change shape

11. How do cells help molecules cross membranes?

12. Active transport...
- is when ATP is needed to help molecules move across a membrane
- moves molecules against their concentration gradient (from low to high concentration)
Which one shows active transport?
Which one shows passive transport?
What is the difference between A and B?

13. Which processes require energy (ATP) and which will happen on their own?

14. The Sodium/Potassium pump...
Is a carrier protein
Puts sodium ions (Na+) out of cells against the concentration gradient
Puts potassium ions (K+) into cells against the concentration gradient
Needs ATP to work
See the pump work!

15. What is the sodium / potassium pump and how does it work?
Last review question...
What is the sodium / potassium pump and how does it work?
See the pump work!

16. Why is this important?
Example: your nervous system uses changes in concentrations across membranes to send messages