1. Movement Across the Cell Membrane
Cell Biology standard 1a
Students know cells are enclosed within semipermeable membranes that regulate their interaction with their surroundings.

2. A. Cell Membrane Cell Membranes surround ALL cells!
Controls what molecules enter and leave the cell
- food & oxygen molecules must enter the cell
- waste products need to be released
SEMIPERMEABLE – it allows some things through but not others

4. Structure of Cell Membrane
Phospholipid bilayer
Polar heads “love” water (hydrophilic)
Nonpolar tails “fear” water (hydrophobic)

5. C. Fluid Mosaic Model
Describes the various molecules found in the cell membrane
Example:
-Proteins: forms channels and pumps to move materials across membranes
- Carbohydrates: act like identification cards so cells can identify one another

7. D. Transport Across a Membrane
Molecules can enter/leave the cell in 2 ways:
1. Passive Transport
* Diffusion
* Carrier-Facilitated (“helped”) Diffusion
* Osmosis
2. Active transport
* Protein Pump
* Endocytosis
* Exocytosis

8. Passive Transport
Energy is not required for movement across the membrane to occur
Molecules move from area of high concentration to area of low concentration
Example: Like riding a bike downhill

9. Two factors determine if passive transport takes place, equilibrium and permeability
- Equilibrium: when the concentrations on both sides of the membrane are equal
membrane

10. - Permeability: ability of a molecule to diffuse (move) across a membrane
* Impermeable: molecules that cannot pass across a membrane
* semi-permeable/selective permeability: Some molecules can pass across the membrane while other molecules cannot

11. A. Diffusion
Molecules moving from area of high concentration to area of low concentration
No energy is required
Occurs because molecules constantly move and collide with each other
higher conc lower conc.
Cell membrane

12. B. Carrier-Facilitated Diffusion
No energy required
Molecules “helped” across by carrier proteins from high to low concentration

14. C. Osmosis Osmosis is a special type of diffusion
The diffusion of water molecules through a selectively permeable membrane

15. HYPOTONIC
Solution has a lower solute concentration than the inside of cell
More water enters cell, causing cell to expand (get big)
ISOTONIC
Concentration of solutes (dissolved substance) is the same in and out of the cell
Equal amount of water leaving and entering cell
HYPERTONIC
Solution has a higher solute concentration than the inside of cell
More water leaves cell, causing cell to shrink

16. Active TransPort Energy required for molecules to pass across
ATP – the “battery” of the cell
Breaking a bond in ATP releases energy
Can “pump” molecules from low to high concentration (against concentration gradient)
Example: Like riding a bike uphill
ATP

17. A. Protein Pump Protein Pumps: pulls molecule through
ATP Energy is required

18. B. Endocytosis
Endocytosis: cell membrane engulfs the larger molecule bring it into the cell
Two types:
Phagocytosis: cytoplasm surrounds a molecule and packages it in a food vacuole
Pinocytosis: cell membrane forms pockets filled with liquid and pinch off to form vacuoles in a cell

21. C. Exocytosis
Exocytosis: The membrane of the vacuole surrounding the material fuses with the cell membrane, releasing the material outside the cell