1. Cell Transport

2. Types of Transport
Passive Transport: does not require energy to move substances across the cell membrane
Active Transport: requires energy to move substances across the cell membrane

3. Passive Transport Vocabulary
Equilibrium: when there is an equal number of molecules on both sides of the cell membrane
Concentration: the amount of a particular substance in a given volume
Concentration Gradient: When there is a higher concentration of a substance on one side than the other
Diffusion: When a substance moves from an area of higher concentration to an area of lower concentration

4. Passive Transport
When substances enter or leave the cell by diffusing across the cell membrane down their concentration gradient
The direction the substances move depends on the concentration gradient

5. Types of Passive Transport
Simple Diffusion
Facilitated Diffusion
Osmosis

6. Simple Diffusion
When small, nonpolar (uncharged) substances pass directly through the lipid bilayer from an area of higher concentration to an area of lower concentration
Ex: If there is more oxygen outside the cell than inside the cell, it will diffuse across the lipid bilayer and into the cell.

8. Facilitated Diffusion
Substances that cannot pass directly through the membrane are helped to diffuse through the membrane using transport proteins

9. Transport Proteins
Channel Proteins: Serve as a tunnel through the lipid bilayer that allow ions, sugars, and amino acids to pass through the membrane
Each channel only allows specific substances to pass through
Ex: The channel for sodium ions does not allow sugars to pass through

10. Transport Proteins
Carrier Proteins: Only transport substances that fit within their binding site through the cell membrane
Carrier protein binds to a specific substance on one side of the cell membrane, changes shape and allows the substance out on the other side of the cell membrane

11. Osmosis
Facilitated diffusion of water from an area of higher concentration to an area of lower concentration
Allows the cell to maintain water balance as their environment changes

12. Water Channels
Since water is a polar substance, it does not directly diffuse across the cell membrane
So the cell has specific protein channels that only allow water to pass through

13. Predicting Water Movement
The direction the water moves depends on the concentration of the cell’s environment

14. Hypertonic Water moves out of the cell
There is more solute outside the cell than inside the cell
The cell loses water and shrinks

15. Hypotonic Water moves in
There is more solute inside the cell than outside the cell
Cell gains water and expands

16. Isotonic
There is the same concentration of water inside the cell and outside the cell
Equilibrium is reached
Cell stays the same size

17. Active Transport
Transport of substances against their concentration gradients
Requires energy usually in the form of ATP

18. Use of Carrier Proteins as Pumps
Carrier proteins require energy to pump substances across their concentration gradient

19. Sodium-Potassium Pump
Sodium ions inside the cell bind to the carrier protein which changes shape and releases sodium ions outside the cell membrane
As a result a phosphate group is released from the pump, returning the channel protein to its original shape, and releasing potassium ions inside the cell
For every three sodium ions pumped out, two potassium ions are brought inside
This prevents sodium from building up inside the cell, which would cause the cell to burst due to osmosis bringing in too much water

20. Vesicles
Large substances are too big to cross the membrane in channel proteins so they use vesicles
Vesicle membranes are lipid bilayer, so they can bud off from the cell membrane or fuse with it to move large substances in or out of the cell

21. Endocytosis
The movement of large substances into a cell using a vesicle
The cell membrane forms a pouch around the substance that closes and then pinches off inside the cell
Pinocytosis: also known as cellular drinking, engulfing liquid particles
Phagocytosis: engulfing solid particles

22. Exocytosis
The movement of large substances out of a cell using a vesicle
Vesicles inside the cell fuse with the cell membrane and are released outside the cell
Used to transport proteins modified by the Golgi apparatus, excrete wastes, or remove bacteria