1. Cell Transport (7.3)

2. Passive Transport
Important: Keep the cell’s internal conditions relatively constant
Cell needs to be regulate the movement of molecules from one side of the membrane to the other
Diffusion
the process in which particles move from an area of higher concentration to an area of lower concentration
this is the force behind moving particles into and out of the membrane
The particles moving from an area of high concentration to an area of lower concentration will occur until the particles reach equilibrium (particles are the same concentration on both sides)
After equilibrium: the particles will continue to move back and forth, but will remain of equal concentrations
depends on RANDOM MOVEMENT of particles → substances diffuse across the membrane without using additional energy (PASSIVE TRANSPORT)

4. Passive Transport
Most molecules that diffuse through the lipid bilayer easily are small and uncharged
Large and charged molecules have the ability to pass through the membrane as well → facilitated diffusion
Facilitated Diffusion
the process where molecules CANNOT directly diffuse across the membrane but pass through special protein channels
hundreds of proteins have been discovered that help in facilitated diffusion
Since it is still diffusion, it does not require the cell to use energy to pass the molecules through the membrane
Ex: Red blood cells have special proteins that allow glucose into the cell

6. Osmosis
Water needs special channel proteins to move water into and out of the cell → aquaporins
Osmosis: the diffusion of water through a selectively permeable membrane
molecules still move from an area of higher concentration to an area of lower concentration
the semipermeable membrane allows for the water particles to move from one side to the other, but NOT the solute particles (pg 210)
Equilibrium: the water and sugar will be equal on both sides of the membrane

7. Osmosis (pg 211)
1. Isotonic (same strength): the concentration of solutes are the same inside and outside the cell. The water moves back and forth equally.
2. Hypertonic (above strength): the solution has a higher solute concentration than the cell. The movement of water out of the cell causes it to shrink.
3. Hypotonic (below strength): The solution has a lower solute concentration than the cell. The water movement is into the cell causing it to swell.

9. Osmotic Pressure
Osmotic pressure: the movement of water into or out of the cell
Cells are almost always hypertonic in fresh water because they contain salts, sugars, and other dissolved proteins → this causes water to move into the cell causing it to swell and burst
Cells are mostly surrounded by isotonic solutions (blood) so this is not a reoccurring problem
Plant cells
Hypertonic and Hypotonic solutions do not interfere with a plant cell’s structure, but they can cause injuries to the cell wall

10. Active Transport
Active transport: the movement of material against a concentration gradient
Requires energy
Usually small molecules or ions are carried through the membrane using protein pumps that are found in the membrane itself
Ions (charged molecule): calcium, potassium, and sodium
larger molecules are actively transported through endocytosis or exocytosis → this usually involves changes in shape of the cell membrane
considerable amounts of energy are needed for active transport (ATP)

11. Active Transport (pg 212)
Endocytosis: the process of taking material into the cell by means of infoldings (pockets) of the cell membrane → the pocket breaks off and becomes a vesicle in the cytoplasm
Phagocytosis (phago = to eat): extensions of cytoplasm surrounding a particle and package it within a food vacuole
Requires a considerable amount of ENERGY
Ex: White blood cells eat damaged cells
Pinocytosis (pino = to drink) : cells take up liquids from the surrounding environments and pinch off to form vacuoles within the cell
Exocytosis: the release of large amounts of material from the cell
the membrane of the vacuole fuses with the cell membrane and forces the contents out
Ex: Removal of water using a contractile vacuole