Membrane Transport (Passive Transport)

Passive transport

no energy required (move down [ ] gradient)

active transport

energy ATP required (move against [ ] gradient)

3 types of passive transport

1. Simple diffusion

2. facilitated diffusion

3. osmosis

concentration gradient

natural movement of molecules from high concentration to areas of low concentration

3 factors of the speed of diffusion

concentration, molecular size, and temperature

Simple diffusion

small nonpolar substances diffuse through the membrane (hydrophobic substances)

Simple diffusion examples

water, oxygen, carbon dioxide, steroid hormones, fatty acids

facilitated diffusion

Channel or carrier required for certain hydrophobic, nonpolar, or large molecules.

Carrier-mediated facilitated diffusion

Substances bind to protein carriers

Channel-mediated facilitated diffusion

Substances move through water-filled channels

Carriers

transmembrane integral proteins (saturated)

aquaporins (AQPs)

Water channels

2 types of Channel-mediated facilitated diffusion

Leakage channels (always open) and Gated channels (Controlled by chemical or electrical signals making them open or closed)

Osmosis

movement of solvent (water)

Osmolarity

measures concentration of solute particles in a solvent

Hydrostatic pressure

Osmosis increases cell volume, exerting outward pressure on the membrane.

Osmotic pressure

inward pressure due to tendency of water to be “pulled” into a cell with higher osmolarities

Tonicity

Ability of a solution to change the shape or tone of cells by altering the cells’ internal water volume

3 types of Tonicity

Isotonic solution, Hypertonic solution, Hypotonic solution

Isotonic solution

has same osmolarity as inside the cell, so volume remains unchanged

Hypertonic solution

has higher osmolarity than inside cell, so water flows out of cell, resulting in cell shrinking (crenation)

crenation

shrinking of the cell

Hypotonic solution

has lower osmolarity than the inside of the cell, so water flows into cell, resulting in cell swelling (lysing)

lysing

cell bursting