Membrane and Osmosis - EG

Cell membrane

phospholipid bilayer separate external environment from internal environment

Phospholipid bilayer regulates…

what comes in and out of the cell

• chemical composition of cell membrane restricts what can move across it

Hydrophilic/polar molecules interact with…

OTHER polar molecules

Hydrophobic/nonpolar molecules interact with…

OTHER nonpolar molecules

Permeability

rate at which a specific type of molecule can move across the membrane

What do polar molecules need to cross the membrane?

pumps, transporters or channels

Passive transport

transport which does not require use of energy (ATP)

Simple diffusion

movement of solutes from an area of high concentration to low concentration across plasma membrane (ex. oxygen)

Facilitated diffusion

movement of solutes from high → low concentration via pumps, channels, transporters in the plasma membrane (ex. glucose, proteins)

Osmosis

movement of water (solvent) from high → low concentration across plasma memrbane (ex. water)

Active transport

movement of molecules from low → high concentration using transporters

• requires use of energy (ATP)

• water CANNOT use active transport

What is the direction of water or other solvent movement affected by?

• water/solvent concentration on each side of plasma membrane

• solute concentration on each side of plasma membrane (proteins, glucose, electrolytes)

Water molecules have net movement towards…

HIGHER osmotic conentration or total molar concentration of all solutes

Osmotic concentration/osmolarity

total concentration of all solutes in a solution

• measured in milliosmoles per liter (mOsm/L)

Hypotonic solution

solution w/ lower total solute concentration outside the cell and higher total solute concentration inside the cell

Hypertonic solution

higher total solute concentration outside the cell, and lower inside the cell

Isotonic solution

solution w/ same total solute concentration outside and inside the cell

• cell neither swells nor shrinks

• shape of cell not affected by net movement of water

Saturated fatty acids

fatty acids w/ no “kink” / bent

• phospholipids packed TIGHTLY in the membrane

Unsaturated fatty acids

fatty acids w/ “kink” / bent

• phospholipids packed LOOSELY in membrane

Temp affect on movement of molecules across plasma membrane

• increase = increase in movement of molecules

• decrease = decrease in movement of molecules

Concentration

the amount of a substance dissolved in a certain volume of solution

• direct in which molecules move depends on its concentration