Section 6.3 How Substances Move across Bilayers

concentration gradient

created by a difference in solute concentrations

net movement

from high-concentration regions to low-concentration regions

Diffusion along a concentration gradient

Diffusion along a concentration gradient

Equilibrium occurs

when the molecules or ions are randomly distributed

Molecules are still moving randomly but there is

no more net change

Passive transport

substances diffuse in the absence of an outside energy source

Diffusion across a Selectively Permeable Membrane

all happens spontaneously

Osmosis

diffusion of water moves quickly across lipid bilayers

Osmosis only occurs across

selectively permeable membranes

Water moves from regions of ? solute concentration to regions of ? solute concentration

low to high

•Osmosis dilutes the ? concentration of solute

higher

•Equalizes concentration on ? sides of the bilayer

both

Osmosis is ? and moves from ? to ?

It is counter: moves from low to high;

Hypertonic solution

Solute concentration is HIGHER outside vs. inside

Water will move out of the cell by osmosis

what happens to a cell in Hypertonic solution

CELL WILL SHRINK

Hypotonic solution

•Solute concentration is LOWER outside vs. inside

•Water will move into the cell by osmosis

what happens to a cell in a Hypotonic solution

CELL WILL EXPAND

Isotonic solution

•Solute concentration is = outside vs. inside

•No net water movement

what will happen to a cell in Isotonic solution

The cell size will remain the same