OSMOSIS

A Type of Passive Transport

Definition Osmosis—The diffusion of WATER from

an area of high WATER concentration to an area of low WATER concentration

Most cells undergo osmosis because they are surrounded by watery solutionsThere are different amounts of

particles inside & outside of the cell• Sugars, amino acids, ions…

Movement of water

Water will move from where there is a lot of water (conc) to where there is a little water (conc)

The concentration of water will equalize on both sides but there will be more water molecules on one side

SALT SUCKS!!!! A simple rule to remember….

Salt is a solute, when it is concentrated inside or outside the cell, it will draw the water in its direction.

This is also why you get thirsty after eating something salty

Types of Solutions

When you put a plant or animal cell into a liquid containing water, one of three things will happen

1. Cell will swell2. Cell will stay the same size3. Cell will shrink

ISOTONIC A cell in an isotonic

solution has the same concentration in its cytoplasm as its surrounding environment Water will move

through the plasma membrane but it enters AND leaves at the same rate

"ISO" means the same

HYPOTONIC If the solution has “more

water conc. outside” than inside the cell the solution is hypotonic

More salt inside. Since salt sucks, water

will move into the cell. Water from high water

to low water conc.

The cell will gain water and grow larger. Swell

HYPTERTONIC If the solution has “more

water conc. inside” than outside the cell the solution is hypotonic

More salt outside Since salt sucks, water

will move out of the cell.

Water from high water to low water conc.

The cell will lose water and shrivel. SHRINK

Hyper kids go OUT to play

This is why it is dangerous to drink sea water - its a myth that drinking sea water will cause you to go insane, but people marooned at sea will speed up dehydration (and death) by drinking sea water.

This is also why "salting fields" was a common tactic during war, it would kill the crops in the field, thus causing food shortages.

PASSIVE TRANSPORT: FACILITATED DIFFUSION

Facilitated Diffusion—moves molecules that cannot readily diffuse through cell membrane even though there is a concentration gradientStill moving from high

to low Movement is assisted by

carrier proteins Does not require energy