Water and its relation
to
Osmosis & Diffusion
Living cells contain aqueous
(water) solution and they are
surrounded by aqueous solutions
 If
the concentration of dissolved
substances (solutes) is not the same
inside and outside the cell –

A process called osmosis occurs
 Osmosis:
the movement of water molecules from an
area with less solutes (low concentration) to
an area with more solutes in the solution
(high concentration)

The water passes through the semi-permeable
membrane until the concentration of the
solutes is the same on both sides.
 Osmosis
is the
movement of water
(red dots) through
a semi permeable
membrane to a
higher
concentration of
solutes (blue dots).
What are semi-permeable
membranes?

Those membranes that allow the solvent (liquid),
but not the solutes to pass from one side of the
membrane to another

EX: egg, cellophane, and cell membranes

In these membranes the pores are large enough
for water to pass through but too small for other
compounds to pass
Examples
 Sailor
died from dehydration due to the
high concentration of salt in the seawater.
 After drinking the seawater the high
concentration of salt caused the water to
travel out of his cells.
 This caused the cells to dehydrate or
shrink
How do we
get pickles?
cells contain aqueous solutions –
intracellular fluid
 The cells are also surrounded by an
aqueous solutionintercellular fluid
 Cells function and survive by keeping
the concentration within and around the
cell approximately the same.
 Living

If the concentration of solute in the fluid
surrounding the cell is higher than inside the
cell the solution is hypertonic
 Water will travel out of the cell through the
membrane - crenation
Red Blood Cells in a Hypertonic
Solution
Hypertonic Solution

The word "HYPER"
means more, in this case
there are more solute
(salt) molecules outside
the cell, which causes
the water to be sucked in
that direction.
 If
the concentration of the solute outside the
cell is less than inside the cell it is called a
hypotonic solution.
 Hemolysis will occur – additional water will
travel into the cell causing it to swell and
rupture.
Red Blood Cells in a Hypotonic
Solution
Hypotonic Solution

The word "HYPO"
means less, in this
case there are less
solute (salt)
molecules outside the
cell, so water will
move into the cell.

When the fluids have the same concentrations
they are called isotonic
 EX: when fluids are administered to a patient
Red Blood Cells in an Isotonic
Solution
Isotonic Solution

If the concentration of
solute (salt) is equal
on both sides, the
water will move back
in forth but it won't
have any result on the
overall amount of
water on either side.
 "ISO" means the
same
What is Diffusion?
 Diffusion
is the natural tendency of
molecules to flow from higher
concentrations to lower concentrations
 The rate of diffusion depends on the
weight of the molecules—heavy molecules
diffuse more slowly than light molecules.
Diffusion of Gases
A
bottle of perfume opened in one
corner of a room would slowly fill the
room
 Molecules
disperse from a concentrated
source, the newly opened bottle, until
they are evenly distributed throughout
the room
 Smell
of freshly baked cookies
Diffusion of Liquids
 When
two fluids mix together without any
help from us.
 We can explain this using the idea that
particles move.
 Instead of the particles moving around
and mingling with particles of the same
material, they move around and mingle
with particles of the other material as well
How Diffusion of Liquid in
Liquid Works
 Add
a drop of food coloring in a container
of water.
 The
color will “diffuse” or disperse
throughout the entire sample until the
sample is a uniform color.
http://paer.rutgers.edu/pt3/movies/mixing2.mov
How Diffusion of Solid in
Liquid Works
 The
solute (solid) dissolving in the solvent
is also an example of diffusion.
 The water “attacks” the solute which
eventually dissolve.
 What are ways that this process in
increased?
How Diffusion of Solid in
Liquids Works
Diffusion across a Membrane
Selectively Permeable membranes –
Living membranes alter what may pass
through at any given time
Diffusion of CO2 and O2 in the Lung
Kidney Dialysis
Review
 Osmosis:
the movement of water
molecules from an area of low solute
concentration to an area of high solute
concentration.
 The
water passes through the semipermeable membrane until the
concentration of the solutes is the same
on both sides.
 Diffusion
is the natural tendency of
molecules to flow from higher
concentrations to lower concentrations
 Movement
may be of molecules or ions
across a semi-permeable membrane
 Depends
on molecular size, ionic charge,
and molecular solubility (ability of solute
to dissolve in solvent)
Diffusion or Osmosis?
1% salt (low concentration) in
the bag
10% salt (high concentration)
surrounding the bag
Which way does the water
move?
Diffusion or Osmosis?
Iodine solution in the bag
Starch solution surrounding
the bag.
What do you predict will
happen?
Lab Set-up