Diffusion and osmosis
Describing Solutions
Sucrose Solution
– Solution: One or more substances distributed uniformly in
another substance.
– Solute: The substance dissolved in a solution.
– Solvent: The substance in which the solute is dissolved.
• Concentration: the measurement of the solute in a fixed
amount of solvent.
– Ex: 2% sugar solution = 2 grams sugar + 100 ml water.
Passive Transport
• Molecules
moving across
the plasma
membrane
without use of
cell’s energy.
Think: how does the membrane act as a barrier??
Concentration gradient
– Molecules are always moving.
– They move from areas of high concentration
to areas of low concentration.
– Equilibrium is reached when concentrations
are equal. (No concentration gradient)
Diffusion
• The movement of any molecule in solution from high
concentration to low concentration
– Membranes allow some molecules to pass others not to pass.
• Ability to pass through the membrane depends on:
– Size
– Lipid soluble.
– Appropriate pore
Think: what happens when
you put a drop of dye in water?
Passive Transport:Osmosis
• Osmosis
– Movement of
water molecules
through a
membrane from
high
concentration
area to low
concentration.
Terms relating to osmosis.
– Hypertonic; high
solutes - low water.
– Hypotonic; low
solutes - high
water.
– Isotonic; equal
solutes - equal
water.
Which way is the WATER moving in each of the pictures?
How Cells Deal With Osmosis
• Freshwater single cell
organisms:
• Water moves in due to
osmosis.
• Excess water collected
by contractile vacuole.
• Water is expelled from
organism.
Contractile vacuole collecting water
in a paramecium.
How Plant Cells Deal With Osmosis
• Plant cells have turgor
pressure due to water
wanting to move into
the cell.
• Central water vacuole
fills.
• Pressure against the
cell wall is turgor
pressure.
Filled water vacuole due to
hypotonic environment.
Think: why do plants “droop” when they
need water?
How Cells Deal With hypertonic solution
• Plasmolysis is loss of
turgor pressure.
• Water leaves cell due
to hypertonic solution.
• Cytoplasm and
organelles move to
center of cell.
• The cell wall helps the
cell keep its shape.
Elodea cell in hypertonic solution.
How Animal Cells Deal With Osmosis
• Animal cells must be in
isotonic solution.
• Animal cells in a
hypotonic solution gain
water.
– Cytolysis results( they
burst apart)
• Animal cells in
hypertonic solution lose
water ( they shrivel up
and die)
Relate the Latin roots
“iso”, ‘hypo’ and ‘hyper’ to
these solutions
RBCs in Isotonic
solution.
(RBC= red blood cell)
RBCs in
hypotonic
solution.
RBCs in
hypertonic
solution.
Summary paragraph
• 1. What is the difference between a solute
and a solvent?
• 2. How is osmosis a type of diffusion?
• 3. Meat can be kept without refrigeration
by salting it. What would happen to a
bacteria if it was in a super salty solution?