Transcript Diffusion and osmosis - Sonoma Valley High School

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: Why do you think
this is called “passive”
transport?
concentration gradient
– Molecules are always moving.
– From area of high concentration to area of
low concentration.
– Equilibrium is reached when concentrations
are equal. (No concentration gradient)
Hint: Nature loves
balance. To remember
which way molecules
think of a rock rolling
down a hill – it does
not take as much
energy as pushing it
up a hill.
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 depends on:
– Size
– Lipid soluble.
– Appropriate pore
Hint: molecules that
pass the lipid bilayer
of the cell (plasma)
membrane are
hydrophobic, i.e.
nonpolar.
Everything else must
go through a protein
channel.
Passive Transport:Osmosis
• Osmosis
– Movement of
water molecules
through a
membrane from
high
concentration
area to low
concentration.
Think: what is the difference
between osmosis & diffusion?
Terms relating to osmosis.
• These terms always
describe the
surrounding solution
COMPARED to the
cell.
– Hypertonic: high
solutes - low water.
– Hypotonic: low solutes high water.
– Isotonic: equal solutes equal water.
Most cells do not explode
when filled with water, they
would from the excess water
first.
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 and squirt it out if
too much enters the cell.
How Plant Cells Deal With Osmosis
• Plant cells have turgor
pressure due to water
wanting to move into
the cell. (keep their
shape)
• Central water vacuole
fills.
• Pressure against the
cell wall is turgor
pressure.
Look: what happened to the
shape of the cell wall?
Filled water vacuole due to
hypotonic environment.
How Cells Deal With hypertonic solution
• Water leaves cell due
to hypertonic solution.
• Cytoplasm and
organelles move to
center of cell.
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.
• Animal cells in
hypertonic solution lose
water.
RBC’s cell in
Isotonic solution.
RBC’s cell in
hypotonic
solution.
RBC’s cell
in
hypertonic
solution.
Summarize the lecture in a paragraph
with a diagram that shows the
following:
• How water moves when a cell
has more water inside than out
and visa versa.
• What the following terms mean:
solute, solvent, solution.
• The diffusion of an drop of ink in
a glass of water over time.
• Explain this cartoon in terms of
how osmosis works.