Transcript Cell Membranes Osmosis and Diffusion

Cell Membranes
Osmosis and Diffusion
Functions of Membranes
1. Protect cell
2. Control incoming and outgoing substances
3. Maintain ion concentrations of various
substances
4. Selectively permeable - allows some
molecules in, others are kept out
Phospholipid Bilayer
Fluid Mosaic Model
Blood-Brain Barrier
• Allows some substances into the
brain, but screens out toxins and
bacteria
• Substances allowed to cross include:
water, CO2, Glucose, O2, Amino Acids,
Alcohol, and antihistamines. HIV and
bacterial meningitis can cross the
barrier.
Solutions
• Solutions are made of solute and a
solvent
• Solvent - the liquid into which the solute
is poured and dissolved. We will use
water as our solvent today.
• Solute - substance that is dissolved or put
into the solvent. Salt and sucrose are
solutes.
Methods of Transport Across
Membranes
1. Diffusion - Passive
2. Osmosis- Passive
3. Facilitated Diffusion- Passive
4. Active Transport- definitely NOT Passive
Methods of Transport Across
Membranes
1. Diffusion -passive transport - no energy
expended
2. Osmosis - Passive transport of water
across membrane
3. Facilitated Diffusion - Use of proteins to
carry polar molecules or ions across
4. Active Transport- requires energy to transport
molecules against a concentration
gradient – energy is in the form of
ATP
Diffusion
• Movement of molecules from an area of
high concentration to an area of low
concentration.
• Movement from one side of a membrane
to another, un-facilitated
Diffusion
Diffusion in Action
Osmosis
Tonicity is a relative term
• Hypotonic Solution - One solution has a
lower concentration of solute than
another.
• Hypertonic Solution - one solution has a
higher concentration of solute than
another.
• Isotonic Solution - both solutions have
same concentrations of solute.
Type of Solutions – Salts Suck
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
Diffusion and Osmosis are both types of PASSIVE
TRANSPORT - that is, no energy is required
The word "HYPO" means less,
• in this case there are less solute (salt)
molecules outside the cell, since salt
sucks, water will move into the cell.
• The cell will gain water and grow
larger. In plant cells, the central
vacuoles will fill and the plant
becomes stiff and rigid, the cell wall
keeps the plant from bursting
• In animal cells, the cell may be in
danger of bursting, organelles called
CONTRACTILE VACUOLES will
pump water out of the cell to prevent
this.
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.
• In plant cells, the central vacuole
loses water and the cells shrink,
causing wilting.
• In animal cells, the cells also shrink.
• In both cases, the cell may die.
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.
Plant and Animal Cells put into
various solutions
Types of Transport
Diffusion Lab
• We are using plastic baggies as the
cell membrane - It is selectively
permeable
• The solute is either the starch
solution or the iodine solution
• What is the solvent?
Membrane Permeability
•
•
•
•
Solute is eosin-starch-chloride solution
Solvent is Water
Indicator for presence of starch is IKI
Starch is made of amylose and amylopectin –
amylopectin is insoluble
• Iodine is not very soluble in water, but with KI
it forms a I3- (triiodine ion) which is soluble.
• I3- combines with the amylose and the starch
molecule turns blue-black.
Test for Starch
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