Water, water everywhere
and not a drop to drink…
-Samuel Taylor Coleridge
The Horse Latitudes
Why Are We Not Adivsed To
Drink Seawater?
Water Balance
• Need appx. 3L/day
• Without water, no hydrolysis, temperature
regulation, transport of materials
HYPONATREMIA
• 3 Gal/1hr = death due to loss of
electrolytes (salts), causing nervous
conductivity and muscle contraction to
cease
Which organelles maintain water balance?
Why must the cell membrane maintain
SELECTIVE PERMEABILITY?
Kinetic Molecular Theory
• Molecules are
constantly in motion
• Molecules want to
attain disordered
state / fewer collisions
• Molecules will move
until fewest number of
collisions/least
ordered state is
reached
BROWNIAN MOTION
• Molecules are
constantly moving as
a result of their own
vibrational/kinetic
energy
• This movement can
be observed as
BROWNIAN MOTION
PASSIVE TRANSPORT
• As molecules are constantly in motion,
they will move without requiring the
expenditure of energy by the cell
Diffusion v. Osmosis
DIFFUSION
DIFFUSION
• Passive movement of solute molecules
from high concentration to low
CONCENTRATION GRADIENT
• Molecules will tend to move from high
concentration to low concentration on their own
accord (using their own vibrational energy)
• Movement with the gradient is exergonic
OSMOSIS
• Passive movement of water molecules
from high to low concentration
OSMOTIC POTENTIAL
• DEF: The difference
between the
concentration of water
molecules inside and
outside of cell
• The larger the size of
this gradient, the
greater the potential for
water molecules to
move
DYNAMIC EQUILIBRIUM
• No net passive movement of solute or
solvent (water) due to an equal
concentration
• No concentration gradient or osmotic
potential
Factors Affecting
Diffusion/Osmosis
•
•
•
•
•
•
Tonicity of solution outside of cell
Selective Permeability of Membrane
Size of Particles
Weight of Particles
Charge of Particles
Temperature of Solvent
TONICITY
• Def: Relative measure of
dissolved particles
(solute) in the solution
surrounding the cell
membrane
• Measurement is always
compared to
interior/cytoplasm of cell
• Water does not have a
tonic classification as it is
invariably the solvent
ISOTONIC
• Concentration of
solute outside of the
cell is equal to the
concentration of
solute inside of the
cell
• No net movement of
particles
• DYNAMIC
EQUILIBRIUM
HYPOTONICITY
• Concentration of
particles outside of
cell is lower than
concentration inside
of cells
• If permeable, solute
will leave cell to
establish equilibrium
with outside
concentration
HYPERTONIC
• Concentration of
dissolved
particles/solute is
greater outside of cell
than in its interior
• As a result, solute will
attempt to enter the
cell to establish
equilibrium
CYTOLYSIS
PLASMOLYSIS
NORMAL
PLASMOLYSIS
• DEF: Loss of water
and turgor due to
placement of cell in
HYPERTONIC
environment
• Water leaves cell via
osmosis, causing
vacuole to shrink, or
cytoplasm to lose
volume (crenation)
CYTOLYSIS
• Def: Cells placed in
HYPOTONIC
environments may
undergo cytolysis/cell
rupture as water
enters the cell
• Loss of the lipid
bilayer ultimate
causes cell death
TURGOR
• In plants, the cell wall
resists cytolysis in
hypotonic
environments
• This turgor pressure
allows the plant to
resist gravity
Lab: Semipermeable Membranes
and Osmosis
• Purpose: To analyze the movement of
solutes and water across a selectively
permeable membrane
• Method: Tracking movement of solutes
and water achieved by use of organic
indicators and qualitative description of
turgor (rigidity of fluid filled container)
Dialysis
• Loss of kidney
membrane
permeability due to
disease or damage
requires dialysis
• Wastes are removed
from body by passing
blood through an
artificial cell
membrane
Protocol #1
• Fill beaker 2/3rds full with tap water
• Add Lugol’s solution until mixture is amber
• Test water with Tes-Tape to determine if glucose
is present in the bath
Protocol #2
• Open wet dialysis tube using fingers and glass rod. Tie
one end off with string
• Using seral pipettes fill tube with starch and glucose
solutions
• Tie off open end. Do NOT leave space for air
• Trim the strings and excess tubing
Protocol #3
• Immerse “cell” in iodine-water bath
• Allow to sit for 20 minutes while doing
Protocol #4
• After 20 minutes, qualitatively assess color
of bath, cell and turgidity of cell
• Retest water with Tes-Tape to check for
presence of Glucose
Protocol #4
• Observe Elodea cells in fresh water (premade slide) and sketch
• Make a 2nd slide using one Elodea leaf
and a drop of 6% NaCl solution
• Sketch the 2nd slide, noting any changes
between the fresh water and salt water
Did they or didn’t they…?
History of Cryogeny
Tonic Preserve: A Recipe
• At moment of death, sever head
• Place head in hypertonic glycerol bath
• Immerse glycerol-infused head into liquid
nitrogen bath.
• Keep until the year ????
• To thaw, remove head from liquid nitrogen
• Place head in hypotonic bath until dynamic
equilibrium is reached
• Enjoy