Lab #3: Diffusion, Osmosis &
the Functional Significance of
Biological Membranes
Biology for Today (BIO-1505)
DEFINITIONS TO KNOW:
• Tonicity: Comparing one solution concentration to that
of another.
• Hypotonic: Low solute – High solvent
• Hypertonic: High solute – Low solvent
• Isotonic: Equal solutes
• Solute: a dissolved substance
» (e.g. salt-NaCl)
• Solvent: a substance capable of dissolving another
» (e.g. water).
More…
DEFINITIONS TO KNOW:
• Tugor Pressure: force against a cell wall after
an influx of water due to osmosis.
• Plasmolysis: shrinkage of cytoplasm and the
pulling away of the plasma membrane from the
cell wall when a plant cell loses water.
• Hemolysis: rupturing of a red blood cell
followed by the release of hemoglobin.
• Crenation: the margin of scalloped projections
in a shriveled cell.
Hypotonic vs. Hypertonic
“SOLUTION A”
HYPOTONIC
Low solute
concentration
“SOLUTION B”
HYPERTONIC
High solute
concentration
•Solution A is hypotonic with respect to Solution B.
•Solution B is hypertonic with respect to Solution A.
DIFFUSION
• Defined: The movement of solute
molecules across a selectively permeable
membrane, from a region of high
concentration to a region of lower
concentration. (“down the conc. gradient”)
• Diffusion does not require cellular energy.
DIFFUSION
Graphics depicting process
of Diffusion.
http://iweb.tntech.edu/mcaprio/diffusion-animated.gif
http://www.indiana.edu/~phys215/lecture/lecnotes/lecgraphics/diffusion2.gif
***Note: solute molecules move in
BOTH directions (back & forth
between beakers until
EQUILIBRIUM
is reached– the key is NET FLOW of
solute molecules.
Rate of Diffusion of Solutes
Experiment 7.1 – Gelatin DEMO Tubes
Rate of Diffusion affected by:
• SIZE of the solute molecule
» Smaller molecules move further (faster)
» Larger molecules move more slowly
• TEMPERATURE
» Warmer temps = faster moving molecules
» Colder temps = slower moving molecules
(think about putting food into refrigerator)
OSMOSIS
• Defined: The movement of WATER
across a selectively permeable membrane.
[i.e. special kind of “diffusion”]
http://www.biologycorner.com/resources/osmosis.jpg
The Water Balance
DEMO SCOPES:
EXP. 7.4 & 7.5
of Living Cells
Higher solute
conc. outside
(e.g.
Sheep
Blood)
~ Equilibrium
Low solute conc.
outside
Higher H2O conc.
inside cell.
Higher H2O conc.
outside cell.
(e.g.
Elodea
Leaf)
http://fajerpc.magnet.fsu.edu/Education/2010/Lectures/12_Membrane_Transport_files/image014.jpg
Osmosis in Living Cells
Experiment 7.2 – “Potato Experiment”
(omit 7.2 in lab manual; see pink handout for *new* procedure)
•
Put live potato cells into 3 treatment beakers
•
H2O passes into/out of cells via
selectively permeable membrane
(e.g. plasma membrane)
– Can you predict what will happen?
•
1. dH2O
2. 15% sucrose
3. 30% sucrose
Selectively Permeable
Membranes
•
•
Experiment 7.3 – “Dialysis Bag Experiment”
Use dialysis bag to simulate cell membrane –
porous
Some molecules pass through membrane
while others do not (“selectively”)
»
Pore size prevents larger molecules from passing
through the membrane
» Molecules used in this experiment:
(1) STARCH, (2) SODIUM SULFATE,
(3) ALBUMIN (PROTEIN), & (4) SODIUM CHLORIDE.
Which molecules are the right size to pass
through the membrane?
Make predictions.
Diffusion & Osmosis Difficulties!
Don’t get bogged down trying to
memorize terms such as
hypertonic or hypotonic.
Learn what they mean & the
processes will make more sense.
CAUTIONS!!!
• Must wear gloves & goggles at all times!
» Exception: DEMO Microscopes w/ Sheep’s Blood &
Elodea
• TEST TUBE WASTE must be put into
“Waste Container”…do NOT pour down
sink!
Today’s Plan
•
Work in groups of 4 (by table). Answer questions in lab
manual as you go. All explanations of results are done
INDIVIDUALLY. Work together- answer separately!
1.
Set-up Ex. 7.2 - “Potato Experiment” (pink handout)
•
•
2.
Omit lab manual “7.2”
Monitor every 20 min. for 80 minutes = GRAPH & Explain RESULTS!
Set-up Ex. 7.3 - “Dialysis Bag Experiment” (in manual)
•
•
Let run 75 min., do chemical assay= CHART RESULTS!
Positive & Negative controls
3. Observe DEMOs
•
•
•
Ex. 7.1: Diffusion of 3 dyes at 2 diff. temps.
Ex. 7.4: Elodea (plant cells in 10%, 0.9%, & dH2O).
Ex. 7.5: Sheep blood (animal cells in 10%, 0.9%, & dH2O).
END OF LAB• Make sure to CLEAN UP your lab benches.
- Properly dispose of all items
*Chemicals into “waste container”
*Rinse residue from tubes with water
*Clean tubes into glass disposal box
-Spray with cleaner
-Wash your hands.
• WRAP UP – we will do a class “wrapup”/discussion of experimental results before
you leave today.
• Check lab manual for possible quiz questions!
Lab Next Week:
• No labs will be held on Monday, Sept. 26 or
Tuesday, Sept. 27th.
• Attend Mendel Medal Lecture on Friday,
September 30th, instead.
• Complete assignment as outlined on
handout (please take a copy before leaving
today).