Agenda
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Collect Pre-lab #5 – Diffusion.
Lab quiz #4.
Lab 5 Today on Diffusion & Osmosis.
Microworld samples for today: sheep blood
and Elodea?
• Paper Assignment due next week!
• In 2 weeks you will also design an experiment
on fermentation.
The Paper Assignment
• Obtain the Paper Assignment from either your instructor
or the lab web page. It is an assignment to help you
understand the makeup of a scientific paper or article
• It is due in a week.
• Follow the directions and then answer the questions.
• In two weeks you will make an Informal Lab Report on an
experiment you will design with
your lab group.
A Lab Report Has:
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A Title
An Introduction section
A Materials and Methods section
A Results section
A Discussion (or discussion/conclusion) section
A References (or Literature Cited) section
– See an example report in Appendix A of your lab manual
• Your Paper Assignment should help you learn the above
and help you understand how to write an informal lab
report which you will do in 2 weeks!
Experiment 1: Diffusion of molecules
through a selectively permeable
membrane
• Dialysis tubing =
selectively permeable
membrane
• Permeability based on
molecular size so it
differs from the
permeability of a cell
Experiment 1: Diffusion of molecules
through a selectively permeable
membrane
• Secure one end of the
dialysis tubing by tying it
with string
• Add 4 pipettes full of
glucose to bag (5-10 ml)
• Add 4 pipettes full of
starch to bag (5-10 ml)
• Remove air & tie the bag
shut. Helps if two work
together.
Experiment 1
• Wash the bag well.
• Dry it and record its weight.
• Place in beaker containing
water and several droppers
full of iodine.
– What does iodine test for?
• Monitor for color change
over 45 minutes.
Glucose
solution
Experiment 1
After 45 minutes:
• Make observation about starch
diffusion.
• Wash & weigh the bag, testing
for osmosis.
• Perform Benedicts test on
solution in the bag, and in the
beaker to test for glucose.
Glucose
solution
Exercise 2 – Brownian Motion
• Using Carmine Dye to observe Brownian motion
• Is a powder of particles that are tiny enough to move
when a water molecule collides with them.
• Best if you use a nearly invisible amount
• Handle w/ care, Carmine Dye
tends to go everywhere!
Exercise 3: Osmotic Activity in Plant Cells
• What’s different about plant & animal cells?
• The cell wall protects a cell in hypotonic soltions.
• Observe plant cell under 4% salt solution, best to
observe as you add the salt and see what happens!
• WASH & put slides
away!!
Exercise 4: Osmotic Activity in Animal
Cells
• Put blood cells in different
solutions of salt.
• Observe cells IMMEDIATELY
after placing in each
solution!
• NOTE: Blood needs to be in
fridge when not in use.
• NOTE: Dispose of blood
slides in bleach solution!
Exercise 5: Molecular Weight DEMO
• At my desk there will be an agar plate with a drop
each of 1.5% potassium permanganate and 3.5%
methylene blue.
• Observe after 30 minutes to 1 hour to compare the
effect of molecular weight on diffusion.
• Which do you expect to move faster, the bigger or
smaller molecular weight? Which is smaller?
• One problem w/ this experiment is that they are at
different concentrations. Which dye do you expect
to diffuse faster by the concentration?
Using the Oil Immersion Lens Today!
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Start focusing using lowest power (4x)!
Switch to the next higher objective
Do NOTuse the Coarse Focus Knob after 4x!
Use ONLY the Fine Focus Knob to bring the slide into
focus!
• Continue this procedure till you come to 100x
Using the Oil Immersion Lens
• To add oil, move the lenses half-way between 40X
and 100X lenses
• Add a very small amount of oil (less than 1 drop)
• Click the 100X objective into place
• Do NOT move back to 40X, or you’ll get oil on it!
• If using oil, you must clean it
• Use only lens paper &
lens cleaner on lenses!
• Oil has a similar refractive
index as glass
• Keeps light rays from
bending going through
sample
• Increases resolution
• 100x w/o oil is worse than
the 40x