Agenda• 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.

• 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.

The Paper Assignment

A Lab Report Has:• 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 1After 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!

• 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