Unit 8 Diffusion and Osmosis

Exercise 8.1 p 109 Examine two factors that affect the rate of diffusion –Temperature –Molecular weight We will look at the movement of two dyes as they diffuse through an agarose gel.

Obtain petri dishes with agarose. 2. Punch out 2 wells with a straw. This is to make a depression in which to place the dye. 3. Put a drop of potassium permanganate in one well and a drop of Janus Green in the other well. 4. Incubate one plate at RT and one plate on ice. 5. At 15 minute intervals measure the zone of diffusion around each well (Measure diameter of the ring) Photo: Jeff Beck, CCCCD

Osmosis Specialized type of diffusion involving diffusion of water molecules. Movement of water molecules from an area of higher water concentration to an area of lower water concentration.

Dialysis tubing Differentially permeable material Has certain pore size that only allows molecules smaller than the pore to pass through. Larger molecules cannot pass through. Dialysis tubing simulates the plasma membrane. Inside the bag- inside of cell Fluid in beaker- outside of cell

Ex. 8.2 Effect of solute concentration on osmosis Dialysis tubing will be used to simulate movement of substances through cell membranes

Prepare tubing by tying one end with string, pipetting liquid into bag, then tying other end with string. Trim off excess string. Photo: Jeff Beck, CCCCD

Set up 5 bags and 5 beakers with the solutions described in the lab manual. Weigh bags before placing in solution in beaker. Re-weigh bags at 20 minute intervals (pat bags dry before weighing) Determine which bags gained or lost weight. Were bags placed in iso-, hypo-, or hypertonic environments?

Ex 8.3 Differential permeability of membranes The dialysis tubing contains microscopic pores of a certain size. Only molecules small enough to go through pores can pass through the membrane. Set up a beaker with a dialysis bag using the solutions as described in the manual.

Incubate for 1 hour, then test the beaker contents for –Starch (iodine test) –Chloride ion (silver nitrate test) (Special disposal) –Sulfate ion (Barium chloride test) (Special disposal) –Protein (Biuret test) Which molecules passed through the tubing and into the beaker? Why do you think some molecules but not others passed through the tubing?

Diffusion/Osmosis in Living Cells 8.4A Osmosis with Red Blood Cells Demo microscopes set up in back for you to view and draw what you see in Table 8.5

Osmosis in Red Blood Cells Isotonic Hypotonic Hypertonic Observe sheep RBCs via a wet mount of the sample Crenation in Plant Cells Cells swell and may burst.

isotonic RBC in isotonic solution Plump round cells Photo: Jeff Beck, CCCCD

hypertonic Red blood cells in hypertonic solution Crenate (spiky, not smooth edge) Photo: Jeff Beck, CCCCD

RBCs in hypotonic solution –Cells may not appear as they have burst View a page of text through each of the tubes of blood. Can you read the text?

Osmosis with plant cells Ex 8.4B Instructor will set up wet mount demo of Elodea leaves One will be soaked in hypertonic (20% saline) solution One will be soaked in distilled water (hypotonic). Definition of turgor pressure is the pressure of the cell contents against the cell wall.cell cell wall

Plant cells in hypertonic solution Plant cells have rigid cell walls Vacuole will lose water and plasma membrane will pull away from the cell wall. This is called plasmolysis.

Plants in hypotonic solution Vacuoles will be filled with water. This cell exhibits turgor.

Elodea cell in hypertonic and hypotonic solutions Hypertonic- –Chloroplasts will be concentrated at the center of the cell. –Why? Hypotonic- –Chloroplasts will be distributed around the edge of the cell, or distributed evenly throughout. (Not concentrated in one place) –Why?

Osmosis in Plant Cells Observe Elodea leaves via a wet mount of the sample Note location of central vacuole and chloroplasts in each sample Hypertonic Hypotonic Plasmolysis t#263,13,Osmosis in Plant Cells

Animation of plasmolysis Photo: Jeff Beck, CCCCD