Transcript Unit 8 Osmosis and Diffusion

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.
8.1.
1.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.
Photo: Jeff Beck, CCCCD
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)
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
• Observe sheep RBCs via a wet
mount of the sample
Isotonic
Crenation
Hypertonic
Cells swell
and may
burst.
http://www.msu.edu/~butter12/BS111L/Diffusion%20and%20Osmosis.ppt#263,13,Osmosis in Plant Cells
Hypotonic
RBC in isotonic solution
Plump round cells
Photo: Jeff Beck, CCCCD
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.
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
Plasmolysis
• Observe Elodea leaves via a wet
mount of the sample
•Note location of central vacuole
and chloroplasts in each sample
Hypertonic
http://www.msu.edu/~butter12/BS111L/Diffusion%20and%20Osmosis.pp
t#263,13,Osmosis in Plant Cells
Hypotonic
Animation of plasmolysis
http://ccollege.hccs.edu/instru/biology/AllStudyPages/Diffusion_Osmosis/Elodeagif.swf
Photo: Jeff Beck, CCCCD