Diffusion and Osmosis

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Unit 8

• Diffusion and Osmosis

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Exercise 8.1p 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.

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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)
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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.

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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

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Ex. 8.2 Effect of solute concentration on osmosis

• Dialysis tubing will be used to simulate movement
  of substances through cell membranes

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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
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• 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?

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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.

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• 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?

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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

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Osmosis in Red Blood Cells

• Observe sheep RBCs via a wet mount of the sample

Crenation
Cells swell and may burst.
http//www.msu.edu/butter12/BS111L/Diffusion20an
d20Osmosis.ppt263,13,Osmosis in Plant Cells
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RBC in isotonic solution Plump round cells
Photo Jeff Beck, CCCCD
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Red blood cells in hypertonic solution Crenate
(spiky, not smooth edge)
Photo Jeff Beck, CCCCD
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• 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?

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Osmosis with plant cellsEx 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.

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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.

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Plants in hypotonic solution

• Vacuoles will be filled with water. This cell
  exhibits turgor.

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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?

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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

http//www.msu.edu/butter12/BS111L/Diffusion20an
d20Osmosis.ppt263,13,Osmosis in Plant Cells
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Animation of plasmolysis
http//ccollege.hccs.edu/instru/biology/AllStudyPa
ges/Diffusion_Osmosis/Elodeagif.swf
Photo Jeff Beck, CCCCD