1. Diffusion and Osmosis

2. Outline
• Learn the concepts of:
– Diffusion, osmosis, semi-permeable
membrane, isotonic, hypertonic, &
hypotonic
• Explore diffusion in a colloid
– Relationship between diffusion &
size 1 4
2
• Explore diffusion & osmosis in a 3
dialysis bag
– Dialysis bag experiment
– Semi-permeable membrane
– Water, glucose, starch
• Plant/animal cells exposure to
water
– Hypertonic Env.
– Hypotonic Env.
– Isotonic Env.

3. Diffusion
• Solute molecules moving from an
area of high concentration to an (water)
area of low concentration
– Random motion drives diffusion
– Movement is based on kinetic
energy (speed), charge, and
mass of molecules
1
2 4
– Equilibrium is reached when
there is an even distribution of
solute molecules
3

4. Osmosis
• Diffusion of water through a semi-
permeable membrane
– Semi-permeable: permeable to
solvents (WATER), but not to
large molecules
– High [water] to low [water]
• Dissolved molecules (i.e. glucose,
starch) are called solutes
• REMEMBER:
Water = solvent
Glucose, Starch = solutes

5. Diffusion Rates of Various Dyes
• How do different MW
solutions migrate through a 2
colloid? 1
3
• Colloid – suspension of large,
insoluble particles in a fluid
medium 6
4
– Agar plate
5
• Measure the rate of diffusion
of various dye (differ in MW)
• Measure diameter at T90  3 known(s) (crystal violet, malachite
(minutes) green, potassium permanganate)
 3 unknowns
Part 1 pg. 82

6. Diffusion Rates of Various Dyes
• How do different MW solutions
migrate through a colloid?
• Standard Curve
– Y-axis: molecular weight
(MW)
– X-axis: distance migrated
?
(mm)
Inverse Relationship
• Higher MW, slower diffusion
• Lower MW, faster diffusion

7. Dialysis Bag Experiment
• Dialysis Bag
– Semi-permeable membrane
– Water, glucose, & starch
Dialysis bag
Glucose
• What passes through the
dialysis bag? Iodine
– Glucose (Benedict’s Test) Starch
– Starch (Iodine Solution)
T0 T80
• Time Course Experiment
– Every 10 minutes, measure
the amount of glucose &
starch present in the beaker Weigh Weigh
Part 2 pg. 83

8. Dialysis Bag Experiment - Results
Lab Manual, page 84

9. Dialysis Bag Experiment - Controls
Negative control for dialysis bag experiment (performed by TA)
• Instead of using dialysis tubing, I will be using a plastic bag.
• I will determine the weight, Benedict‘s result, & iodine results at
time 0 and 80 minutes
Biochemical test controls (in pairs)
• set up test control of iodine test w/ glucose and starch
• set up test control of Benedict‘s test w/ glucose and starch
Iodine Benedict’s
Glucose ? ?
Starch ? ?

10. Effect of Water on Cells
• Hypertonic Environment
– High [solute], low [water]
• Hypotonic Environment
– High [water], low [solute]
Hypertonic Hypotonic
• Isotonic Environment
– [water] = [solute] Isotonic
Part 3 pg. 85

11. Osmosis in Living Cells
Cellulose in
cell wall

12. Osmosis in Red Blood Cells
• Observe sheep RBCs via a wet
mount of the sample
Isotonic
• Aliquot one drop the following
solutions with a ½ drop of RBC to
Crenation
a slide
0.9% saline
10% NaCl Predictions?
Hypertonic
Distilled water
• Record observation in the table
on page 85
Hypotonic

13. Osmosis in Plant Cells
Plasmolysis
• Observe Elodea leaves via a wet
mount of the sample
• Aliquot two drops the following
solutions with a new Elodea leaf
to a slide. Incubate for 10
Hypertonic
minutes @ room temp.
10% NaCl
Predictions?
Distilled water
• Record observation in the table
on page 85
Hypotonic

14. Plan of attack . . .
 Set-up Part I – Molecular Weight Diffusion in
Colloid
 Incubate for 90 minutes
 Set up Part II – Dialysis Bag
 Time course: 80 minutes (time-point every 10 minutes)
 Part III – Osmosis in Living Cells

15. Animations
Dialysis Bag Experiment
• http://ccollege.hccs.cc.tx.us/instru/Biology/AllStudyPages
Elodea Cell
• http://ccollege.hccs.cc.tx.us/instru/Biology/AllStudyPages
Osmosis
• http://ull.chemistry.uakron.edu/genobc/animations/os
mosis.mov

16. Transportation of Molecules
• Passive Transport
-Movement of molecules across a
semi-permeable membrane
- no energy required
• Active Transport
-Movement of molecules across a
semi-permeable membrane against a
concentration gradient with a
protein
- ENERGY – ATP
• Facilitated Diffusion
-Movement of molecules across a
semi-permeable membrane with a
protein
- no energy required

17. Effect of Water on RBC