Diffusion and Osmosis

Outline

• Learn the concepts of:– Diffusion, osmosis, semi-

permeable membrane, isotonic, hypertonic, & hypotonic

• Explore diffusion in a colloid– Relationship between diffusion &

size

• Explore diffusion & osmosis in a dialysis bag

– Dialysis bag experiment– Semi-permeable membrane– Water, glucose, starch

• Plant/animal cells exposure to water

– Hypertonic Env.– Hypotonic Env.– Isotonic Env.

2

3

1 4

Diffusion

• Solute molecules moving from an area of high concentration to an area of low concentration

– Random motion drives diffusion

– Movement is based on kinetic energy (speed), charge, and mass of molecules

– Equilibrium is reached when there is an even distribution of solute molecules

2

3

14

(water)

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 = solventGlucose, Starch = solutes

Diffusion Rates of Various Dyes

• How do different MW solutions migrate through a colloid?

• Colloid – suspension of large, insoluble particles in a fluid medium– Agar plate

• Measure the rate of diffusion of various dye (differ in MW)

• Measure diameter at T90 (minutes)

1

6

5

4

3

2

1

3 known(s) (crystal violet, malachite green, potassium permanganate)

3 unknowns

Part 1 pg. 82

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

Dialysis Bag Experiment

Iodine

Glucose

Starch

Dialysis bag

T0 T80

Weigh Weigh

• Dialysis Bag– Semi-permeable

membrane– Water, glucose, & starch

• What passes through the dialysis bag?– Glucose (Benedict’s Test)– Starch (Iodine Solution)

• Time Course Experiment– Every 10 minutes,

measure the amount of glucose & starch present in the beaker

Part 2 pg. 83

Dialysis Bag Experiment - Results

Lab Manual, page 84

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 ? ?

Effect of Water on Cells

• Hypertonic Environment – High [solute], low [water]

• Hypotonic Environment– High [water], low [solute]

• Isotonic Environment– [water] = [solute] Isotonic

HypotonicHypertonic

Part 3 pg. 85

Osmosis in Living Cells

Cellulose in cell wall

Osmosis in Red Blood Cells

Isotonic

Hypotonic

Hypertonic

• Observe sheep RBCs via a wet mount of the sample

• Aliquot one drop the following solutions with a ½ drop of RBC to a slide

0.9% saline

10% NaCl

Distilled water

• Record observation in the table on page 85

Predictions?

Crenation

Osmosis in Plant Cells

• 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 minutes @ room temp.

10% NaCl

Distilled water

• Record observation in the table on page 85

Hypertonic

Hypotonic

Predictions?

Plasmolysis

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

Animations

Dialysis Bag Experiment• http://ccollege.hccs.cc.tx.us/instru/Biology/AllStud

yPages/Diffusion_Osmosis/Baggif.swf

Elodea Cell• http://ccollege.hccs.cc.tx.us/instru/Biology/AllStud

yPages/Diffusion_Osmosis/Elodeagif.swf

Osmosis• http://ull.chemistry.uakron.edu/genobc/

animations/osmosis.mov

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

Effect of Water on RBC