Transcript
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.
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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
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(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)
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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
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