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

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 (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 = solvent Glucose, 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) 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 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 IodineBenedict’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 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 Pages/Diffusion_Osmosis/Baggif.swfhttp://ccollege.hccs.cc.tx.us/instru/Biology/AllStudy Pages/Diffusion_Osmosis/Baggif.swf Elodea Cell Pages/Diffusion_Osmosis/Elodeagif.swfhttp://ccollege.hccs.cc.tx.us/instru/Biology/AllStudy Pages/Diffusion_Osmosis/Elodeagif.swf Osmosis smosis.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