Lab 9: Role of Membranes in Controlling Entry and Exit of Molecules to and from the Cell The Plasma Membrane • Consists of a bilayer, mostly phospholipids • Defines the boundary of the cell • Proteins allow communication with external environment – Function: 1- Selective permeability/transport 2- Communication • Membrane selective permeability * Nonpolar molecules (no charge) such as CO2 and O2 , dissolve in lipid layer and cross with ease * Polar molecules (charged) such as H2O, C6H12O6, difficult to penetrate the hydrophobic layer • Transport proteins • Channel proteins: across membrane, material specific, avoid the hydrophibic layer. Example: glucose transport channel protein are molecule specific 1- Selective transport * Passive transport: Osmosis Simple Diffusion * Active transport * Exocytosis * Endocytosis * Phagocytosis H (liquid) (Solute) L • Artificial membrane vs. cell membrane Diffusion: • Osmosis movement of solvent molecules from H to L • Simple diffusion movement of solute molecules form H to L Solvent = Liquid (water) Solute =Substance dissolved in the liquid (salt) passive transport/Diffusion Water molecules always move (osmosis and simple diffusion) * H2O Polarity, unequal covalent bond, H positive Oxygen negative A- Simple Diffusion  Is the movement of Solute (salt) molecules From H L Energy Gradient (concentration gradient) • At equilibrium molecules stop moving? • 100%. 20% salt = 20% salt and 80% water • Pure water • Pore size A- passive transport • Simple Diffusion, Solute (salt) movement Energy Gradient (concentration gradient) 100% Pore size Dynamic equilibrium after equilibrium Molecules of dye Membrane (cross section) WATER Net diffusion Net diffusion Equilibrium (a) Diffusion of one solute Net diffusion Net diffusion (b) Diffusion of two solutes Net diffusion Net diffusion Equilibrium Equilibrium • Osmosis Solvent (water) molecules movement Lower concentration of solute (sugar) Higher concentration of sugar Same concentration of sugar H2O Selectively permeable membrane Osmosis If solute molecules are larger than the pores. Water will move from low salt to high solute conc. Until solute conc. In both sides is equal. • Water balance in cells Hypertonic Hypotonic osmosis regulation in cells: Isotonic * Animal cells have osmoregulation system * Contractile vacuole Hypotonic solution H2O Isotonic solution H2O H2O Hypertonic solution H2O 60% Solute 40 % H2O (a) Animal cell Lysed H2O Normal Shriveled H2O H2O 30% Solute 70 % H2O H2O OSMOSIS (b) Plant cell Turgid (normal) Flaccid Plasmolyzed Diffusion Rate • Diffusion rate depends on: 1- Difference in concentration ➢ The larger the difference in concentration, the faster the diffusion 2- Temperature ➢ The higher the temperature, the faster the diffusion. Why? 3- MW ➢ The higher the molecular weight, the faster the diffusion of the substance in that liquid 1st Exp Today Brownian Motion You might well have studied Brownian Motion before. It is unlikely that you fully appreciated or understood it - it took Albert Einstein to really get to the bottom of it back in 1905. One of the first pieces of evidence for how gases move was discovered by Robert Brown a botanist who noticed that pollen grains in water moved about randomly. Robert Brown noticed that small grains of pollen (clarkia) suspended in water, moved in a random fashion. • Movement was only visible under a microscope. • Being a botanist he logically thought that the grains of pollen were alive. • He then tried various other small particles such as carbon (in ink) and realized that the motion was not truelly due to life. • This was the first definitive evidence that atoms or molecules existed • Movement (osmosis and diffusion) due to polarity of water molecules 2nd Experiment: Osmolarity of Plant Cells • • • • • • • Sucrose stock solution (20 mg/ml), use to prepare 4 dilutions Five, 50 ml tubes (four sucrose dilutions + H2O) Balance Five potato cylinders (~7 grams each) Incubate in H2O and sucrose dilutions Weight every 10 min for 40 min Record weight in table calculate sucrose final concentration Tube # Sucrose Stock (mg/ml) V1 H2O (ml) V2 volume 1 20 50 2 20 50 3 20 50 4 20 50 5 20 50 Sucrose Std. concentration (C2) mg/ml 0 20 Table 2: Mass of potato cores in different sucrose concentrations 0 min. 10 min. 20 min. 30 min. 40 min 30 min 40 minut H2O 20 mg/ml Table 3: Cumulative % Change (lab 1) 0 min 10 min 20 min H2O 20 mg/ml Cumulative % Change = Mass current time point – Mass time point zero Mass time point zero X 100 3rd Exp Today Transport across an Artificial Membrane 1. Open the end of the tubing by rubbing it between your fingers 2. Add 5 mL of starch solution and close the other end with a clip. Rinse briefly. 3. Fill a beaker 2/3 with iodine 4. Note the initial color of the solution in the tubing and the beaker 5. Place the starch tubing in the beaker 6. Record and explain results (final color of the solution in the tubing and the beaker) page 75 starch Iodine 3rd Exp – Simple Diffusion Through an Artificial Membrane The Case of Starch in Iodine Solution • Chemical indicator, changes its own color in presence of a specific substance • Iodine is the chemical indicator for starch Iodine I Starch Amylase (D-Glucose) SMALL LARGE • Starch and iodine are solutes dissolved in water What diffused? Why? How did you know? Is this osmosis or simple diffusion? Biology 115 Lab Fall 2018 Lab 9 Worksheet Instructor: A. Raafat _____________________________________________________________________________________ I. Student Name: Group Members: _____________________________________________________________________________________ II. Personalized Title [0.5 pts] _____________________________________________________________________________________ III. Hypotheses [1.0 pts] 1. Iodine experiment: 2. Plant cells osmolarity: _____________________________________________________________________________________ IV. Introduction IVA. General Theory/Background [1.0 pts] Page 1 of 3 Biology 115 Lab Fall 2018 Lab 9 Worksheet Instructor: A. Raafat _____________________________________________________________________________________ V. Observations & Results VA. Data [1.5 pts] Page 2 of 3 Biology 115 Lab Fall 2018 Lab 9 Worksheet Instructor: A. Raafat _____________________________________________________________________________________ VI. Discussion Questions 1. Based upon your observations in the osmolality of plant cells to sucrose, what is the tonicity of the different sucrose concentrations and water to the potato cells? Explain your answer. [1.0 pt] 2. Based upon your starch and iodine experimental results, what can you say about the permeability of the dialysis tubing with respect to the starch and iodine? Explain your answer. [1.0 pt] 3. What is/are the difference(s) between osmosis and Brownian movement? [1.0 pt] _____________________________________________________________________________________ VII. Conclusion(s)/Inference(s): [1.0 pt] _____________________________________________________________________________________ Total Score: _____ / 8.00 (Includes _____ Bonus Points for ________________________________________________) Comments: ___________________________________________________________________________ _____________________________________________________________________________________ Page 3 of 3 Table 2: Mass of potato cores in different sucrose concentrations O min. I WN 10 min. 20 min. 30 min. 40 min H20 1 * lodine diffused 4.44 4.65 4.75 4.85 4,97 into the bag 4.94 5.12 and changed 5.25 5.41 5.47 the color of 3.78 3.92 3.99 the starch to 4.06 4.13 black 4 니 5.48 5.71 5.88 5. aa 6.15 The starch did 5 20 mg/ml 4.19 4.38 4,50 4.61 4.71 not move out into the lodine and we can Table 3: Cumulative % Change (lab 1) tell because the lodine dicht change 0 min 10 min 20 min 30 min 40 minut color. H20 1 4.73 6.98 9.23 * Diffusion happened 3.64 6.28 9.51 from the beaker to the bag 3 3. 70 5.56 7.41 because the pores in the bag were 4 니 4.20 7.30 9.31 too small for the 4.53 7.40 10.02 large starch 5 20 mg/ml mereeules to pass through. Cumulative % Change = Mass current time point – Mass time point zero X 100 Mass time point zero 2 ooooo Bat Ma IVO 11
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