Objectives Demonstrate diffusion across a semi-permeable membrane Differentiate between hypotonic, isotonic, hypertonic environments Examine the effects of osmosis on plant cells and.
Download ReportTranscript Objectives Demonstrate diffusion across a semi-permeable membrane Differentiate between hypotonic, isotonic, hypertonic environments Examine the effects of osmosis on plant cells and.
Objectives Demonstrate diffusion across a semi-permeable membrane Differentiate between hypotonic, isotonic, hypertonic environments Examine the effects of osmosis on plant cells and Solutions Solutions are made of solutes and a solvents Solvent is the liquid into which the solute is dissolved (ex. water) Solute is the substance that is dissolved into the solvent (ex. salt and sucrose) Selectively permeable membrane A semi permeable membrane (selectively- permeable membrane) is a membrane that will allow certain molecules or ions to pass through it by diffusion. The rate of passage depends on the: pressure concentration temperature of the molecules or solutes on either side the permeability of the membrane to each solute Depending on the membrane and the solute, permeability may depend on solute size, solubility, properties, or chemistry. Diffusion Diffusion is the tendency for molecules to spread out evenly into the available space Although each molecule moves randomly, diffusion of a population of molecules may exhibit a net movement in one direction At dynamic equilibrium, as many molecules cross one way as cross in the other direction Molecules of dye Membrane (cross section) WATER Net diffusion Diffusion of one solute Net diffusion Equilibrium Substances diffuse down their concentration gradient, the difference in concentration of a substance from one area to another No work must be done to move substances down the concentration gradient The diffusion of a substance across a biological membrane is passive transport because it requires no energy from the cell to make it happen Net diffusion Net diffusion Diffusion of two solutes Net diffusion Net diffusion Equilibrium Equilibrium Dialysis Bag Experiment prepare the Dialysis bag. put 5ml of 30% glucose solution in the bag. put 5ml of starch solution in the bag. hold the bag closed and mix its contents. Put the bag in a beaker containing 500 ml tap water and two drops of iodine solution. Record the initial color of the bag Dialysis bag Mixture of glucose+starch solution Water+K2I2 After 30 minutes remove the bag to a dry beaker label 3 test tubes: put 2ml of water in tube 1 put 2ml of the bag solution in tube 2 put 2ml of the beaker solution in tube3 Add 2 drops of Benedict’s reagent to each tube put the test tubes in boiling water bath for 5 min. Record your results Dialysis Bag Semi-permeable membrane contains Water, glucose, & starch What passes through the dialysis bag? Glucose moves through the bag to outside (as detected by Benedict’s Test) While Iodine Solution moves through the bag to inside the bag (where it reacts with the starch and give the violet color) Dialysis bag Glucose Iodine Starch At start of Dialysis At end of Dialysis Results Solution source Original contents Original color Final color Color after Benedict Bag Glucose and starch No color Blue-black Orange _ red Beaker Water + iodine Pale yellow Pale yellow Orange_ red Control H2O _ _ Blue Osmosis Osmosis is the diffusion of water through a semi-permeable membrane from an area of high water potential (low solute concentration) to an area of low water potential (high solute concentration). It is a physical process in which a solvent moves, without input of energy, across a semi-permeable membrane (permeable to the solvent, but not the solute) separating two solutions of different concentrations. Osmosis Higher concentration of sugar Lower concentration of solute (sugar) H2O Selectively permeable membrane Osmosis Same concentration of sugar cell wall freely permeable so it lets most of molecules to go through osmosis does not occur cell membrane beneath cell wall selectively permeable Tonicity Tonicity is the ability of a solution to cause a cell to gain or lose water Isotonic solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water Hypotonic solution: Solute concentration is less than that inside the cell; cell gains water Hypotonic solution Isotonic solution H2O Hypertonic solution H2O H2O H2O Animal cell Lysed H2O Normal Shriveled H2O H2O H2O Plant cell Turgid (normal) Flaccid Plasmolyzed Effect of solution on different cells Solution Concentration hypotonic animal cells haemolysis (e.g. RBC) plant cells (e.g. onion epidermis) turgid hypertonic shrink plasmolysis (cell is flaccid) Osmosis in red onion epidermal cells Prepare a wet mount of onion epidermal tissue according to the steps 1- Cut an onion bulb into quarters. 2- Remove one of the fleshy scale leaves 17 3-Fold the leaf backward to produce a ragged piece of epidermis. 4-Peel back a small piece of epidermis. 5-place the epidermis in: 0.9% Nacl solution, 10% Nacl solution, Distilled water 6-After 10 minutes, take the epidermis on a clean slide and examine. 18 and fleshy scale leaf of red onion bulb forceps epidermis What do you observe when the epidermal strip is placed in the concentrated Nacl solution ? Ans: The colored cytoplasm shrinks. fleshy scale leaf of red onion bulb forceps epidermis Explain your observation. Ans: When the piece of epidermis is placed in concentrated solution, cells lose water by osmosis This is called plasmolysis fleshy scale leaf of red onion bulb forceps epidermis What has happened to the cells in tap water ? Ans: The colored cytoplasm swells and cells become turgid. fleshy scale leaf of red onion bulb forceps epidermis Explain your answer. Ans: When the piece of epidermis is placed in tap water, cells gain water by osmosis and cells become turgid. Plasmolysis in Red Onion Cells Onion Plant cell in normal stat Plasmolysis of onion plant cell Plasmolysis: it happens when water leaves the cells by osmosis Osmosis in Red Blood Cells 1- Label 3 clean test tubes, then add 10 ml of the followings: tube (1): 0.9% Nacl solution tube (2): 10% Nacl solution tube (3): Distilled water 2-To each tube, add 1 ml of blood 3- Hold each test tube against printed paper and observe the appearance of solutions contained in each test tube. 4- Take one droop of blood from each tube and put it on a clean slide to examine under light microscope Results Solution appearance Can you read the paper Tube 1 turbid No Tube 2 turbid No Tube 3 clear Yes Isotonic solution (No change) Hypertonic solution Hypotonic solution (Blood cells shrink) (Lyses of blood cells)