Practical Biology Biol 101 Lab 6

1. Practical Biology Biol 101Lab 6 Hail University Faculty of Sciences Department of Biology Osmosis and Diffusion Prepared by HewidaZaki Edited by Eman El-Abd

2. Objectives Demonstrate diffusion across a semi-permeable membrane Differentiate between hypotonic, isotonic, and hypertonic environments Examine the effects of osmosis on plant cells

3. Solutions Solutions are made of solutes and a solvents Solventis the liquid into which the solute is dissolved (ex. water) Solute is the substance that is dissolved into the solvent (ex. salt and sucrose)

4. 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.

5. 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 Equilibrium Net diffusion Net diffusion Diffusion of one solute

6. 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 Equilibrium Net diffusion Net diffusion Net diffusion Net diffusion Equilibrium Diffusion of two solutes

7. Dialysis bag Mixture of glucose+starch solution 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 iodinesolution. • Record the initial color of the bag Water+K2I2

8. 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

9. Dialysis bag Glucose Iodine Starch 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) At start of Dialysis At end of Dialysis

10. Results

11. Osmosis Osmosis is the diffusion of water through a semi-permeable membranefrom 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.

12. Higher concentration of sugar Lower concentration of solute (sugar) Same concentration of sugar Osmosis H2O Selectively permeable membrane Osmosis

13. cell wall • freely permeable so it lets most of molecules to go through • osmosis does not occur cell membrane • beneath cell wall • selectively permeable

14. 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

15. Hypotonic solution Isotonic solution Hypertonic solution H2O H2O H2O H2O Animal cell Lysed Normal Shriveled H2O H2O H2O H2O Plant cell Turgid (normal) Flaccid Plasmolyzed

16. Effect of solution on different cells Solution Concentration hypotonic hypertonic animal cells (e.g. RBC) haemolysis shrink plant cells (e.g. onion epidermis) plasmolysis (cell is flaccid) turgid

17. 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

18. 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, and Distilled water 6-After 10 minutes, take the epidermis on a clean slide and examine.

19. fleshy scale leaf of red onion bulb forceps epidermis What do you observe when the epidermal strip is placed in the concentrated Naclsolution ? Ans:The colored cytoplasm shrinks.

20. 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

21. 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.

22. 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.

23. Plasmolysis in Red Onion Cells Plasmolysis of onion plant cell Onion Plant cell in normal stat Plasmolysis: it happens when water leaves the cells by osmosis

24. 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

25. Results

26. Hypertonic solution (Blood cells shrink) Hypotonic solution (Lyses of blood cells) Isotonic solution (No change)

27. Thank You