General Biology lab Lab 6 Diffusion and Osmosis

Solution : –is a homogeneous mixture of two or more components. Solvent: – the substance present in the largest amount in a solution. Solute : –substance present in smaller amount.

Diffusion –movement of solute molecules from an area of high concentration to an area of low concentration.

Osmosis –is the movement of water across a semi - permeable membrane. –from an area of low solute concentration to an area of higher solute concentrations

Procedures diffusion and molecular weight 1.In one region of the a petri dish (upper portion ) place a few of drops of green stain (MW= 150 g/mole) 2.Then add in the opposite region, a few drops of red stain ( MW= 400 g/mole) 3.Examine what happened every 15 minutes for one hour.

Diffusion across a differentially permeable membrane 1. Fill one bag ( Dialysis membranes ) with phenolphthalein ( a pH indicator that turns red in basic / alkaline conditions ) 2. Then submerge the bag into a beaker containing sodium hydroxide ( NaOH – very alkaline solution ) Dialysis membranes –are differentially permeable ( only molecules that are small enough can pass through the membrane ).

Osmosis and Cells The movement of liquids in and out cells is dependant on the concentration of the solution surrounding it. There are 3 types of situations in which this could vary: 1.Isotonic: – Here the external solution concentration and the internal concentration of the organism are the same.

2.Hypotonic: –Here the external solution concentration is less than the concentration of the organism. –In this case water will rush into the organism. 3. Hypertonic: –Here the external solution concentration is greater than the concentration of the organism. –In this case the water will rush out of the organism.

Plasmolysis It refers to the shrinking of the cytoplasm of a cell in response to diffusion of water out of the cell. This may occur when cells are placed in a (hypertonic ) solution. Effects of Osmosis on Plant Tissues

procedure Cut 3 pieces of potato to the same size Put the first into 0% NaCL. – the second in 5% NaCl. –the third 15% NaCl. Leave them for minutes.

Normal cellsPlasmolysed cells

Effects of Osmosis on RBCs Hemolysis meaning "blood loosing" is the rupturing of red blood cells and the release of their contents into surrounding fluid Hemolysis occurs when red blood cells are placed in hypotonic solutions.

Crenation A process resulting from osmosis in which red blood cells, in a hypertonic solution, undergo shrinkage.

procedure Label three clean serological tube 1 to 3 and arrange them sequentially in a test tube rack. deliver 2 ml of each solution (Solution 0. 6M NaCl 0.9M NaCl, 1.4M NaCl) to the appropriate tube. Dispense 2 drops of blood to each tube using a syringe. Shake each tube from side to mix, then let stand for 5 minutes

Hold the rack of tubes up to the light and compare them – if the solution is transparent, hemolysis has occurred. If you are unable to see through the tube, no hemolysis has occurred and the cells should be intact. –If crenation has occurred, the appearance will be somewhat between the clarity of hemolysis and the opacity of osmotic equilibrium.