Work № 4. The influence of solutions with different osmotic pressure on erythrocytes and plant cells.

CLASS 1.

WORK № 1. DIFFUSION.

APPARATUSES: 50 ml cylinders of plain glass, pincers

REACTIVES: large crystals of permanganate potassium (KMnO₄), dichromate potassium (K₂Cr₂O₇), liquid silicate glue.

PRACTICE COURSE. One crystal of a stained substance is submerged to silicate glue for several seconds and then it is transferred into the cylinder that contains 25-30 ml of water. The particles of the stained substance will be gradually dissolved through all the volume of the solvent in the cylinder, while the glue will be dissolving. The solution is stained evenly by relevant colour. The rate of diffusion is inversely proportional to the size of solute molecules.

WORK № 2. INFLUENCE OF THE TEMPERATURE ON THE RATE OF DIFFUSION.

APPARATUSES: electric cooker, 50 -100 ml chemical glasses, support with tenons, glass tubes with 3-5 mm diameter and with 30-40 cm length, white stands for the glasses.

REACTIVES: crystals of permanganate potassium (KMnO₄) or another stained substance.

PRACTICE COURSE. Each of the two chemical glasses is filled by 25-30 ml of water. One of the glasses is put on the electric cooker and heated to the boiling. Then glass tubes are placed into the center of the two glasses without touching the bottom, the glasses being located on the white stands. The tubes are fixed to the support and concurrently the crystals of KMnO₄ are put down through them in each glass (with hot and cold water). KMnO₄ is very quickly dissolved in the glass with hot water forming uniformly stained solution. The diffusion in the glass with cold water runs very slowly. Try to note the time interval during which the solution will be stained similarly in both glasses.

The experience is the evidence of molecules heat movement, which testifies to the diffusion and visually demonstrates that the rate of molecules’ movement considerably increases varying with the rise of the solution temperature.

WORK № 3. ARTIFICIAL SEMIPERMEABLE MEMBRANES.

APPARATUSES: support with test-tubes, pipette with finely pulled tip, 25-50 ml chemical glasses, white stand for the glasses.

REACTIVES: 2% solution of tetrapotassium hexacyanoferrate (potassium ferrocyanide) / K₄Fe(CN)₆ /, 16% solution of copper sulphate / CuSO₄ /, on the 10% solution of saccharose. Crystals of copper, cobalt, manganese, ferrum chloride. Silicate glue with water (1:3).

PRACTICE COURSE. 1. The test-tube is filled with 3-4 ml of 2% potassium ferrocyanide solution and then a drop of copper sulfate solution is put so that the drop should be near the surface of the liquid. As a result of the reaction between the solutions of potassium ferrocyanide and copper sulfate there arises a thin clearly outlined membrane. It looks like a cell of brown colour and presents sediment of ferrocyanide copper. It turns out that the cell is a sediment membrane with its properties of semipermeability:

K₄Fe(CN)₆ + 2 CuSO₄ -------- Cu₂Fe(CN)₆ + 2K₂SO₄

The water will run through the membrane from the ambient solution to the cells because its osmotic pressure is less than the pressure of the cell. The cell will increase its size and break. The broken cell releases potassium ferrocyanide which in turn contacts copper sulfate and forms a new sediment membrane of ferrocyanide copper.

2. The chemical glass is filled by silicate glue with water (1:3) and then crystals of copper, cobalt, manganese, ferric chloride are put down into this. Semipermeable membranes of silicon acid salts of copper, cobalt, manganese and ferrum are arranged around the crystals as a result of the reaction between the dissolved glass and salts. The osmotic pressure is higher inside the cells with salts than that in the ambient solution and the solution water is absorbed by cells. New cells arise and then break and so on. You can see fanciful formations in the glass, which look like trees, algas, grasses stained differently.

WORK № 4. THE INFLUENCE OF SOLUTIONS WITH DIFFERENT OSMOTIC PRESSURE ON ERYTHROCYTES AND PLANT CELLS.

APPARATUSES: microscope, microscope slides and coverslides, test-tubes, glass sticks, preparation needles.

REACTIVES: 0.1%, 0.9% and 10% solutions of chloride sodium. Citrated blood. Onion.

PRACTICE COURSE. 1. Three test-tubes are filled by 2-3 ml of chloride sodium solution in the following way (the first test-tube -10%, the second test-tube -0.9%, the third test-tube – 0.1%) and then each of them is added by 1-2 drops of blood. The content of each test-tube is mixed and a drop is immediately taken by the glass stick from test-tube number 3 and is put on the microscope slide. The drop is covered by the over slide and examined though the microscope. The ocular of the microscope should be powerful in order to examine the drop when them is greatly enlarged. The experiment should be made in a fast way. Why? Separate erythrocytes are quick to increase in volume and destroy. This is connected with hemolysis.

After the examination of erythrocytes in hypotonic solution (0,1% NaCl) we can study the action of isotonic and hypertonic solutions produced on them. For this purpose we place drops from test-tubes number 1 and 2 on the microscope slides and cover them by over slides.

2. 2-3 ml solutions of sodium chloride of different concentrations are poured into three test-tubes. Everything is done as in the previous experiment. Pieces of thin onion film prepared by needle is put into each of the test-tubes. 10 minutes after the submerging of the onion film into the solutions they are taken and placed on the microscope slides. Then they are covered by the coverslides and examined through the powerful microscope. The films should be greatly enlarged. Now you should put your examinations in drawings and explain them.

Дата добавления: 2015-10-30