A small square of a red onion skin membrane was observed under a microscope at high power X40 magnification. The observation showed a large number of onion cells.
Take care with microscope slides and especially cover slips which are fragile and break easily.
Ensure students know how to deal with broken glass. If you cannot peel a layer of cells using forceps, hold a piece of onion with the red cells facing towards you and fold the tissue in the same way as closing a book. This will break the white tissue but not the red tissue. Peel off the white tissue and you should get a thin line of intact red cells on the fold line.
Cut these off and mount. Fold the top section of leaf down and crease so upper layers of leaf break, but not the lower epidermis. Peel the top section down and to the right. This should give you a single layer of pale pink lower epidermal cells.
Cut this off and mount. Ethical issues There are no ethical issues with this investigation. Procedure a If you are using a red onion cells, cut a 1 cm square of onion. Then peel off a single layer of the red cells from an inner fleshy leaf of the onion.
Cover it with a drop or two of distilled water. Add a cover slip. Replace it with distilled water added at the other side of the coverslip. Teaching notes This experiment could be run as a qualitative investigation of the effects of water and sodium chloride solution on the contents of plant cells.
You can make the investigation quantitative by using different concentrations of sodium chloride solution e. Students can count how many of a fixed number of cells are plasmolysed at each concentration.
You can calculate the percentage of plasmolysed cells and plot a graph of percentage plasmolysis against sodium chloride concentration. Cells are plasmolysed plasmolysis has occurred when the cell contents shrink and come away from the cell wall. The student sheet introduces the word, but does not require them to use it, so you do not need to explain this term unless it is relevant to your students.
Health and safety checked, September Downloads.Observing Osmosis in Potato Cells Planning Purpose: To observe the effect of osmosis on plant cells.
Hypothesis: The higher the salt content of the water, the lower the mass of the potato. Since the solute concentration of outside solution is known, one can determine the concentration of solute in potato cells by the change in weight after it reaches equilibrium A free energy-gradient for water must be present in cells for osmosis to occur.
the salt concentration in potato cell was approximated to be % by observing the. Materials Required Real Lab Procedure. Place the peeled potato on the tile and using the knife, cut both ends of the potato to make it flat. Use the knife to make a cavity at the centre of the potato from one of the flat sides almost up to the bottom.
Observing osmosis, plasmolysis and turgor in plant cells Class practical or demonstration A single layer of plant cells is placed on a microscope slide and either distilled water or 5% sodium chloride solution is added to the cells.
Discussion Being able to complete the diffusion and osmosis lab helped us better understand how diffusion (the movement of molecules from a saturated area to a non saturated area) and osmosis (the transportation of water throughout the cell) happens inside of us from the scope of a molecular level.
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