Demonstration of Osmosis using living cell
Aim:– To demonstrate the process of osmosis using a living tissue e.g. Yam or Pawpaw
Method: Two thick slices of yam A and B are obtained and their skin peeled off. A large cavity is drilled into the middle of each. A strong solution of salt is poured into A. Yam slice B is left without salt to serve as a control. They are both kept in a trough containing distilled water and allowed to stand for some hours.
Result: After some time, it is observed that the water level in yam slice A rises tremendously while no water rise is observed in B. Water molecules moved from the rough yam slice A
Conclusion: It can be concluded that living tissue have semi-permeable membrane which allows molecules to pass through from the surrounding if they have higher osmotic pressure. Water could not move to Yam slice B since it contained no salt or sugar solution. It is therefore of the same osmotic pressure with the water in the trough
Experiment to demonstrate osmosis using a non-living material
Aim: To demonstrate osmosis using non-living material
Method: A piece of cellophane packet is tied over the mouth of a thistle funnel carefully and tightly. The cup of the thistle funnel is filled with sugar solution while the beaker contains water.
The cup side carrying the semi-permeable membrane is immersed into the beaker of water, the experiment is left for one day. The control experiment is similarly arranged but instead of filling the funnel with sugar solution it is filled with water.
Result: After few hours the level of liquid in the funnel has risen to its original marks. There is no rise in the control experiment.
Conclusion: Water has passed through the semi-permeable membrane to the sugar solution by osmosis (endosmosis)
Biological Significance of Osmosis
Osmosis is a special form of diffusion. Diffusion allows free movement of substances without hindrance, but osmosis because of the selective permeable membrane allow some particles to pass through them while other cannot. All living cells have cell membranes which are selective to control or select which substances of outer or leave the cell.
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