The cell membrane encloses the cell contents and regulates what gets in and out of the cell. This property of a cell is referred to as selective permeability and helps in maintaining life processes (Beckett 22). The property enables physiological process such as diffusion and osmosis to proceed.
Diffusion is the movement of particles from a region of high concentration to a region of low concentration (Roberts and Mitchelmore 38). In a cell membrane, the molecules will diffuse from the side where the molecules are more to a region where they are less. Because of selective permeability, only molecules which are small in size can pass through the cell membrane. On the other hand, osmosis is the movement of solvent molecules from a lowly concentrated solution (hypotonic solution) to a highly concentrated solution (hypertonic solution) across a semi-permeable membrane (Farine and Foss 79)
These experiments were conducted to investigate the process of osmosis in potato cells and the process of diffusion in potassium permanganate. It is hypothesized that the water level inside the potato will rise because of osmosis. On the other hand, it is hypothesized that the potassium permanganate molecules will spread uniformly in water, and thus water will turn violet in colour.
A petri-dish, distilled water, 30% salt solution, a potato, a knife and paper pins.
Create a flat surface on one side of the potato tuber by cutting with a knife
In the flat surface, create a deep cavity with a thin base left.
In the opposite side of the cavity, remove the potato skin and cut base to make the potato stable.
Pour 30% salt solution in the potato cavity up to one-third of its volume.
Label this the initial level with a paper pin.
Place the potato with the cavity side facing upwards in the petri-dish with distilled water.
Water, beaker, and potassium permanganate crystals.
1. Fill the beaker halfway with water.
3. Put some crystals of potassium permanganate to it.
4. Make observation of what happens to the crystals and the colour change of water in the beaker.
5. Leave the beaker undisturbed for some time.
Results of osmosis experiment
It was observed that the level of solution in potato cavity increases.
Results of diffusion experiment
Potassium permanganate molecules dissolve in water and move away from their high concentration region in the beaker until they spread uniformly in the water. The water in the beaker changes to violet. The colour change of water shows that the process of diffusion has occurred.
In osmosis, the solvent molecules move from a region of low concentration to a region of high concentration across a semi-permeable membrane. The water level inside the potato rises because of osmosis. Water molecules move from a hypotonic solution (where they are at a higher concentration) in the petri-dish to salt solution in the cavity where they are at a low concentration (hypertonic solution). The potato cells present between the petri dish and salt solution act as act as a semi-permeable membrane.
In diffusion experiment, molecules move from a region of high concentration to a region of low concentration until they are evenly distributed. The colour of water turned into violet at the end of the experiment as potassium permanganate molecules spread from a region where its concentration is high to the surrounding water.
Beckett, B. S. Biology: A Modern Introduction. Oxford University Press, 1986. Print.
Farine, Tony, and Mark A. Foss. Science in Nursing and Health Care. Routledge, 2013. Print.
Roberts, M. B. V., and June Mitchelmore. Biology for CXC. Nelson Thornes, 2000. Print.