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The aim of the potato slice experiment was to demonstrate the different behaviors of a plant cell in different environments and the extent of the effect on a particular environment. The importance of this experiment was to find out these properties and behaviors and put them into consideration when planting, handling or storing plants products. The process of osmosis was also to be demonstrated and observed during the experiment.
Osmosis is the movement of water across a semi-permeable membrane caused by a difference in concentration (Haynie, 2001). A semi-permeable membrane only allows the molecules of the solvent to pass through. In this case, the molecules allowed to pass are the water molecules moving from a low concentration solution to that of higher concentration. The process does not require any energy to be input but instead releases energy as witnessed when a root splits a stone or forces its way through small stones as it grows.
Osmosis therefore only occurs when a permeable cell separates two solutions of different concentrations. This can be demonstrated using an animal cell or a plant cell placed in a solution of either higher or lower concentration than of its own cell components. The cell behaves differently depending on the nature of the solution; it can lose, maintain or gain weight. A cell placed in a hypertonic solution (high solute concentration) will lose its water while one placed in a hypotonic (less solute concentration) solution will gain water. However, when a similar cell is placed in an isotonic solution, (solute concentration equal to that of cell) its weight will remain the same.
This process is important to living organisms as most of them have many semi-permeable membranes and most of the activities going on in their bodies are osmotic. Osmosis is used by the plants as they take in water through their roots necessary for photosynthesis and growth. Osmosis can at times be very harmful to the living organisms; it can cause their death as seen when a snail passes through a layer of salt. In a situation where fresh-water fish is placed in saline water or salt-water fish in fresh water, the fish die because of either cell bursting or dehydration due to their different cell components. Osmosis is therefore evidently vital to the survival of all living things whether plants or animals.
The potato slice experiment was meant to demonstrate the different behaviors of a plant cell in different environments and the extent of the effect on a particular environment.The objective of this was to get important inferences that can be taken into consideration when planting plants, handling or storing their products. It was expected that the potatoes placed in low solute concentrated solution gain weight and those in high solute concentrated solutions lose weight. This was attributed to the fact that the cells always try to attain equality in terms of concentration. The difference in weight after placement in the solutions was as a result of the potato slice absorbing or loosing water molecules (Haynie, 2001).
Materials and Methods
We were split into seven groups and each group was given a potato slice and a cylinder containing sucrose solution. Note that the sucrose solutions given to us were of different concentrations to enable us observe the effect of hypertonic, isotonic and hypotonic solutions. This was aimed at enabling us compare the rate of effect of the different solutions when they have different concentrations. Each of the groups weighed the potato slice before placing it in the sucrose solution. The weight of potato slices was different and this required us to calculate the percentage change in weight so as to make comparisons. The change in weight simply signaled the effect, but the percentage change was a good indication of the rate of effect after immersion in the solution for 45 minutes (long enough for the observations to be clear).
As shown on the table below, the potato slices 1, 2, 3 and 4 gained weight indicating that the sucrose solutions of molarity 0-0.3 were less concentrated than the potato slice cells. For example, potato slice 1placed in pure water, with an initial weight of 4.3g, had its final weight increased to 6.0g. Potato slice 5 showed no reasonable change in weight and if there was any, it was too small to be detected by the weighing machine. We made the assumption that this solution had the same concentration with that of the potato slice cells i.e. an isotonic solution. Potato slices 6 and 7 lost weight when placed in the solutions (hypertonic solutions).
|Potato No.||Initial Weight (g)||Sucrose Molarity (M)||Final Weight (g)||Percentage Change (%)|
From the above results, it was clearly seen that a plant cell increased in weight if placed in hypotonic solution and lost weight when placed in a hypertonic solution. Cells placed in isotonic solutions were found maintain a relatively constant weight.The percentage and rate of change was observed to be dependent on the concentration of the solution in which the slice was immersed. It was also observed that the percentage change in weight dropped from potato slice 1 to 4, (from 39.5 to 14.3%) and increased from slice 6 to 7.
This meant that as the difference in concentration increased, the osmotic pressure (the force per unit area of exchange required to prevent passage of water) also increased (Lenart & Flink, 1984). This in turn increased the rate of movement of the water molecules. The process of osmosis was successfully demonstrated and observed in during the experiment.
This meant that if the environment of a fresh water fish must change, then efforts must be made to avoid adverse situations that may cause instant death. The situation may even be worse if the home of a fish is progressively contaminated with a solute as it would take some time before experiencing its effect. During this window period, human beings may still be consuming the fish and they too would be in danger. This inference prompts for constant checks in our environment especially when toxic and dangerous solutions that can pass through our skin find their way to our bodies. Care should be taken at all times to avoid coming into contact with such environments.
Haynie, D. (2001). Biological Thermodynamics. Cambridge: Cambridge University Press.
Lenart, A., & Flink, J. M. (1984). Osmotic Concentration of Potato. International Journal of Food Science and Technology, 19(1), 45-63.