An Experiment to Find Out the Effect of Osmosis on Potato Cells

An Experiment to Find Out the Effect of Osmosis on Potato Cells
An Experiment to Find Out the Effect of Osmosis on Potato Cells Plan ==== Apparatus: ? A borer ? 25 test tubes ? 5 test tube racks ? 2 potatoes ? A ruler ? A sharp knife Variables: Four different sugar solutions at 10%,20%,30%and40% and distilled water Hypothesis: I hypothesis that the higher the sugar the less the potato size will increase. I think this because I think it will be harder for the liquid to get in because it is denser. Using the borer make cuts into the potato and pull out the pieces of potato. Chop the pieces so they are 20mm long repeat process 25 times. This experiment must be statistically viable i.e. the potato pieces must be identical. If you come to a bad piece of potato discard it. Put all the pieces into individual test tubes. Using one of the solutions fill up 5 test tubes to exactly the same height. Repeat process for all the solutions.
Put test tubes into racks and leave for 24 hours. This should be done as quickly as possible to ensure each piece of potato is immersed for exactly the same period of time. Research [image]Fig 1 Osmosis is the transfer of a liquid solvent through a semi permeable membrane that does not allow dissolved solids (solutes) to pass. Osmosis refers only to transfer of solvent; transfer of solute is called dialysis . In either case the direction of transfer is from the area of higher concentration of the material transferred to the area of lower concentration. This spontaneous migration of a material from a region of higher concentration to a region of lower concentration is called diffusion. Osmosis will occur if a vessel is separated into two compartments by a semi permeable membrane, both compartments are filled to the same level with a solvent, and solute is added to one side. The level of the liquid on the side containing the solute will rise as the solvent flows from the side of its higher concentration to the side of lower concentration. If an external pressure is exerted on the side containing the solute, the transfer of solvent can be stopped and even reversed (reverse osmosis). Two solutions separated by a semi permeable membrane are said to be isotonic if no osmosis occurs. If osmosis occurs, transfer of solvent is from the hypotonic solution to the hypertonic solution, which has the higher osmotic pressure. The minimum pressure necessary to stop solvent transfer is called the osmotic pressure. Since the osmotic pressure is related to the concentration of solute particles, there is a mathematical relationship between osmotic pressure, freezing-point depression, and boiling-point elevation. Properties such as osmotic pressure, freezing point, and boiling point, which depend on the number of particles present rather than on their size or chemical nature, are called colligative properties. For dilute solutions the mathematical relationship between the osmotic pressure, temperature, and concentration of solute is much like the relation between pressure, temperature, and volume in an ideal gas. A number of theories explaining osmotic pressure by analogy to gases have been devised, but most have been discarded in favor of thermodynamic interpretations using such concepts as the entropy of dilution. Results: Table 1. Shows results gained (all lengths in mm) Solution Original Length Test 1 Test 2 Test 3 Test 4 Test 5 Average Distilled water 20 21 21 22 21 22 21.4 10% sugar 20 24 22 23 22 23 22.8 20% sugar 20 20 20 20 20 20 20 30% sugar 20 19 19 18.5 18 18.5 18.5 40% sugar 20 18.5 18 18 18.5 18 18.2 Standard Deviation The most common measure of the error in an experimental quantity is the standard deviation of a set of data. The deviation of a given data point is just the difference between it and the average of the set of data. This is how to work out the Standard Deviation for distilled water and after there is a table to show all Standard Deviations together. To work out the Standard Deviation for distilled water you will need the lengths at the end of the experiment and the squares of this. Length after experiment Length after experiment squared 21 441 21 441 22 484 21 441 22 484 Total 107 2291 The equation for Standard Deviation is: Now I can do the equation: And the results for the rest of the experiments are: Experiment Standard Deviation Distilled 0.449 10% 0.748 20% 0.000 30% 0.447 40% 0.245 Analysis: (See fig 2) Increase in length suggesting that the water has diffused by osmosis across the potato membrane into the potato. The introduction of a 10% sugar solution caused the same to happen. This graph shows that when the potato was immersed in a 20% sugar solution no change occurred suggesting equilibrium. By introducing stronger sugar solutions i.e. 30% and 40% respectively we saw a decrease from the original length observed. Suggesting that the solution was moving from the potato into the external environment. Evaluation: There could be many flaws with this experiment one of the main problems is the fact that the solutions I had to work with were previously made up. There is no guarantee that the solutions are what they are meant to be i.e. the labels could have been swapped. This could have been have been stopped if we had had the time and equipment to prepare these ourselves. The results also depend on where the racks are placed if they are placed in different areas in the classroom. Some may be in the sunlight or near a radiator this would cause the temperature to rise and may cause speeding up of the process. Another problem that may have occurred is the potato may not have been cut to exactly to the same sizes. These differences may not be visible to the naked eye. Or the potato may have been cut at an angle if the person chopping was not directly over the ruler and potato. Overall I do not think these problems affected our results to a great extent.

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