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Potato / Osmosis Experiment.

Extracts from this document...

Introduction

POTATO OSMOSIS EXPERIMENT Introduction Osmosis is the diffusion of water molecules across a partially permeable membrane with the concentration gradient. This means that water molecules move from where they are in a higher concentration, to an area where they are in a lower concentration. Therefore, osmosis is always trying to make a concentrated solution more dilute. Why a partially permeable membrane is needed Molecules will always spread out as evenly as they are able to. The partially permeable membrane allows the water molecules to spread out, and thus making the concentrated sugar solution more dilute; but the non-partially permeable membrane keeps the water molecules in a compact space and prevents osmosis from occurring. AIM: The aim of the experiment is to calculate the concentration of sucrose solution that is isotonic to the cytoplasm within the plant cells of potato samples. Theory- Reasons for Prediction: I predict that the concentration of the sucrose solution will have an affect on the amount of osmosis taking place. I predict that by increasing the concentration of the sucrose solution the amount of osmosis will increase. When osmosis occurs, the previously more concentrated sugar solution gains mass (since there is a net gain of water molecules there) and the previously more dilute solution loses mass (since water molecules are leaving it to dilute the concentrated solution). During the course of the experiment, the sucrose concentration of the solution will vary so at different stages the potato sample will be the more concentrated (when it will gain mass), and it will also be the less concentrated solution (when it will lose mass). ...read more.

Middle

Not keeping the temperature the same for each test tube would cause in unfair results because some potato samples will gain/lose mass quicker than others because of the varying rates of osmosis. Temperature was kept the same through the following steps: * All the test tubes were set up in the mornings of a single week so the temperature could not have varied that much. * All the test tubes were set up in the same part of a room, so every one would receive the same amount of heat energy from the sun. If the potato samples had a varying surface area, more osmosis would occur quicker in the ones with a larger surface area; and less osmosis would occur slower in the ones with a smaller surface area. Therefore, the surface areas also had to be kept the same. This was done by using the same SOMETHING to extract potato plant samples. This meant that all the potato plant samples had the same length, diameter and height. Consequently, this action caused the mass of the potato plant samples to be near identical as well. This was shown as the masses of each potato sample were recorded using a scales machine before they were placed into the solution. Though mass is not known to affect osmosis, the fact it was kept the same did increase the accuracy of the results because there is a possibility that differing masses would have affected the rate of osmosis. During the preliminary work, I found it difficult to place the potato samples in the test tube because the potato samples were very tall. ...read more.

Conclusion

From observing the graph, it is clear to see that the circled points are clearly anomalous because they are very far away from the line of best fit. Including these readings as a part of the experiment would have negatively affected the correlation, so these results were re-done. The new results did successfully fit in with the trend of the graph. The reason why anomalies occurred, and the reason for the two variables not being in direct inverse proportion is because it was impossible to fully exclude all external factors from affecting the experiment. For example, it was impossible to make each potato sample identical in every single way; so all of them would have at least slightly different sucrose concentrations and would have individual isotonic solution values. To enhance the accuracy of the experiment, water baths, to keep each test tube at the same identical temperature, could have been used. Also, the re-weighing of the potato samples should have occurred at a set time after the experiment so some samples do not have extra time over others for osmosis to happen. To further prove the experiment was successful, I could create a solution with the concentration 0.175g sugar/1 ml distilled water using the same procedure described earlier, and then place a potato sample in it to see if there is no gain/loss. If there is no gain/loss, the experiment would have been further proved successful. If the investigation were to be re-done: * a different vegetable would be used * water baths to keep the test tubes at the same temperature would be used * more readings with smaller intervals would be used to make the line of best fit more accurate, which would then make the x-axis intercept more accurate. Qasim Chaudry 10.2 Biology Coursework Page 1 ...read more.

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Here's what a teacher thought of this essay

5 star(s)

This report of an investigation into the effect of changing sucrose solution concentration on osmosis in potato tissue is well-structured and demonstrates an excellent understanding of the processes involved.

The writer explains in detail the theory behind the experiment.

He makes good use of preliminary tests to determine the exact values he will use in the actual experiment.

The method is detailed although it might have been easier to follow if written in numbered stages.

Anomalies are identified and the readings repeated. The conclusion is based firmly on the evidence collected and is backed up by a good level of science.

All in all, an excellent effort at this level. 5 stars.

Marked by teacher Ross Robertson 10/05/2013

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