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Investigation Osmosis in Potato Tissue

Extracts from this document...

Introduction

Investigation Osmosis in Potato Tissue Planning Scientific Knowledge and Understanding Osmosis is the movement of water molecules across a partially permeable membrane from a region of high water potential (dilute solution) to a region of low water potential (concentrated solution). If the water potential is greater inside the cell than outside the cell, then there will be a movement of water out of the cell. If however, the water potential is greater outside the cell than inside the cell, then osmosis will be a movement into the cell. If the water potential on each side of a cell membrane is the same, there should be no movement of water across the membrane. In equilibrium, the individual molecules travel across the membrane. The movements into the cell are balanced by movements out of the cell. This results in there once again being no movement of water at equilibrium. A cell is surrounded by a partially permeable membrane, and water may cross this membrane easily. If a cell is placed in a solution of lower water potential, water leaves the cell by osmosis. If the cell is placed in a solution of higher water potential, water enters by osmosis. When water enters a plant cell by osmosis the cytoplasm will swell, until it pushes against the cellulose wall. When water leaves a plant cell by osmosis, the cytoplasm will shrink, however the cellulose wall will continue to give some support. The stomata consist of two guard cells surrounding a central pore. The stomata open in the light and close in the dark. Each guard cell has a thick inner wall and a thinner outer wall. In the light the guard cells absorb water by osmosis and become turgid. As the cell expands, the thin outer wall bulges outwards and the guard cell curves, opening the pore. In the dark, guard cells lose water by osmosis and become flaccid, this closes the pore. ...read more.

Middle

I will ensure that they are not mixed up by tying a piece of cotton around the repeat potato cylinder, thus ensuring I can tell the difference between the two cylinders. I will also have to make sure that all the cylinders are put back in their own boiling tubes as quickly as possible and ensure that the stop watch is not started until all the cylinders are put back in their own tubes. I will vary the sucrose concentration, using concentrations of 0.0mol/dm3 (distilled water), 0.25 mol/ dm3, 0.5 mol/ dm3, 0.75 mol/ dm3, and 1.0 mol/ dm3 (sucrose solution). I think that the reason for this prediction is that when the sucrose concentration is low, the concentration of water outside the cells of the potato chips will be greater than that inside, and therefore water will move into the cells of the chip which will gain mass. As the concentration of sucrose increases, the concentration of water outside the cell will eventually become less than inside the cells of the chip, and so the water will travel out of the chip and mass will be lost. In the higher sucrose concentrated solution, the net movement of water (osmosis) is to the outside of the cell, and the chip will lose mass, the cells will become plasmolysed. In the chip in a low concentration of sucrose solution, the water moves into the cells of the chip, mass is gained, through osmosis of water into the plant cells, the cells will become turgid. I decided on all the above after conducting my trial experiments. When doing my trial experiments I used 3 values; these three values were at the very extremes of my data and also the middle value. The three concentrations that I used are: Concentration of Solution Sucrose Solution (cm3) Distilled Water (cm3) 0% 0 20 50% 10 10 100% 20 0 I collected the results for my trial experiments and plotted a graph, I thought that these results were accurate and fair and so I decided to use these values and add in concentrations of 25% and 75%. ...read more.

Conclusion

I can conclude from this anomalous graph that I need to be more careful either when conducting my results or processing my results. To change this particular procedure, I would investigate using different sizes and shapes of potato chip (investigating the effect of surface area on osmosis). I would also probably leave the chips in the solutions for a longer period of time (and so I would be able to compare the results with those of this experiment to check whether the results are different over longer periods of time). I would also probably concentrate on just one or two variables instead of all the ones that I did as I feel by concentrating on only two variables rather than several I could have improved the accuracy of all my results resulting in a more ideal graph. Therefore as further work I would investigate into the effects of the other factors that affect osmosis in potato chips and again compare my results with these and I would investigate the effect of the temperatures at which the osmosis occurred. I would also take more repeat results to improve the accuracy of my experiment. I may also use different plants or types of potato, or maybe even an adapted species of plant (xerophytes). I could also use another type of vegetable; instead of using potatoes I could use carrots and compare the way in which osmosis differs between the two; this would also be appropriate as I would be able to use the same method for this experiment as I did in my experiment. I feel that it would also be interesting to see how the age of the potato affects the rate at which osmosis happens; instead of using only one potato I could experiment using potatoes that are 2 months, 3 or even 4 months old and compare with a fresh new potato. ?? ?? ?? ?? 1 ...read more.

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Here's what a teacher thought of this essay

4 star(s)

This is a very well written and detailed report.
1. The scientific knowledge section is well researched and contains relevant information.
2. The variables section is good but the dependent variable needs to be clarified.
3. The method section is well written, although the use of two potato sections in one boiling tube may affect results.
4. The conclusion is well explained.
5. The evaluation shows a good understanding of scientific processes.
6. There are no references in this report and some of the information is clearly taken from sources.
7. Begin to give diagrams reference numbers so that they can be referred to.
**** (4 stars)

Marked by teacher Luke Smithen 08/05/2013

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