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Estimate the concentration of the cytoplasm of potato cells.

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Osmosis Coursework Introduction The investigation which I am going to be carrying out is to estimate the concentration of the cytoplasm of potato cells. I will do this by investigating using the movement in and out of the potato cells through Osmosis. Osmosis is the process whereby water molecules pass through a semi-permeable membrane from a high concentration to a low concentration until an Osmotic equilibrium is reached. So it is like a special form of diffusion. Plants take up water from the soil, through their root hair cells by the process of Osmosis, and they continue to use Osmosis from cell to cell to transport water up the plant. Plants have many uses for the water they take up by Osmosis, one main importance being to maintain the plants structure by keeping them upright and turgid. As in plant cells, they have a special containment area for water called the vacuole, when the vacuole is void of water, the cell will become flaccid and loses its shape. When enough water has been lost the cell will begin to retract and pull away from the cell wall. When this occurs the cell has been plasmolysed. However when a plant has a good water source the vacuole will take up large quantities of water and become turgid. This turgidity is essential for plants as it is this that plants rely on to keep them upright and maintain their structure, this is where the plants unique traits of having a cell wall help the cell to avoid from rupturing, as the cell wall which is a cellulose based structure is extremely strong and can provide enough resistance to hold the cell together. As the cell becomes turgid and pushes outwards, the cell wall pushes back with an equal opposing force. This is why animal cells are not well adapted to take up water, as they have no place like the vacuole to store it as plant cells do, and they have no cell walls, so when they take up to large a quantity of water, they will rupture. ...read more.


Bad Points I have quite a few criticisms of my method, as now that I have looked back I can see that my method is quite flawed, as throughout my experiment I did not measure the volume of the salt solutions that I was putting into the Petri dishes, as that way I could've made them all the same. Also because I only put a shallow pool of water at the bottom of the Petri dish I did not manage to fully submerge any of my chips, so the possible surface area for absorption was decreased. The surface area and width of my chips were also drastically different from one another, so some would have had a larger surface area than others again giving some chips an unfair advantage. Another bad point of my experiment is that my Petri dishes were left uncovered, this means that some evaporation may have occurred. The timing of the experiment was not very good as all the chips were removed and placed in one-by-one so some had a longer time of exposure than the others. The final criticism I have is how I measured the chips, as the length is an inappropriate measurement of the rate of Osmosis as the chips not only elongate but expanded as well and we did not take this into consideration that the width will increase as well, also the chip may take water in without any outwardly physical signs like an increase in length, however if I were to measure the length again then I would use a calliper. In my main experiment I will change the following aspects: * I will increase the period of the chips submergence, in order to ensure that osmotic equilibrium is achieved in all the solutions. * I will measure using weight instead of length, as the chips will expand as well as elongate, whereas the weight will give a measurement of all the water lost/gained. ...read more.


The clock we used was also unreliable, as I believe that if we were to have used a computerized clock the timing would have been much more reliable and accurate, as with a computer the power supply is constant all the way throughout, whereas with a battery powered clock slowly the power source decreases and the clock will gradually slow down, so the timing may not have been precise and the chips may not have been able to reach osmotic equilibrium. I think that if the experiment was to be repeated then I would perhaps use Visking Tubing however I realized that this would defeat the whole purpose of the experiment as it is to find the average concentration of the cytoplasm of the potato cells. However if there were some way in which I could incorporate this in to my experiment then it would be usefuls there would be little to no variation between the Visking tubing unlike the potato chips. So if I were to repeat this experiment I would: * Use an electronic clock for more accurate readings * Use tweezers to remove and place the chips into the solutions * Make sure that I quickly weigh all of the potato chips immediately after the time limit is up * Ensure that the room temperature is the same on both of the two days or perform the experiment in a room where the temperature is monitored * I would ensure that all of the potato chips surface are were identical in area. Conclusion Overall my experiment was successful, as in the end I was able to draw a decent graph that showed a clear trend in the data and allowed me to draw a line of best fit. Although my experiment was not perfect and there were a few anomalous results, I believe my experiment was successful. My prediction has also been proved by my experiment and I have discovered the average concentration of the cytoplasm of potato cells and it is 0.12M. ?? ?? ?? ?? Thomas Bartlett Biology Ms Amboule ...read more.

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