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Investigating the cellular water potential of potato cells.

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Introduction

Investigating the cellular water potential of potato cells. Aim: - to determine the water potential of potato cells by using different concentrations of sucrose solution. Introduction:- Water potential is the tendency of water molecules to move from one place to another, water potential can also be represented by the Greek letter psi, ?. The water potential for pure water is 0. This is because there is no tendency of the water molecules to move. The movement of water molecules almost always tends to be from a region of high water potential to a region of lower water potential. This is down the water potential gradient. Water potential can be affected by various factors, such as the amount of solute that is in the solution and the pressure that is being exerted. Solute potential (?s) is the amount by which the solute molecules lower the water potential of a solution. As the solute decreases the water potential of a solution, the water potential becomes more negative as more solute is added. Fig. 1 Diagram of solutions with different water potentials. In the diagram, side A has a less negative and so a higher water potential (it is closer to 0, than side B). This is as side B has a greater amount of solute molecules in it than side A, which means that the water molecules in side A have a greater tendency to move. Side B has the greater solute lower (more negative) solute potential, this is as the water molecules are less likely to move because they prefer to stay with the solute molecules. Solute potential is always negative. Pressure potential (?p) can also affect the water potential of a solution. However, instead of making the water potential more negative, the greater the pressure potential, the less negative the water potential becomes. This is as, if pressure is applied to a solution; it gives the water molecules a greater tendency to move. ...read more.

Middle

It would be impossible for me to get all of the samples to all be 100% the same in size, mass and shape. However, I can make them as similar to each other in size as possible. This is done by using the cork borer (so all samples should have the same diameter), the knife and ruler aid in keeping them the same length. If the width/length of the samples differed, then those that were longer and wider would have a greater surface area and so osmosis could occur at a greater rate. Leading to inaccurate results. The time that the potato samples are left in the distilled water for. If some samples are left in longer than others then osmosis will have had a longer time in which to occur, depending on the concentration of the solutions that the samples were left in. This may mean that the amount of water entering or leaving the cells will be greater than of the other samples. However, if some have been left in for a shorter period of time than others, then osmosis will have had less time to occur in. Meaning that the volume of water that has left or entered the cell will be lower than that of the other samples. Therefore the mass reading obtained at the end will not be the value that it should be. All the samples should come from the same potato. If some samples came from one potato and others came from another, then the investigation would become invalid. This is because the cell membranes from one potato to another will differ in their permeability as well as the cell contents. The water potential of each cell will differ somewhat. Even within the same potato, the permeability of the membranes can differ, as does the water potential of each of the cells. This will affect the osmotic movement of the water from the solution to or from the cells. ...read more.

Conclusion

As the water potential in the lower regions would have been lower than the water potential in the higher regions, this would mean that the volume of water entering the potato samples in the lower regions would have been lower compared to the volume of water molecules entering the samples in the higher regions. I believe that this is the main cause for the mass reading I obtained for the 0.4M sucrose solution that was anomalous. Whereas in the other repeats, both of the potato samples decreased in mass, the anomalous sample increased in mass. I feel that this could be the possible reason why this anomaly occurred. If I were to repeat this investigation again, I would carry out even more repeats for each of the sucrose solutions, in order to get data that is as close together as possible. By repeating the experiments many times, the results obtained are more likely to be accurate and so reliable than. Most or even all of the results should be very close to one another, any that are not close are therefore anomalous and can be seen very clearly as they will not follow the pattern that the other results will have. By doing this, I will get lower standard deviations for all of my results, meaning that my results are more accurate than the ones that were obtained when only two repeats were carried out. To extend this investigation further I could investigate the water potential of other types of potato, also I could look at the water potential of other types of plant cells, such as carrot cells, onion cells etc. I could analyse the water potentials and trends that occur in each of these plant cells and compare them to one another. I could also, do the same investigation again, only with a different set of sucrose solution concentrations, or more concentrations (e.g. 10, instead of 5). This would give me more data and so I would be able to see more clearly whether my results to this investigation were truly correct. ...read more.

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