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Biology Coursework: Osmosis in Potato Cells

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Introduction

Biology Coursework: Osmosis in Potato Cells Introduction We are going to investigate the process of osmosis in potato cells. Osmosis is the diffusion of water from a lower water potential gradient to a higher water potential gradient through a partially permeable membrane. We will use varying concentrations of sucrose solution and observe the effects they have on the potato. Prediction I perceive the higher the concentration of sucrose solution, the lower the weight of the potato sample will become, as the water leaves the potato's cells to balance the water potential gradient, in contrast if the solution is too dilute, then the potato will take in water and gain weight. "We know that osmosis the flow of one solvent, (water) of a solution through a membrane while the other constituents are blocked and unable to pass through the membrane. Experimentation is necessary to determine which membranes permit selective flow, or osmosis, because not all membranes act in this way. Many membranes allow all or none of the constituents of a solution to pass through; only a few allow a selective flow. As the potato is a plant cell, it contains a vacuole and a cytoplasm. The cell membrane is also partially permeable i.e. it lets some substances in but not all substances. This means that water paeticalscan diffuse into cells by osmosis if the cells are surrounded by a weak solution. (Osmosis is the movement of water molecules from a high area of water potential to an area of low water potential through a selectively permeable membrane.)" Planning To ensure a fair test the following must be considered: * Temperature - the potato may take in more or less solution if the temperature varies, the temperature I will use is room temperature. Under school conditions this should remain constant as we have central heating on a thermostat but there is still room for error. ...read more.

Middle

4.88 g " 4.48 g 1.5M 4.96 g 4.99 g " 5.12 g 4.55 g " 5.22 g 4.71 g 2.0M 4.11 g 4.90 g " 4.24 g 5.00 g " 4.40 g 4.98 g Analysis The results compiled are wholly unreliable because there is dramatic difference between the values. The one thing that does fit with my hypothesis in the cooked potato is that it took in more water than that of the raw potato, this indicated by the cooked potato having a steeper line on the average of averages experiment graph. Usually anomalous results are incorrect, but the circle in yellow indicate the anomalous results from each graph of cooked and uncooked potato but, these do tally with my predictions with scientific theory in mind. The connection between osmosis should be the inverse of concentration, as osmosis decreases the concentration should increase, not osmosis increasing with concentration. The graph should also be a parabola not straight, because osmosis and concentration aren't proportional there is no rate of anything, there is no formula that states for n concentration, there is y weight change. The first graph of initial results shows a curve for the cooked potato, which is the right kind of graph but does not match science! If the results graphed were reflected in the negative y-axis they might be believable because osmosis should decrease as concentration increases. At first glance at my results table I wondered if I'd recorded the results for 'after' in the 'before' column but this is consistent throughout the whole table so I don't think I'd make a huge mistake and keep making it. Conclusion Our results are inconclusive, and the findings cannot be held as reliable. If a graph is plotted from the two anomalous results it produces a graph more believable, however more points really are needed because a straight line through one point is not convincing evidence. ...read more.

Conclusion

Again, if more time was allowed this wouldn't happen, or it more balances were available stationed around the room. If the enquiry were to be repeated I don't think I'd recommend a potato because it is too fiddly (an irregular shape) difficult to cut and there is too much room for error, but if it was possible with the sufficient time and more careful planning and accuracy, salt solution could be used instead of sugar to see if this produced the same results as sugar and verifying the hypothesis that osmosis will occur. If osmosis really does occur when one water gradient is less than another, the trend should be evident with any substance soluble in solution. We could even change the type of potato to see if all potatoes behave the same during osmosis, providing we conduct the experiment correctly. Even better, a vegetable that is easy to cut such as a cucumber, something already cylindrical and repeat the investigation on that. (I do realise it isn't a prism throughout, so some would be wasted but cutting round it could be easier. Cutting round an object could cut a set diameter.) A circle would maximise surface area and encourage osmosis and at least the slice would lay flat say in a petri dish and be completely submerged producing a more accurate result. I also know that cucumbers have high water content so any change should be more apparent. Another theoretical way to observe osmosis is to stain celery, because it takes up dye through it's xylem tubes and then see if this dye moves out into the solution, it probably isn't practical but it is only an idea. However you propose to discover osmosis in potatoes there is always room for human error and under classroom conditions and limitations in time, (which we needed more of) to complete our experiment to the standard of something substantial proving or disproving my hypothesis is very difficult. Elisa Holbrook P1 ...read more.

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Here's what a teacher thought of this essay

3 star(s)

A very well planned investigation of osmosis. However, it was not conducted entirely as planned. Analysis of the experimental method is good but some analysis of data is weak.

Marked by teacher Adam Roberts 14/03/2013

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