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Osmosis investigation. My prediction is that as the concentration of the solute increases, net flow will increase out the potato

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´╗┐Osmotic potential in potatoes. Introduction: Osmosis is the diffusion of water from a high concentration to a low concentration through a semi-permeable membrane. This process does not require energy (passive transport) as it works through pressure to reach equilibrium, i.e. the same concentration on both sides, and in this case the solute concentration would be equal and the solutions would be isotonic at the end- in this case there is no net flow of water through the membrane. There are two main types of solutions in regards to osmosis. e.g's -A hypotonic solution is a solution with a lower concentration of solutes compared to another. A cell in a hypotonic solution has a higher concentration of solutes than the surrounding solution, causing water to flow into the cell. Cells can burst (cytolysis) in some cases. -A hypertonic solution is a solution with a higher concentration of solutes compared to another. A cell in a hypertonic solution has a lower concentration of solutes than its surroundings, leading to a decrease of water in the cell. Water will leave the cell by means of osmosis, this can lead to plasmolysis, whereby a cell loses turgor pressure and the protoplasm (yellow in diagram) peels away from the cell wall. The effect of this is a plant will wilt if too many cells lose turgor. The factors affecting osmosis rate are: Temperature. The molecules in the solutions move faster with a higher temperature, therefore the frequency of collisions increases meaning quicker osmosis. Concentration gradients between solutes (osmotic gradient) [Basically] Because a hypotonic solution has a smaller solute concentration, there is a higher water concentration, which means there are more collisions with the membrane than the hypertonic solution causing a faster net flow to the hypertonic solution. Surface area to volume 1. A small cell has a large SA:V ratio and therefore can exchange molecules with it's external solution rapidly, because there are more H2O collisions with the membrane due to the high ratio, however the probability of successful osmosis is not increased. ...read more.


moisture and then weigh them. The reason I upped the time to thirty minutes is to get the most osmosis to have clear ranges to draw conclusions from. Once I have the results I will write them into my pre-drawn table, then dispose of the potato. Variable control: 1. The potato used- this could mean different beginning solute concentration in the potato, rendering the results less reproducible. 2. The amount of solution used- affects osmosis directly 3. The amount of time each potato will soak for- affects how long osmosis can occur for 4. The dryness of the potato when weighed- affects accuracy of results 5. The weighing scales- could mean less precise results and also less reproducible results 6. The surface area of potato- this can affect SA:V ratio in osmosis reducing reliability of results. I will try to control this by using the same weights for all the potato pieces, as they should be at least similar if they weigh the same. ________________ Risk assessment form Osmotic potential in potatoes I will be mixing sucrose solutions and using a borer on a potato. Also I will be using a scalpel on pieces of potato. Hazardous substances being used or made Nature of the hazards (e.g highly flammable, toxic) Quantities and concentrations being used or made Control measures (precautions) Spillage could be a concern in case of slipping. Slip hazard due to lack of adhesion with the floor. I will be dealing with quantities of and under 1 liter, all up to 1 mole. I will report any spillages and mop them. Any non-chemical hazards and precautions to take: Scalpels- take care when slicing, make sure fingers are clear when using a scalpel, travel the laboratory in a safe manner when holding a scalpel. Borer- when using the borer I will 'aim' it downwards into the tile that I will place it on so that I don't catch my hand with it at all. ...read more.


The extension is that it continues till all the cells lose water, which is not featured in my results. However this source also undermines my choice for a line of best fit, because I maintain that the 'dips' in the mids of the results was inaccuracy. Further data: To be surer of my conclusion I would need more investigations and results run under the improved conditions I have written about, with concentrations above 1 mole. I think this is the case because of my lack of confidence in all data sets. Summary: I still believe my prediction accounts for all the data collected, because of the beginning solutions being hypotonic thus the net flow was into the potato, this is shown in weight gain in the sucrose and sodium chloride sets and the cell water loss set, while there is no water lost which supports this. Then the concentrations jump over the isotonic stage in the two osmotic potential investigations to the point where the solution is hypertonic meaning the osmosis is faster out of the potato; this is supported by the loss of weight in the two weight experiments and the water loss in the beetroot experiment. I feel that my conclusion is quite valid due the similar trend in the other potato experiment and the similar water loss in the beetroot. Furthermore it turns out all the results had the curve which backs up my results and therefore the accuracy and validity. Overall I found my accuracy to be satisfying, despite my lack of confidence in it. I managed to explain away my only outlier and my ranges were tight meaning they could be very close to the true values. As for further work to assure me of my conclusion to the hypothesis, I would like to qualitatively observe osmosis through a microscope with multiple solution concentrations. I would also like to repeat my experiment under the improved parameters to add confidence to my results which back up the conclusion and validity of my hypothesis, because that is the theory in practice. ...read more.

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