The Effect of Osmosis on Potato Cells free essay sample

In this experiment I am going to investigate the effect of varying concentration of a differing glucose solution on the amount of osmotic activity, between the solution and a potato tuber of a given size. The purpose of this experiment is to demonstrate how living cells rely on osmosis, the diffusion of water. Osmosis is the movement of water molecules (H20) from a region in which they are highly concentrated to a region in which they are less concentrated. This movement must take place across a partially permeable membrane such as a cell wall, which lets smaller molecules, such as water, through but does not allow bigger molecules, such as glucose, to do so. The molecules will continue to diffuse until the area in which they are found reaches a state of equilibrium, meaning that the molecules are randomly distributed throughout an object, with no area having a higher or lower concentration than another. Investigation – Preliminary Experiment Strategy In my preliminary experiment I am going to be seeing how potato tubers react when placed in of 0m (distilled water) 0. 5m and 1m (glucose solution). I am doing this to gain some knowledge about how the potato tubers will be affected; so when I do my main experiment I will have basic knowledge on what will happen, this means I will be able to spot outliers more easily and learn from any mistakes which may have been made in the preliminary. Molar = (m) Mass/weight = (g) Depending on certain factors the osmotic activity between the potato tuber and glucose solution will either increase, decrease, or unaffect the mass of the potato, such as – whether the sugar to water ratio inside the potato and outside of the potato differ or not. Variables that could affect the amount of osmotic activity include factors such as: o Temperature Cells move quicker at higher temperatures, therefore the higher the temperature the higher the rate of osmosis. o Variety of Potato Different varieties of potatoes may vary in the quantity of water and/or glucose inside them. The more solution there is the larger quantity the glucose has to equalize over. o Pressure Areas of different pressure have different water potentials. o Surface area The larger the surface area, the more water can be absorbed into the cells, therefore altering the rate of osmosis. All of these factors will affect the experiment due to the nature of the potato cells, but the only variable I will be changing is the concentration of the glucose solution. Reliability Fair testing is essential in all investigations. If this experiment is not a fair test, i will obtain incorrect results, which could lead us to the wrong conclusions as they are not providing a true representation of the data at hand. Prediction My prediction is that when the potato tubers are put into the distilled water, it will increase in mass; I believe this because there are more water molecules in the water than there is in the potato cells, the water molecules will move by osmosis into the potato cells through the partially permeable membrane to create equilibrium. This means that the mass of the potato piece will increase and the potato will feel turgid. When the potato tubers are put into a high concentrated glucose solution there are more water molecules in the potato cells then in the solution; therefore the water molecules move by osmosis from the potato into the highly concentrated solution. This means that the mass of the potato tuber will decrease, and its appearance will be flaccid. The stronger the concentration of the glucose solution the more it will decrease in mass. Collecting Data Plan For this experiment I am choosing a set size for the potato tuber to be 3cm. This will ensure that it is a fair test throughout. I have also made sure that the first solution is distilled water, the second a concentration of 0. 5m and the third and final solution 1m. A potato tuber will be left in each solution for a period of 24 hours, I repeated each concentration twice times to try and get consistent results for each one. I will then work out an average of these three times, this helps to get as accurate results as possible. Results I created a graph compiled of all the evidence in the tables in a concentration (m) and mass change % (g) comparison. I have done a line graph as I believe this is the best way to portray my results accurately and clearly. Note: The graph and table have been attached overleaf. Interpreting Data Evaluating Evidence I believe that the experiment was successful as the results were as expected and were all in a similar range of one another; from looking at my graphs I can see that changing the concentration of the glucose solution affects the potato in differing ways according to the strength of the solution. The potato tuber in the 0m solution (distilled water) reacted as I expected it to, its mass increased as the concentration of glucose inside of the potato was greater than on the outside, thus the water entered the potato to try and create equilibrium. In the experiment with 0. 5m glucose solution, the mass of the potato decreased by a substantial amount, the average percentage change was -9. 53%; considering it wasn’t an extremely strong solution, it is a useful and unexpected result. The potato tuber that was placed in the glucose solution with a concentration of 1m lost even more mass than the 0. m solution; this was to be expected. The average mass change percentage was -17. 28%. This is a good result because the average of 1m is almost double the average of 0. 5m, this helps to show that the results are reliable as they follow the pattern they are expected to take. My graph and table were quite conclusive as they seemed to follow extremely closely to the line of best fit; the aero-bars are very close to the average which makes me believe that the experiment was accurate and reliable as the results are all very similar and follow the predicted ‘route’. Conclusion The potato tuber in the distilled water was the only one to gain in mass. This is because the potato became turgid as it soaked up the water molecules, by osmosis. The others decreased in mass. This is because the concentration of the solution was higher than the concentration of glucose inside the potato, this made them contract and shrink; whereas if the concentration of the solution had been lower, they would have expanded. Evaluation Generally, I think my results obtained were fairly accurate. From my preliminary test I have learnt that the three solutions were not enough, so I decided to have 6 solutions instead. This would make the graphs clearer and easier to notice any trends or patterns. During my preliminary test I also found that leaving the potato tuber in the test tube for 24 hours was not long enough to ensure that the process of osmosis was complete. So for my actual investigation I have decided to keep them in for four days, this would give the potato tuber enough time to complete osmosis as best it can achieve; it would also give me a bigger range between each result recorded. Investigation – Main Experiment Strategy Depending on certain factors the osmotic activity between the potato tuber and glucose solution will either increase, decrease, or unaffect the mass of the potato, such as – whether the sugar to water ratio inside the potato and outside of the potato differ or not. Molar = (m) Mass/weight = (g) Variables that will affect the amount of osmotic activity include factors such as: o Temperature Cells perform quicker at higher temperatures, therefore the higher the temperature the higher the rate of osmosis. Variety of Potato Different varieties of potatoes may vary in the quantity of water and/or glucose in them. o Volume of Glucose Solution The more solution there is the more the glucose has to equalize over. o Pressure Areas of different pressure have different water potentials. o Surface area The larger the surface area, the more water can be absorbed into the cells, therefore altering the rate of osmosis. All of these factors will affect the experiment due to the nature of the potato cells. The only variable I will be changing is the concentration of the glucose solution. Equipment ? ‘Number 5’ Cork Borer I decided to use this particular cork borer because it was a good size for the experiment, it wasn’t too large or too small. I needed a medium sized cork borer to allow sufficient osmotic activity to take place and for the changes in weight and length to be measured accurately. ? Potatoes of the same breed and age A reactant. The potatoes need to be the same breed and of a similar age because if a potato is old compared to another its water content could be lower.