Key factors to control
The factors I am going to control are, the size of the potatoes (3cm), I’m going to use the same size cork borer, the same amount of sucrose solution in each test tube, same amount of time left for each experiment, I’m am going to make sure that I weight the potato chunks before and after putting it in the sucrose solution, and then making sure I roll them on a paper towel before and after as well. I will put all the potato chunks and bungs (if possible) all in at the same time.
Extent and range of evidence
I am going to use 6 variables, 7 including air which is a control, and I will repeat these 3 times to make my results accurate.
Precision and reliability of evidence
I will make sure that my results are precise and reliable, by measuring out exactly 30mls of sucrose solution using a measuring cylinder, I will make sure all the potato chunks are the same size by using the same cork borer each time and measuring the length of each potato with a ruler. I will also make sure that before and after all equipment is cleaned in water, so that it isn’t contaminated for the next experiment.
Scientific knowledge
Osmosis is the movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of low water concentration. It can be affected by several different variables including concentration of sugars. In this investigation I will be exploring the effect of varying concentration of sucrose sugar solution on the amount of osmotic activity between the solution and the potato chip of a given size. Osmosis is basically a special kind of diffusion involving water molecules, which occurs when two solutions are separated by a demi- permeable membrane. The water diffuses from the weaker solution to the stronger solution. Tiny holes in the membrane allow small water molecules to pass through, but the glucose molecules are too large to pass through the demi- permeable membrane. Plant cells have a cell wall surrounding them, this is very strong. When they take in water by osmosis they begin to swell, but the cell wall stops them bursting. Plant cells become swollen and hard when they are put in dilute solutions. The pressure inside the cell will rise and eventually is so high no more water can enter the cell. This works against osmosis. But being like this is very important to plants, as it is what makes the green parts of them stand up in the sunlight. When plant cells are placed in concentrated sugar solutions they lose water by osmosis and they become weak and thin, because the sugar is more concentrated outside the plant than in the plant itself. The insides of the potato cells shrink and pull away from the cell wall; this means they may float as the potato is less dense than the solution around it. When plant cells are placed in a solution, which has exactly the same osmotic strength as the cells they are in a state between swollen and hard and weak and thin so they don’t gain or lose weight.
Diagram
Relevant information from trials
From my trials I completed in a previous lesson I chose the best amount of solution I should use is 30mls this means it totally covers the potato and isn’t enough so it fills up the test tube, I also thought the best time to leave the potato in the solution was 25mins as there was a change in mass which could be clearly seen.
Precision and skill
In my table I found that there were a few anomalous results, so I first drew a graph that represented the results including the anomalous ones and then a graph without them. To make the average of my results accurate I repeated them 3 times and then found the average. The anomalous results are highlighted in the table.
Conclusion supporting prediction
In my prediction I stated that the greater the concentration of sucrose the more the reduction mass of the potato chunk, this means that my prediction was right as my graph shows. This investigation shows simply that the more concentrated the sucrose is the more the potato loses mass, although not at the rate that if you double the concentration the mass of the potato will halve.
Detailed scientific knowledge
From my graph it also shows that the reason from my prediction was right that hen plant cells take in water by osmosis they begin to swell, but the cell wall stops them bursting. Plant cells become swollen and hard when they are put in dilute solutions which means it gains in mass, but when plant cells are placed in concentrated sugar solutions they lose water by osmosis and they become weak and thin, because the sugar is more concentrated outside the plant than in the plant itself. The insides of the potato cells shrink and pull away from the cell wall this means it loses mass.
Evaluation
Quality of evidence and anomalies
I think I had good quality evidence as I had a good range of results and I repeated them 3 times each. Although I did get a couple of anomalous results as shown from the graph, I highlighted these on the table and then ignored them and drew another graph showing a more accurate investigation. Things that could have contributed to these anomalies are; as I did the experiments on different days, the potato was different which means it might have more or less starch, and if was close to sprouting then catalysts would be released to change the starch into sugars which also means the potatoes could be in different states of health. Also the weighting machine might not be completely accurate so I might have got wrong readings, I also might not have taken each potato out of the test tube and weighed them at the same time so while they would have been laying there they could have dried a bit. Another reason that I could have collected anomalies in my results might because, potatoes hold water if that water was to come out of the potato and dilute the sucrose the potato might increase in mass instead of decreasing.
Suitability of procedure
I think some parts of my procedure was suitable for the time I had to collect my results and to make sure that everything was a fair test and each experiment was the same each time, but I think I should have left the potato in the solution for longer as then there would have been a bigger change in mass and this would have been more reliable and seen more clearly on my graph.
Changes to improve
If I was to do this investigation again I would change some of the things I did so I wouldn’t get as many anomalies, although I still think I can support my conclusion from my graph because it is scientifically correct but the things I would change would be: I would make sure I would use the same person for each experiment because I used different people to drop the potato into the solution and put the bung in so they might have out it in at different rates, this might of effected the results because people have different reaction times and this could of made a lot of difference to the results. I would make sure that next time if at all possible to do all the “result collecting” on the same day so all of the same equipment could be used, because when I did the experiment this time it was done over a couple of days and I couldn’t make sure if I was using all of the same equipment. Also might have been unable to completely sterilise the test tubes after it had been in contact with the sucrose solution, this may have made my results unreliable. All these could have contributed to the couple of anomalies I collected.
Further work
If I was to extend this piece of coursework I could increase the surface area of the potato and cut it up into discs of potato as this might increase or decrease the mass quicker than it would in a chunk, I could then compare the reactions rates of the two experiments. Increasing the surface area the more chance there is of more frequent, successful collisions of particles so the rate of reaction would be faster.
Diagram
More surface area Less surface area
I could also find out the concentration in a potato (cell sap), by using more specific concentrations of sucrose to get the exact level in a potato, because the potato will not increase or decrease when the level of the solution is exactly the same as the level of the potato, in my experiment one of the experiments didn’t change but this was because I didn’t leave the potato in the solution long enough.
