In our investigation into osmosis with plant tissues we have chosen to use a potatoe, due to its availability, price and consistency. We are going to be using potatoes in a sucrose solution, so that we can control the concentration of water being used each time. I have done some research from the book biology: a functional approach written by MBV Roberts, and a potatoe has 0.27M sucrose solutions within it.
Aim
To investigate how osmosis relates to different concentrations of sucrose solution inside and outside of a plant cell.
Hypothesis
I believe that when the potatoe is placed in a sucrose solution with a higher or lower concentration of water than it, the percentage mass change will go up very rapidly. However after a short period of time the speed at which it changes will curve of if you will and the percentage mass change will slow down, due to the pressure inside the cell, which builds up gradually.
Percentage mass change
However we will see slightly different things happening when the concentration is higher and lower. When the concentration of water is higher than that of the potatoe, the potatoe will fill with water and become turgid, the cell however will not burst, as the cell wall is too strong. But when the concentration is lower than that of the potatoes the water will diffuse out of the potatoe into the sucrose solution, thus leaving the cell flaccid.
Rate of reaction
Molarity
I also believe that the rate at which osmosis occurs is proportional to the concentration of water. As you can see from the graph, as the difference in concentration between the solution and the potatoe increases, as does the rate at which the reaction occurs.
Method
We will perform one trial experiment to try and determine the most efficient method of performing the experiment and then we will do the real thing.
We will take a cylinder of potatoe from the potatoe, and cut it into a separate cylinder. We will then put three measured cylinders into six jar specimen bottles and add sucrose solution into each jar (jar one was 0M-distilled water ranging to jar six-1M sucrose solution) we will then weigh each piece of potatoe every 15 minutes for an hour, cleaning each piece of potatoe.
We assume that this means that the pressure and temperature in each case is the same, as these are factors which could affect osmosis, and we know that the volume, size and surface area of each cylinder is the same, and as they are all from the same potato, the only variable that we are altering is the concentration of the solution.
When conducting the experiment we need to remember to keep it a fair test, whilst doing so we need to consider these things:
-Keep the potato samples the same length (2cm). This is because if one potato sample is 1cm long and one is 3cm long then the 3cm long sample will have a larger surface area and osmosis will occur much faster
-Average: To make the experiment as accurate as possible an average will be taken out of 3 results for each solution taken. This is so that we can determine which results are accurate and which are anomalous.
Trial experiment
In the trial experiment, we discovered that our original experiment plan wasn’t quite as good as it could be, and this was true for many reasons. We found that the change over between each sample (as we did each one twice) needed a lot more time, and maybe instead of doing three at a time we could have a time break between each one. We cleaned everything up before and after each weigh in but I feel that we must have done something quite wrong with some of the pieces, as the results they have given aren’t very accurate. We also needed to use smaller pieces of potatoes, as they were quite hard to pick up and put back with the forceps and we kept on missing them etc. I also feel that to remove anomalous results it would be a lot scientifically sounder to do each sample three times instead of twice cause then we can make rule out the anomalous result. Another possible problem was that with the 1m sucrose solution the potatoe was floating and not all of it was submersed in liquid so not as much surface area was being used in osmosis so the rate of osmosis probably wasn’t as fast.
Result
Raw data
Transformed data
Conclusion
From these results I can conclude
Evaluation
I believe the experiment was a success as you can see from the results and conclusion most of my results stayed true to my hypothesis apart from one or two anomalies, I believe this is because we had a trial experiment which we could trial out which methods worked and which didn’t, and sing this we could develop the fairest way of obtaining good results and thus the optimum experiment. We did however pick up a few anomalous results along the way, the 0.8 molar experiment didn’t go quite as well as all the others, the reason for this was half way through the experiment one of the members of a neighboring group knocked it over, this affected the results quite a lot as we had to get completely new 0.8 solution which as you can see speeded up the rate of reaction towards the end so the results were unfair. The experiment however apart from certain knocking over incidents was fairly reliable, as long as you considered all the factors that could affect the test and all the precautions you needed to take to make sure it was a fair test the experiment was very reliable. There were however a few limitations, mostly to do with equipment; there weren’t nearly enough weighing machines, ergo mass pile ups were cause queueing to use them and times were occasionally missed by some groups, what would have made this much easier would have been to have a mass cooperation from each and every group as to which times and when they could use the weighing machines. There could be a few improvements made for this experiment, what we could have done is have lots of different groups doing one molarity each however lots of times, this would have created much more accurate results and eliminated anomalous results. Another thing that I would like to do is alter all the factors, e.g. size, surface area, temperature and also try it with not only different vegetables but fruit as well. I could also then vary the solution, e.g. instead of sucrose use another liquid substance present in fruit and vegetables. Apart from this I feel the experiment was highly successful and thoroughly enjoyed.
