OSMOSIS – MOVEMENT OF WATER PARTICLES
Sucrose
Water
THE POTATO CELL
Pilot test
I have decided to conduct a pilot test to check, my hypothesis is correct and to ensure I have placed a safe experiment. For my pilot test I have put three pieces of potato in three different concentration so sucrose. I have recorded their weight before and then again after a set time in the solution. I have used a formula to work out the change in weight
The formula is; Change in mass
Original mass X 100
Results
What I will use from my pilot test
I am please with my results but for my main experiment I have decided to use five solutions to give me a more varied results table. In the pilot test the potato piece were left in the solution for fifteen minutes I have decided this is a suitable time to leave the experiment. I have also realised from my pilot test that it is necessary to put my results to two decimal places. If the pilot test had not been to two decimal places, the weight of the potato would have recorded the same for both before and after in the 0.5 molar sucrose solution.
Variables
In this experiment there are a number of aspects I could change like surface area, mass and volume of solutions, time or pH level. As I want to find out the morality of the vacuole of the potato I have chosen concentration.
Apparatus list
- Potato
- Beaker
- Distilled water
- Sucrose of different morality (1m, 0.8m, 0.6m, 0.4m, 0.2m and pure water)
- Top pan balance
- Measuring cylinder
- Stop watch
- Sharp Knife
Method
I firstly must remove the skin off the potato so the skin does not affect my results. Because I don’t want to stop diffusion of water particles, I will thoroughly wash my potato before it is cut it. My potato pieces must all be of an identical size, I have decided on 4cm by 1cm wide which I will use a 30cm ruler to measure. I will cut six potato pieces in this way. I will cut one extra than necessary in case one in inaccurate. I will then mix the solutions using accurate measurements; I must weigh the potatoes before submerging them in water so I can measure the increase in weight. I will then put the pieces of potato into the solutions for fifteen minutes. Once I have removed the potato I will wait for about four minutes to allow any osmosis to take place I will then remove excess water so the weight is simply based on the potato and weigh them. I will repeat this experiment twice and then take average results to ensure the accuracy of my results.
Fair test
- The potato pieces must be from the same potato so the experiment is fair and the potato tissues are identical
- I should wait before re weighing the potato to ensure al osmosis takes place
- I will use the same equipment throughout the experiment
- I will keep the size and surface area of the potato the same. I must keep these factors the same to ensure osmosis takes place fairly in all the tissues. If the surface area was larger osmosis could take place easier.
- The potato must be totally submerged in the solution to ensure osmosis has chance to take place in all the potato
- The time must be the same for all the experiments.
- All factors need to be kept the same into this experiment apart from the solutions
Safety
Safety is an important aspect of all experiments I will take care with sharp objects and make sure the solutions are never taken internally.
Results
Analysis
I have shown my findings by producing a graph entitled ‘A graph to show the average % change in different morality’s.’ From my results, I predict that at the molarity of 0.6, the water passing between membranes will be at equilibrium. I predict this because, according to my graph, the % change will be 0 when the molarity is 0.6. I think, however, that it will be slightly less than this, maybe 0.5 because I have an anomalous result for 0.6. I have explained in my analysis why these results have occurred.
From this experiment, I can conclude that osmosis was the causes of the water movement. In concentration 1,0.8,0.6 and 0.2 (which I feel is incorrect) the mass decreases as water was drawn out of the potato but in concentration 0.4 and 0 the mass increase as water was taken into the potato. Therefore, the higher the concentration of sucrose solution outside, the greater the loss of water. The lower the concentration, the greater the gain of water. This links back to my pilot test where the results firmly show this see pilot test graph.
Evaluation
Overall I am fairly pleased with my method and results, it was a safe investigation, but I am aware they could be better. I have noticed the anomalous results, they could have occurred for any number of reasons. I may have left some potato skin on the potato cell, which could have affected the rate of osmosis. If I performed this experiment again I would check the size and the mass of each potato is the same, I have overcome this in the experiment by working out a percentage change. I think I could have repeated the experiment several more times so I had enough results to dismiss anomalous results totally.
If I were to extend my experiment I would research the rate of osmosis more closely. I would use more concentrations to give a better overall view and use potatoes that have come from different areas of land to, as the amounts of sucrose solution may be different.