If you place the potato strip in a solution where there isn’t much concentration gradient (the concentrations on either side of the membrane are the same or close) then there will be no change in size because there is the same amount of water passing through the membrane as there is passing out.
Plasmolysis is when the protoplasm in a living cell contracts while water is being removed by endosmosis. This is because the inside of the cell will shrink but the cells wall cannot shrink so the cell membrane will tear away.
Plan:
In My investigation I am going to have six solutions:
1. This beaker will contain pure water.
2. This beaker will contain a 10% sugar solution. (quite weak)
3. This beaker will contain a 20% sugar solution. (weak)
4. This beaker will contain a 30% sugar solution. (medium)
5. This beaker will contain a 40% sugar solution. (strong)
6. This beaker will contain a 50% sugar solution. (very strong)
When all the bakers are set and in place I will make sure that all the temperatures range between 24-25°C. I will then cut my potato until I have 18 strips that are averagely the same size (30mm). The strips might not be exactly the same because although I would rather have weighed them I had to measure them. Three strips will be placed into each beaker.
I will then note down the length of the strips and the temperature of the beakers in a table. Then I will place the first random three strips in my first beaker. I will keep each strip in the solutions for 20 minutes so they all get the same amount of time in the solution so it will be fairer. After the first three strips have been in the first solution for 10 minutes I will place three more strips in the next solution. When I do this I will also restart the stopwatch. So that when the stopwatch reaches 10 minutes again I will no to take the strips out of the first beaker (by this time they would have been in a solution for 20 minutes) and I will also place three new strips into another solution. I will then measure the 3 strips that I just took out and note the results in a table. I will repeat this until I finish the last beaker. Will make sure that every time the stopwatch hits 10 minutes I will repeat this task precisely until I have results for all six beakers.
Factors to control:
The Temperature of the solutions in the beakers where the potato strips are to be placed may affect my investigation. This is because in very high temperatures the potato cells could be spoiled, which affects osmosis occurring. In quite warm temperatures osmosis could speed up more than strips in a beaker close to room temperature. To prevent this from happening I will keep my solutions between 24-25°C. I will achieve this by keeping a water bath nearby.
I must also make sure that the potato strips are in the solutions all for the same amount of time. Which will be 20 minutes each beaker. This will be kept to using a stopwatch. This could affect my investigation because if the strips are in longer or for a shorter time the results won’t be reliable. This is because more or less osmosis could occur in different strips.
The size of the potato strips must be as equal as I can make it. I will measure each strip making sure that they are all 30mm although I would rather have weighed them on a scale. Unfortunately I didn’t have one. This is a factor to control because when I take them out of the solution and measure them I will not now how osmosis has affected the potato strip because the length wasn’t the same as the rest when it went into the solution, so the rate of osmosis or the difference between each strip will not be reliable.
I must make sure that none of the solutions are contaminated with anything apart from the amount of sugar dissolved into the right beakers. This may happen while mixing the solutions if the same mixing instrument is used or if a little bit of sugar spills into the wrong beaker or even if I accidentally mix the solutions up. So to prevent this I will have the beakers marked and will not put anything in the beaker if it has been in a different beaker already (when I measure the temperature I will wipe the thermometer clean first)
The same potato must be used throughout the whole investigation. Making sure all potato strips come from the same potato. This is because each potato is different and if I use different potatoes than osmosis will be different in different potatoes and the cells are different.
Prediction:
I predict that in my investigation osmosis will occur in all six beakers at different speeds. This will cause the potato strips to be bigger or smaller, turgid or flaccid when I measure them after 20 minutes of being in the solution.
In the beaker with pure water I think the potato strip will become turgid. This is because in pure water there is a high concentration of water molecules. So when a potato strip is placed in the beaker the molecules will try to evenly distribute on either side of the potato’s membrane causing water to pass through the semi permeable membrane and going into the potato. This will add to the potato’s mass to increase and causing it to swell up and become turgid.
In the quite weak solution I predict that the potato strip will increase but not as much as the first set of results. This is because there is know 10% sugar and that means that there is less water molecules to spread into the potato.
I predict that in the weak solution there might not be any change this is because now there is even less water and the concentration gradient is not as different on either side of the membrane causing nearly the same amount of water to pass through and out of the potato.
In the solutions from medium (30%)-very strong(50%) I predict that the potato strips will have a higher water concentration inside the potato so more water will leave the potato and go into the solution making the potato decrease in mass and become flaccid. The stronger the solution gets the more flaccid the potato will become and eventually plasmolysed. I also predict that in these last few beakers the potato strips will float.
Because I don’t have access to all the equipment I would like to use, this might occur in getting anomalous results and not having a fair test. I will explain more about this in my evaluation.
Equipment:
Plastic chopping board
One Potato
Thermometer
Beakers
Water
Sugar
Scalpel
Tweezers
Stopwatch
Tape Measure
Water bath (if necessary)
Preliminary Test:
Results
Each potato strip was 30mm at the start.
Note: all results have been rounded up to the nearest mm
Improvements to be made:
To improve my investigation before my final experiment is to have a sixth solution with 50% sugar to see if the potato strips will plasmolysise. I will also now use potato disks instead of potato strips so there is a larger surface area to have more space for osmosis to occur. I will also lower the temperatures closer to room temperature.
Method:
- Set out all the needed apparatus on the table
- Use a thermometer to record the temperatures.
- Make sure all temperatures are between 23-24°C
- Core a potato
- Using the cored pieces cut 18 disks that has a circumference of 20mm
- I will place 3 into the first beaker while starting a stopwatch.
- As soon as the stopwatch shows 10 minutes I will place three more disks into the second beaker
- Upon doing this I will restart the stopwatch
- When 10 minutes is again shown on the stopwatch I will restart the stopwatch.
- At this very time I will remove the first three potato disks from the beaker and measure them. I will enter the results into the table.
- I will also put three more disks into the next beaker while doing the previous two steps.
- I will then repeat the last six steps until I get 18 results from six different beakers, noting them down as I go along.
Results
Each potato strip was 20mm at the start.
Note: all results have been rounded up to the nearest mm
