Turgor pressure is the amount of water that is allowed into a cell. When plants have enough water their cells can absorb it and therefore the contents of the cell begin to push against the cell wall. This gives support to the plant. The cell once full of water is called turgid.
The turgor pressure supports the leaves in a plant. However, when the turgor pressure drops within the plant cells, the leaves then drop as there is less support. When a cell looses its turgor pressure it becomes a flaccid cell.
A flaccid cell allows a lot of water to enter the cell where as a turgid cell will not allow any more water to be absorbed.
Preliminary Results
I will now move onto the preliminary work to find out if the amount of time that the solution is left for affects the amount of osmosis present. I predict that the potato will weigh more with the more time that it is given to use osmosis.
10 Minutes
20 Minutes
30 Minutes
60 Minutes
3 Hours
7 Hours
24 Hours
Summary Of The Results
As you can see from these results, my prediction was correct as when the potato was left for longer; it gave the water molecules more time to pass through the cell membrane and so therefore more osmosis was present and so my prediction was correct.
Equipment
For this experiment, I will be using:
- Potatoes
- Potato corer (no.4)
- Boling tubes
- Boling tube rack
- Scalpel
- Ruler
- Tweezers
- Scales
- Stop watch
- Cutting mat
- Measuring cylinder
- Salt solution
- Distilled water
Diagram
Method
I will cut pieces of potato to a length of 2cm and I will then weigh them. I will make sure that every piece is within 0.02g of a chosen centre point. If a potato is not within this boundary, I will discard it, as it will not give a fair result and not very accurate results. Once I have 25 potato pieces, in total, within this boundary I will record their weight onto a table of results. I will collect 5 Boling Tube racks and place 5 Boiling tubes in each rack which will contain one piece of potato and 10cm³ of salt solution and each rack of boiling tubes will have a different salt solution per rack (15 in one rack and 2% in another…).
Once the boiling tubes have stood for 30 minuets containing the potatoes, I will remove the potato and weigh it. This will then allow me to find out how much difference there is in weight between them and therefore be able to see the change through osmosis.
Fair Test
To make this experiment a fair one, I will have to:
- Make sure that the diameter is fixed by using a number 4 corer throughout the experiment
- Make sure that the boiling tubes are the same diameter and type so that I get accurate results
- Accurately measure the amount of salt solution so that the potato pieces have the same amount of solution in each test
- Make sure that the temperature of the solution is the same in each test because the temperature might affect the results and make them inaccurate. However, making the room temperature the same in each experiment will be hard to do so it is suitable to do the experiment at the same time of the year and in the same environment (i.e. Classroom)
- Time of potato in solution (make sure that the time is controlled and monitored so that accurate results are achieved)
- Length of potato (fixed to 10mm long)
Predictions
I can predict that in my preliminary results, from using my scientific knowledge, that the longer the experiment is kept for, the more osmosis will occur. I can say this because the water molecules have more time to get into the potato and so therefore, more osmosis will be able to be seen in the experiment.
I will now move onto the investigation where I will investigate how if the salt solution has a greater amount of salt in it then will there be more osmosis occurring in the solution.
Prediction
Based on my scientific knowledge, I can safely predict that the higher the concentration of the salt water, the more osmosis will occur. Therefore, as the salt solution increases the weight of the potato will decrease more in the 30 minutes of the time for the experiment. This is due to the water molecules moving from a lower concentration to a higher concentration which is the salt solution surrounding the potato.
Results
0% Salt In The Solution
1% Salt In The Solution
2% Salt In The Solution
3% Salt Solution
4% Salt Solution
5% Salt Solution
Analysis
I have noticed that there are some anomalous results from the experiments but over all there is a trend for the result pointing in the direction of my prediction previously made. Graph one shows that as the percentage of the solution increased, the weight lost increases (because the percentage changed decreases). Graph two further supports this as it follows the same pattern as graph one and so this proves that as the percentage of the solution increased, the weight lost increases. Therefore as the x axis increased, so did the y axis.
This I proved by my scientific knowledge because as the water molecules move from a higher concentration to a lower concentration of water. The potato has lost weight due to the water being withdrawn to the solution around it. When the solution increases then the more water will be withdrawn from the potato. Therefore, the turgor pressure within the potato has dropped, as there is less water within the cells of the potatoes. As the solution concentration increased, the potato cells became flaccid which may also explain why the potatoes after the experiment were not as rigid as they were before the experiment.
Evaluation
As you can see, my prediction was correct. I proved my statement with a detailed scientific knowledge and detailed graphs. As I had weighed all of my potatoes at the start to within 0.02g of a center point, the amount of results that didn’t follow the general rule (anomalies) was reduced. I only had a few anomalies so therefore my results can be seen as reliable. The quality of my results are very good as I have lots of results and they all follow the same pattern and all fit to my predictions and so therefore my results are very reliable and are good quality results.
The procedure was also very suitable, as another method wouldn’t have got such accurate results. For example, if I had of used an animal cell instead of a plant cell then the cell would have burst with too much pressure from the small water molecules. I couldn’t have changed any of the apparatus or the method to make the experiment any better as this experiment had very reliable results and so therefore there would be no need to change the method or apparatus. I could have further improved this experiment, however, by perhaps using an even more accurate form of timing as the experiment was judged on a stopwatch. From the moment the potato made contact with the solution and the moment that the stopwatch started could have had a difference between them and although this couldn’t alter the final result, as it is only a few seconds difference so this wouldn’t make much difference to the results that I have gained now but would make the experiment fairer.
To provide more evidence, I could do each experiment that I have done in this investigation three times so that I could get an average from the three sets of results that I would obtain from this to get a further accurate result.
Overall I am very pleased with my experiment and the results obtained.
By Oliver Jarvis