This is how this theory relates to this investigation:
When the potato is in a test tube of water, the water in the tube is the high concentration, and the potato the low concentration. As osmosis is the movement of water from a high to a low concentration, the water would diffuse through the partially permeable membrane, from the high concentration, the water in the tube, to the low concentration, the potato.
When the potato is in a glucose solution, the high concentration of water would be in the potato, and low concentration would be the glucose solution. This means that the water would diffuse through the membrane, from the potato to the glucose solution.
Comparing a 0M to a 2M, I would expect the 0M to either not change in mass or cause a small drop in mass, and a 2M would cause the potato to have a large drop in mass, compared to the 0M.
As well as my background knowledge, I know that my prediction is correct from my preliminary investigation.
Before starting any planning for this investigation, I did some preliminary work to try and find out the following:
- Sizes of potato that are most suitable
- The best amount of water to use
- Which amount gave the best results, while is suitable for use in the test tubes?
- Length of time to leave potato in tube
- What length of time gives best results, but still allows enough time to do repeats and clear up in lesson?
- A suitable method and make a risk assessment of the investigation.
For the preliminary investigation, I set up 4 test tubes with water in, and put in small pieces of potato (2cm long) and I collected the following results:
This preliminary work showed that my method was correct, and that all of the measurements, such as the length of potato, the time, the amount of water, were suitable.
It also proved my theory that if water is put into a test tube with a piece of potato, then the water would transfer from the potato.
I then set up 4 more test tubes with different concentrations of glucose and pieces of potato, and collected the following results:
From these results I can see that as well as it proving my prediction it shows that my method and measurements were suitable.
Plan
Apparatus
- Potato borer and stick
- 6 test tubes
- Glucose solution
- Water solution
- Test tube holder
- Potato
- Scalpel
- White tile
- Ruler
- Balance
- Labels
- Stop Watch
- Collect a potato and us the potato borer to get 6 pieces of potato 2cm long. To get the potato to the right size, measure using a ruler and cut using a scalpel on a white tile.
- Collect test tube holder and put pieces of potato inside. Stick a label to each tube. Take out each piece of potato, measure the mass, and record in exercise book and number it on the results table, then label the tube with the same number and repeat the process with the other tubes.
- Into test tube 1, pour the correct mixture of water and glucose (see concentration table). Make sure that all mixtures of water and glucose are prepared before starting. Pour the solution into tubes 2-6, and start the stop watch for 15 minutes.
- After 15 minutes, pour out the solution, measure the mass of each potato again on the balance and record in results table.
- Repeat each concentration twice.
Diagram.
This is how I will set the equipment up.
Safety
I will consider safety in this investigation. The primary danger is the scalpel, so I will ensure that I am using it safely at all times. I will also ensure that all of the equipment is well onto the table, so it does not fall off and cause injury.
The following table shows how the concentrations of glucose will be made up:
((RESULTS ON SEPARATE SHEET ))
Graph
This is the graph I have produced to illustrate the results collected from this investigation. I can see straight away a clear trend, the results having positive correlation, as the concentration increases, the difference in mass also increases.
Conclusion and Analysis of Results
From conducting this investigation, analysing my results, putting the results both in a table and showing them graphically, I can determine that my initial prediction was correct – as the concentration of the solution increases, the loss in mass in the potato increases.
In my investigation, the potatoes in a higher concentration of glucose had a higher loss in mass, this is because the potato’s lost mass through osmosis.
Osmosis is the transfer of water, through a partially permeable membrane, from an area of high concentration to an area of low concentration.
Osmosis takes place in the different test tubes, and a higher concentration, such as 1M, which has a decrease of -10.80%, looses more than a lower concentration, such as 0.75M which has a decrease of -5.27%. This is because the higher concentration has a higher amount of sugar solution molecules than the other concentrations, and osmosis attempts to balance it out, so more water is transferred to even out the amount of water to the amount of glucose.
Evaluation
I think that my investigation worked very well, I proved my prediction and hypothesis, everything happened that I expected, and I gathered a good set of results.
Looking at my graph, I can say that the accuracy of my results is fairly high, all the points follow the trend, and all but one follow the line of best fit, the one that doesn’t has been highlighted on the graph, the result for 0.25M. There could be a number of possible reasons for this, human error for one. I could have misread one or more of the results that gave me the averages and then the percentages, leaving me with an overall inaccurate percentage.
Another possible error being the balance might not have been set to zero, or another problem with the balance, again causing inaccurate weighing either before or after the osmosis took place, leaving me with an inaccurate percentage.
Even though this investigation provided me with overall clear results, there are ways I could improve and extend the method.
To make it more accurate, I could make sure that as well as the potato being the same length, they would be exactly the same mass, and also the same surface area. I could devise a way of estimating the surface area to ensure that the experiment is in fact reliable and accurate.
I could also extend this investigation. Firstly, I could leave the potato in the solutions for a much longer span of time, perhaps even 24 hours, so the results would be far clearer. I could also extend the range of the subject beyond potatoes to other vegetables, to prove osmosis is not limited to potatoes, likewise an investigation could be made into what happens if animal cells are placed in water and other solutions.
References: In my coursework I have used information from the following sources
Edexcel modular science revision guide – book two – Richard Parsons
Scientific Background - Information on Osmosis
www.courseworkhelp.co.uk
Example of this investigation
Ideas on structure of plan
Concentrations and Measurements
www.coursework.info
Diagrams, scientific background, method information.
