Osmosis is used in the human body and in all plants. It is how water travels around.
Equipment list
- 10 boiling tubes
- 10 identical pieces of potato (peeled)
- 0.2 m sugar solution
- 0.4 m sugar solution
- 0.6 m sugar solution
- 0.8 m sugar solution
- distilled water
- Balance
- Measuring cylinder
- Cork borer
- Scalpel
- Chopping board
- Absorbent tissue
- Test tube rack
Method
-
Measure out 30 ml of distilled water using measuring cylinder and pour into boiling tube.
- Measure out 30 ml of 0.2m sugar solution using measuring cylinder and pour into boiling tube.
- Measure out 30 ml of each sugar solution and pour into individual and labelled boiling tubes in a test tube rack.
- Use cork borer to remove 10 skinless lengths of potato from a whole potato.
- Cut each potato piece to the same length (2 cm) using scalpel and chopping board.
- Use balance to weigh each piece of potato making sure that all were the same weight to one decimal point. Record weight of each piece of potato.
- Place one piece of potato in each boiling tube (make sure all are submerged) and leave overnight.
- Remove potato pieces from solutions and allow to dry on tissue.
- Weigh each piece of potato and record new weight.
- Find difference between start and finish weight for each piece of potato in each solution.
Fair Test
Many factors could affect the fairness of the experiment. For example temperature may affect the rate of Osmosis. Here’s what I will do to make it a fair test:
- Each potato piece will start at the same weight, cut by the same cork borer in order to achieve the same surface area also. Surface area would affect the rate of Osmosis by allowing more area for the water to enter or exit. The weight of the potato will effect the results because if one potato piece is larger then another it will have more water inside it.
- Each sugar solution will be measured to the same amount for each boiling tube (30 ml).
- All boiling tubes will be kept in the same area so that no effects are made by differentiating environments.
- All water used in the experiment will be distilled and without any impurities that may effect the rate of Osmosis.
- I will repeat the experiment twice and use 5 different sugar solutions to achieve a good set of results that with facilitate my analysis.
Variables
- The range of sugar solutions used i.e. 0.2M, 0.4M etc.
Constants
- Temperature
- Start mass of Potato segments
- Measurement of sugar solution potato segments are put in (30 ml).
Safety
This experiment is not very dangerous, but the sugar solutions are sticky and messy. I must be careful using the cork borer and the Scalpel, as they are a potential hazard.
Results
Graphs of Results
Analysis
From the graph I can clearly see that Distilled water has a much larger concentration of water then the cell sap in the potato tissue. I can make this conclusion because the results show a big increase in weight of the potato piece. Meaning that water has moved from outside the potato into the potato due to Osmosis, proving that the distilled water had a higher concentration of water, as water moves from a high concentration to a low concentration.
I can also see that the glucose solution of 0.8M has a much lower water concentration then the cell sap in the potato tissue. I know this because the potato in the 0.8M solution decreased in weight by 0.5g. This means that due to Osmosis, water moved from inside the potato i.e. the higher concentration of water, to outside the potato i.e. the lower concentration of water.
From the graph I can see that both the 0.2M and 0.4M solutions are close to the concentration of the cell sap as they are both closest to 0. However I can find more accurately what the genuine glucose concentration of the cell sap is by looking where the line of best fit crosses the ‘X’ axis. The glucose concentration of the potato cell sap is 0.38M meaning my prediction was relatively close but incorrect. If I put a potato segment into a glucose solution of 0.38M, after 24 hours I would find no change. This is because the concentration inside and outside of the potato is the same so no Osmosis occurs. Instead the same number of water molecules flow in and out of the potato cells achieving ‘Net Flow’ or a ‘Dynamic Equilibrium,’ which is what Osmosis aims to do.
Evaluation
My investigation appears to have been completed fairly well. However, my results did not show a perfect pattern meaning there must have been errors in my method or most likely how I carried out the method. Errors or mistakes I could have made might be that there could have been over or just under 30ml of solution in one of the boiling tubes, or an error was made during the weighing of the potato segments.
Also the time I left the potato segments was not timed. If I had timed the experiment I could have been able to repeat it and therefore compare results, however, to do this accurately room temperature would have had to be to be monitored also as this could effect the Osmosis process. Temperature could speed up or slow down the process because more heat would mean that the water molecules would have more energy and so would move quicker and with more force.
All of my results lie fairly close to the line of best fit meaning that they are all fairly accurate. However, they are not directly on the line of best fit and so obviously small but significant errors were made. These could include slight measuring or weighing mistakes, especially involving the already prepared sugar solutions.
On my hand drawn graph I have a hand drawn line of best fit. This line of best fit determines my finding of what the exact concentration of sugar potato cell sap is. However, because my results are not all perfect this may have affected my findings.
My hand drawn graph may be inaccurate, but by creating a computer generated graph I can compare the too. Looking at the computer generated graph I can see that my hand drawn graph is fairly accurate, although the lines of best fit are slightly different. This alters my found Glucose concentration of the cell sap but still leaves me with a fairly accurate result. Improvements could be made to obtain a far more reliable result.
In order to have made my investigation more accurate I could have spent more time on making the potato segments more equal in weight, I could also have used a larger and more informative set of glucose solutions: 0.25M, 0.35M, 0.45M, 0.55M. By using a closer and narrower range of solutions, the concentration of the cell sap could be found more accurately. I could have monitored room temperature and any other environmental changes that could also affect the experiment such as light intensity. I could have done this by keeping the light intensity constant by using an electric lamp. By repeating the experiment a greater number of times my averages would be made that little but more precise.
Also to extend the experiment, because the Glucose concentration of the cell sap that I found is not entirely accurate, I could repeat the experiment but this time using a range of glucose solutions that the concentration may be. For example 0.32M, 0.34M, 0.36M, and so on. This would offer me a more accurate and reliable result to the experiment.
I also hypothesise that the experiment is still accurate if all constants are kept constant, and that if an environmental change occurs, as long as it occurs to all of the solutions in equal amounts, the results would not be altered. I could extend the experiment by proving this hypothesis.