Prediction: The aim of this investigation is to explore osmosis in potato cells and find the concentration of sucrose within. The osmosis will be taking place across the partially permeable membranes of the potato cells. It can be predicted, from previous knowledge, that the sucrose concentration in a healthy potato cell is approximately 10%. Therefore, any concentration that is weaker will add water to the cells, causing them to become turgid and increase in mass, and any concentration that is stronger will remove water from the cells, causing them to become flaccid, and decrease in mass. At a solution strength of approximately 10%, it can be predicted that little osmosis will occur due to the similarity of the solutions inside and outside of the potato cells.
Variables:
Independent: Sugar concentration of solution, varying in range between 0% and 50%
Dependant: Mass of potato chips
Controls:
Temperature of solution,(Because any change in temperature could affect the rate of osmosis occurring, due to the water molecules moving faster, and a higher rate of osmosis in one of the tubes could result in a larger increase/decrease in mass)
Potato chips taken from,(because different potatoes may have different sucrose concentrations, so the osmosis occurring would be different in that a potato with a high sucrose concentration would gain more mass in the lower concentrations and loose less in the higher concentrations than a potato with a low sucrose concentration, creating different results)
Volume of solution,(Because if a chip were put in a smaller volume of solution, then the number of water molecules would be smaller and less osmosis could take place)
Light levels falling on experiment,(Increased light levels falling on the experiment could increase temperature, resulting in the same problems as straightforward temperature increase)
Type of potato (King Edward),(differences in potato varieties mean one type could have a higher/lower sucrose concentration, resulting in different results to other varieties)
Size of chips.(difference in chip size would change the results by giving the appearance of a larger change in mass than is true)
Surface area of chip.( larger surface area would result in faster osmosis, so a larger change in mass over the time period)
Equipment:
6 test tubes (to put the solutions and chips in)
1 10mm borer (to take pieces of potato)
1 ruler (to measure length of chips)
1 top pan balance (to measure the mass of the potato chips before and after experiment)
1 sharp scalpel ( to cut chips to size)
1 large potato (to take chips from)
6 sugar solutions of varying concentrations; 0%, 10%, 20%, 30%, 40% and 50% (to place potato chips in to find concentration)
1 stop clock that will time 1 hour (to keep amount of time in solution the same for each chip)
1 test tube rack (to hold the test tubes during the experiment)
6 soft tissues of the same make (to remove excess solution from the potato chips before their mass is measured)
6 beakers (for mixing the different solutions in)
6 30ml measuring cylinders ( to measure amount of solution each chip is placed in)
1 pair of tongs (to remove chips from solutions)
Method: 1.Prepare a range of sugar solutions of varying concentrations; 0%, 10%, 20%, 30%, 40% and 50% in separate beakers to prevent contamination.
2. Take 6 sections of potato using the 10mm borer, remove skin
3. Carefully cut each section to 50mm in length using the scalpel & ruler
4. Measure mass of each chip with top pan balance to ensure each is almost the same. Any major differences mean the chip must be discarded and a fresh one made.
5. Record your mass readings for future use in a results table.
6. Take six clean test tubes and place them in a test tube rack. Label each according to which solution it is to contain.
7. Place 25ml of relevant solution in each test tube.
8. Place a potato chip in each tube at the exact same time and start the stop clock
9. Leave chips for one hour
10. Carefully remove chips with tongs, remove excess moisture with soft tissues and instantly measure the mass of each using the top pan balance. Record data.
11. Repeat experiment twice to check your findings
12. Record your findings in a results table like the one below.
13. Draw a graph from your results for either length or mass (mass included in this investigation) including a line of best fit.
Results
Conclusion:
From the graph it can be seen that the prediction was almost correct, and that the investigation was successful in that results obtained backed up the prediction’s statement that mass will decrease in strong solutions (above 10% concentration) and increase in weak solutions (below and including 10% concentration). The pattern on the graph has been shown with a line of best fit. From this the trend towards a larger decrease in mass as the solution concentration increases can be seen clearly. This trend coincides with my previous knowledge mentioned in the prediction and introduction, providing proof that osmosis occurred as was expected. From the results obtained, the aim can be met approximately. Using the results for 10% sucrose concentration and 20% sucrose concentration, the sucrose concentration within the potato used can be estimated at 12%. Further tests would be needed to determine exactly the concentration within the potato. By looking at the masses of the potato chips before the experiment it seems that the experiment was carried out accurately, and all measurements were made precisely. No truly anomalous results occurred, and any that seem odd are probably due to natural variations of concentration within the potato’s individual cells. Overall the experiment was carried out well and the results would be very similar if it was repeated.
Evaluation:
The experiment could have been improved by repeating it more than twice to get a better range of readings so a more accurate average could be obtained. Also, the use of larger pieces of potato would of resulted in larger changes in mass and length, so more accurate readings could be obtained. Further testing could be done to determine the exact sucrose concentration within the potato, using a range of more specific solutions, possibly 1% increments between 10 and 20%. Also, osmosis could be studied further by investigating if placing the used potato in an opposite solution can reverse osmosis. To explain more clearly, a preliminary second method has been provided.
1. Prepare 2 sucrose solutions of 0% and 50%
2. Take a section of potato using a 10mm borer and remove any skin.
3. Carefully cut this section to 100mm in length using the scalpel & ruler
4. Measure the mass of this chip with a top pan balance. Record its mass.
5. Take 2 test tubes and label them according to which solution the will contain.
6. Place the test tubes in a test tube rack and carefully measure out 25ml of each solution and pour it into the relevant tube.
7. Place the potato chip in the tube containing the 50% solution. Start a stop clock as the chip enters the tube.
8. Leave the chip for one hour.
9. Carefully remove the chip with tongs, remove any excess moisture with a soft tissue and measure the mass immediately with the top pan balance. Quickly record the result.
10. Place the chip into the test tube containing the 0% solution as quickly as possible to prevent evaporation and start the stop clock.
11. Leave the chip for 1 hour.
12. Carefully remove the chip with the tongs, remove any excess moisture with a soft tissue and measure the mass with the top pan balance. Record the result.
13. Repeat experiment 3 times to check your findings.
This preliminary experiment would determine whether or not osmosis is reversible and a full investigation into this matter could then be performed.
Other than those things, not much else could be changed, as the results were very reliable due to the extensive precautions taken to make it a fair test. In the future yet more experiments could be performed to learn more about osmosis, such as seeing how time affects osmosis or how surface area exposed to solution affects rate of osmosis. Also, different vegetables could be used to examine variations in sucrose concentration in different species.
