Determining the Solute Concentration of a Potato, Gcse Ocr 21st Century Biology Coursework

Determining the Solute Concentration of a Potato
Aim: In this investigation I am going to work out the sugar concentration of a potato. I aim to find this out by putting potato cores into various concentrations, measuring the mass before and after. Due to osmosis the potato cores will change in mass to make the concentrations at an isotonic level, helping us to work out the mass of the potato. I predict that potato in the weaker solutions will gain mass, because some water will be absorbed by the potato to make the concentrations isotonic. Similarly, I think the potato in the stronger solutions will lose mass as they will have to lose water to dilute the stronger solution.
Osmosis: Osmosis is the diffusion of water across a partially permeable membrane. This happens when an area of high concentration and an area of low concentration are separated by a partially permeable membrane. Water disperses through the membrane to reach equilibrium and perfect balance between water and glucose. When the ratio between water and glucose is equal on both sides it is isotonic.

Preliminary Experiment: Before my main investigation I aim to do a preliminary investigation to ensure I get the most accurate results. In the preliminary investigation I will be testing core sizes of the potato, the range of concentration of solutions and the duration of time that the potato is in the solution to establish which ones I will be using for the main investigation. Equipment for the Preliminary Experiment: * Potato * Sharp scalpel to precisely cut the potato cores * Potato corers in sizes 1, 3 and 5 so we can determine the best one to use in our main experiment * Clean ceramic tile to core and cut the potato on without compromising the experiment * Test tubes to put the potato pieces and the solutions in * 3 test tube racks to put the test tubes in. Each mini-experiment can then be kept separate to reduce the chance of mixing the test tubes up * Measuring cylinder to accurately measure the sucrose solution * Sucrose solutions in a range of concentrations (1.25%, 5% and 20%) in order to determine results * Tweezers to handle the potato cores and to avoid contamination for hands * Balance (accurate to one 10th of a gram) to weigh the potato pieces to establish precise results * Stopwatch, to time each experiment to ensure a fair and accurate test and set of results * Ruler in order to measure the cores so they are all the same size. This ensures a fair test * Pencil to write on the test tubes and prevent a mix up * Paper towels to dry off excess water from the potato cores that could give an inaccurate mass
Method
1. Set up the equipment and label each test tube with which experiment it is used for. 2. Core the potato’s and accurately cut the cores so that they are all 3cm long. For the core size test 3 size 1 cores, 3 size 3 cores and 3 size 5 cores will be needed. Then cut a further 6 size 3 cores for the time experiment and the experiment testing the range of solutions. 3. Weigh each core on a balance accurate to 1 10th of a gram and record the mass. 4. Start with the experiment testing time (Experiment 1). Place one size 3 core into a test tube labelled 45 minutes. Then measure out precisely 10cm³ of solution with a 5% concentration with a measuring cylinder and pour into the test tube. Start the stopwatch (timed for 45 minutes) 5. While waiting for the 30 minute time test of experiment 1, experiment 2 (core size) can be started. Place 9 cores of the 3 different sizes into the appropriate test tubes. Then add 10cm³ of 5% concentration solution into each of the size 1cores test tubes and begin timing for 30 mins. (By staggering the experiments you have more time to weigh and record the mass at the end of the allotted time.) 6. After 2 minutes repeat this for the size 3 cores and after a further 2 minutes the size 5 cores. (By staggering the experiments you have more time to weigh and record the mass at the end of the allotted time.) 7. After 15 mins the next stage of experiment one (time) can begin. Add the next size 3 core to the test tube labelled 30mins. Then add 10cm³ of 5% concentration solution and time for 30mins. 8. Meanwhile, experiment 3 can be started. Experiment 3 tests the range of concentrations. Place 3 cores into 3 test tubes and measure using a measuring cylinder 10cm³ of 1.25% concentration solution. In another cylinder measure 10cm³ of 5% concentration solution and in another 10cm³ of 20% concentration solution. 9. In the test tube accordingly labelled pour the 1.25% solution and time for 30 minutes. In two minutes add the 5% solution to another test tube and after a further two minutes add the 20% solution to a third test tube. 10. After 15 mins the next stage of experiment one (time) can begin. Add the next size 3 core to the test tube labelled 15mins. Then add 10cm³ of 5% concentration solution and time for 15mins. 11. After the 30 minutes is up for experiment 2 (core size) remove the size one cores from the test tubes and place them on paper towels. Gently roll the cores to remove any excess moisture that could compromise the experiment. Using the same balance as before weigh the cores and record the results. After 2 minutes repeat for the size 3 cores and again after another 2 minutes for the size 5 cores. 12. After the 30 minutes for experiment 3 (range of solutions) is up remove the core from the 1.25% solution using tweezers and gently roll on the paper towels. Weigh and record. After 2 minutes repeat for the 5% solution and after a further 2 minutes repeat for the 20% solution. 13. When the allotted time (45 minutes, 30 minutes and 15 minutes) is over for the time test remove the cores from the test tubes using tweezers and dry off gently using paper towels. Weigh and record the mass.
Results: Core Size Test | Small Corer (size 1) | Medium Corer (3) | Large Corer (5) | Before Mass | 0.3g 0.3g 0.3g | 0.9g 0.9g 1g | 1.6g 1.6g 1.6g | After Mass | 0.3g 0.3g 0.3g | 0.9g 0.9g 1g | 1.7g 1.6g 1.6g | Change in Mass | 0g 0g 0g | 0g 0g 0g | 1g 0g 0g |
Testing the Range of Concentrations | 1.25% | 5% | 20% | Before Mass | 1g | 1g | 1g | After Mass | 1g | 1.1g | 1.g | Change in Mass | 0g | 0.1g | 0g |

Testing Time | 15 mins | 30 mins | 45 mins | Before Mass | 1g | 0.9g | 1g | After Mass | 1.1g | 1g | 1.1g | Change in Mass | 0.1g | 0.1g | 0.1g |

Preliminary Results Analysis
My preliminary experiment was to help me finalise my method and equipment for the main investigation. Using the results I have decided to change many things before my main experiment.
In my preliminary experiment I used a balance that was accurate to 1 decimal place. In my main investigation I will try to use one that is accurate to 2 decimal places for more precise results.
I have decided to have my potato cores in the solutions for 45 minutes. This gives more time for osmosis to occur, and although in my preliminary experiment the change in mass was the same for all of the time periods, with a more accurate balance this might be different.
I have also decided to use more solutions in my main investigation, for example 2.5% and 10% as well as the ones I used in the preliminary experiment. This will give me a broader range of results and a more accurate line of best fit on my graph. From this I will be able to determine a more reliable line of best fit.
The size 5 corer was the only one to give a change in mass, so I have decided to use this one in my main investigation.
I will also need to repeat each concentration at least three times so I can easily identify any outliers and get a reliable mean.
To improve the reliability of my results I will also I make sure that I have washed each measuring cylinder after using it to prevent contamination between each concentration solution, or use different measuring cylinders for each concentration.

Finalised Equipment List: * Potato. For the main experiment use one big potato so all the cores come from the same one. This makes the experiment more accurate. * Sharp scalpel to precisely cut the potato cores. * Size 5 potato corer so the potato pieces are all the same width. * Clean ceramic tile to core and cut the potato on without compromising the experiment. * 18 test tubes so there are 3 for each concentration of solution. * 3 test tube racks to put the test tubes in. * 5 measuring cylinders to measure the sucrose solutions (one for each concentration to prevent contamination) * Sucrose solutions in a range of concentrations (1.25%, 2.5%, 5%, 10%, 20% and 30%) in order to determine results. * Tweezers to handle the potato cores and to avoid contamination from hands * Balance which is accurate to 100th of a gram. This is to establish more accurate results. * Stopwatch, to time the experiment to ensure a fair and accurate test and set of results. * Ruler in order to measure the cores so they are all the same size. This ensures a fair test. * Pencil to write on the test tubes and prevent a mix up. * Paper towels to dry off excess water from the potato cores that could give an inaccurate mass.

Method for Main Investigation:
1. Set up equipment. Make sure to label each of the 18 test tubes with the concentration they will be holding
2. Using a size 5 corer, core the potato and cut to exactly 3cm using a sharp, clean scalpel
3. Weigh the potato cores on the balance and record the mass of each.
4. Measure out 10cm³ of 1.25% sucrose solution 3 times. After the solution has been poured into 3 test tubes start the stop watch for 45 minutes. By repeating each concentration 3 times we can identify any anomalies and calculate an average. Repeat this for all the other concentrations of solution, leaving 2 minutes between each. This two minute interval will leave time for weighing at the end of the experiment.
5. Once the 45 minutes is up, remove the potato cores from the 1.25% concentration, gently dry them will paper towels and weigh them using an accurate balance. Do the same for the other potato cores, remembering that you left a two minute interval between each, and remembering the order in which the solutions were added.

Safety Precautions: When doing the main investigation I made sure to follow the following safety precautions: * I wore safety goggles at all times * I tied my hair back and took off any jewellery * I was extremely careful when using the scalpel and made sure I put the cap on when it wasn’t in use * I made sure there were no bags about and all chairs were tucked in, as these could be tripping hazards * I handled the glass test tubes careful so I didn’t drop and smash them

Control Variables: I will make sure I use the same size corer and cut each potato core to the same length. If the size varies, the experiment will be compromised. We cannot be sure that the change in mass that will occur will be because of the different concentrations of solution, or because of the size of the cores. The results would be unreliable. I will ensure that I use the same volume of sucrose solution for each potato core, as varying the volume could again compromise the experiment. I will make sure I use the same potato throughout as different potato’s could have different water and solute contents. A major variation in the water and solute contents between potato’s will create different osmotic effects and this could affect our results. I will also ensure that the potato cores are submerged in the solutions for an equal amount of time. More time could allow for more osmosis to take place and the test wouldn’t be fair. It is also important to control the temperature. Osmosis occurs more rapidly at higher temperatures as the particles move more rapidly. If the temperature doesn’t remain constant throughout the experiment, it could produce unreliable results. The independent variable is the concentration of solution. The dependant variable is the change in mass of the potato cores. Results: Dependent Variable, mass of the potato core | Indepen-dent variable, conc. of solution. | Before Mass (g) | After Mass (g) | Change in Mass (g) | % Change in Mass(change÷ before mass x 100) | Mean % Change | 1.25% | 1.7 | 1.75 | 1.61 | 1.78 | 1.79 | 1.67 | 0.08 | 0.04 | 0.06 | 4.71 | 2.86 | 3.73 | 3.77 | 2.5% | 1.74 | 1.66 | 1.61 | 1.82 | 1.71 | 1.67 | 0.08 | 0.05 | 0.06 | 4.59 | 3.01 | 3.45 | 3.23 | 5% | 1.65 | 1.65 | 1.62 | 1.69 | 1.68 | 1.65 | 0.04 | 0.03 | 0.03 | 2.42 | 1.82 | 1.85 | 2.03 | 10% | 1.62 | 1.68 | 1.66 | 1.6 | 1.61 | 1.62 | -0.02 | -0.07 | -0.04 | -1.23 | -4.17 | -2.41 | -1.82 | 20% | 1.57 | 1.62 | 1.62 | 1.37 | 1.42 | 1.43 | -0.2 | -0.2 | -0.19 | -12.74 | -12.35 | -11.73 | -12.27 | 30% | 1.66 | 1.77 | 1.62 | 1.28 | 1.33 | 1.22 | -0.38 | -0.43 | -0.4 | -22.89 | -24.29 | -24.7 | -23.96 | Anomalies: The results in bold are significantly different to the other results so I have marked these as outliers. They are not included in the mean or the graph.