Designing an Osmotic Potential Experiment with Potatoes
Designing an Experiment on Osmotic Potential
Osmosis is used throughout the kitchen in various countries. In France, aubergines and cucumbers are often soaked in salt to create a nicer texture, however chefs lack understanding of why this happens, as they would have forgotten about it after they finished school, they only know that it happens. Therefore, this experiment is designed to explain to the millions of chefs around the world why the water is “sucked” out of a vegetable when it is dipped into a salt or sugar solutions. I believe that having knowledge over the reason for something can open up new ways of thinking; this is why I think it is so important to explain the reason behind this phenomenon.
Famous chefs are also known to be under time pressure; for example, every cooking show on TV includes some sort of time pressure scenario, weather it is a ticking clock or waiting customers. For this reason, I would like to help these chefs save time by designing an experiment to determine the different lengths of time it takes a vegetable to be completely rigid or flaccid, this would help the chefs create the best texture in the shortest amount of time.
Therefore, I am setting up an experiment to test the minimum time required for a sucrose solution to create a desired result of either a flaccid vegetable or a rigid vegetable. I will also be setting up an experiment to show the mass change of the vegetables in each of the solution, and trying to find the osmotic potential of the vegetable.
According to particle theory, water molecules are in constant motion. As they move, they hit the membrane and create a pressure against the membrane called the water potential. Solutions with a low water potential have a high solute (osmotic) potential. Therefore, solutions with a high water potential have a low solute (osmotic) potential.
The time it takes for a vegetable cell to reach a turgid or plasmolyzed state would not be more than one hour as this is the standard experiment time in the UK and around the world. Therefore, my hypothesis will be that it will not take any longer than one hour for the vegetable to reach a turgid or plasmolyzed state. For osmosis to happen as quickly as possible, the gradient should be as steep as possible; therefore I am expecting the saturated solution and the pure water to change the water-level of the vegetable fastest.
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Materials and Apparatus
For this experiment I will need little apparatus, the apparatus I will need will be the following:
- Seven jars, preferably one that can hold more than 0.5l of water.
- Potato, I will use one or more potatoes.
- Sugar, sugar will be used as the solute.
- Spoon, to stir the solution.
- Clock, to monitor the time.
- Still water, to be the solvent.
- Scale, to measure the mass of the potato and sucrose.
- Knife, to cut the potato.
- Measuring cylinder.
My independent variable will be the different solutions I will use; the solutions will include a range from pure water to a saturated sugar solution. This will be my independent variable as it will be the one I plot on the x-axis. This is an important variable because in both home and professional kitchens, people need to know what amount of solution is enough for their purpose. This variable will be manipulated by using different amounts of sugar in the solutions, the sugar will first be weighed out, then I will add tap water into the solution, upon reaching the desired volume I will stop. The sugar must be weighed out first because if I fill the jar with 1l of water and then add another 342.3 grams of sucrose the total volume will exceed 1l.
I will have 7 different solutions of sucrose, they will be: 0 molar solution (pure water), 0.2 molar solution, 0.4 molar solution, 0.6 molar solution, 0.8 molar solution, 1 molar solution and finally a saturated solution.
Another independent variable will be time, this is to see at what rate each solution will reach the maximum or minimum mass. This, as explained before, is crucially important as it will be a huge resource for chefs with time-pressure. This particular independent variable cannot be manipulated by me, I will just have to take a reading every 10-15 minutes.
My dependent variable will be percentage change in mass. This will be for both my independent variables. The dependent variable is what I will be measuring, I will be measuring the change in mass, and then convert them to the percentage change. I will convert the mass into percentage change as this will give me a better reading as my slices of vegetable might not be the same mass. However, I will try to cut my slices the same size so this is only added as an insurance. I will measure the mass of each individual vegetable slice. Then I will find the mean and mode of the slices. This will help me determine what mass would be the closest representative of the actual mass.
Another dependant variable will be time, time on the y-axis and my different solutions on the x-axis will become a very nice graph as it will display how long time each potato will take to reach a turgid or flaccid state.
During this experiment there are many control variables that I need to take into consideration in order for my method to be valid. Therefore the control variables need to be carefully considered and revised.
- The mass of my vegetable slices in the beginning of the experiment must be the same. I will make sure that I weight the vegetable slices prior to conducting the experiment.
- The molarity of the solutions must be measured accurately. To ensure this, I will look on the periodic table and online for the molar mass then I will use a scale that measures to the closest 0.1 grams to determine that my mass is correct.
- The number of stirs in the sugar solutions need to be the same. I will stir the solutions each five times with the same sized spoon.
- The slices of vegetable should come from the same part of the vegetable. I will make sure that the slices of vegetable are cut from the same portion of the potato, I will also make sure that there is no skin left on my potato.
- The slices of vegetable must have the same mass, volume, surface area and shape. I will measure the dimensions of the vegetable slices and calculate the volume and surface area of them. I will make sure that they are as close to each other as possible.
- When measuring the mass, the vegetable slices must be dried in the same way. I will tap each side of the vegetable on the tissue for a duration of approximately 0.3 seconds.
- Each slice of vegetable should be out of the water the exact same time when measuring the mass. I will ensure that this is done by taking no longer than 15 seconds to dry the vegetable and take the measurements.
- The slices of vegetable must be dropped into the solutions with a time interval of 1 minute. This will be conducted as I will closely monitor the time. I will drop the potatoes into the solutions at different time as this gives me time to calculate the mass when I take my measurements.
- The temperature of the solutions must be the same. Tap water will be the desired choice for this experiment as it is the purest water that I can get hold of. The tap water also has a stable temperature if I run it cold first. Therefore I will use tap water for this experiment.
- The volume of each solution must be the same. The volume will be 0.5l, I will measure this out with the jars that I am using.
- The mass gained or lost by the solution should equal the mass lost or gained by the vegetable. This I will test by weighing the mass loss of the vegetable at the end of the test, I will also measure the volume change in the jar. These two numbers should be identical.
- All experiments must be conducted in a temperature-regulated environment. I will control this by making sure I conduct the experiment indoors in a ~200C environment.
I feel that the control variables above will provide a fair environment for a scientific experiment.
I will first cut the vegetable into equal sized slices, after I have cut them I will measure the mass of the slices, this is to ensure that the mass of the slices are as close as possible to each other. Then I will proceed to creating the different molar solutions. To do this, I will first measure the mass of sucrose I will use, then I will place the sucrose into a jar and fill the jar with water until the volume reaches 0.5l. After this has been complete, I will drop the different slices of vegetable into the solutions at one-minute intervals, this is to give me time to take measurements afterwards. After this is complete, I will take the slices gently out of the solution to measure them. The slices of vegetable will be dried by tapping each of the sides once on a paper towel. After taking the mass I will quickly insert the slices of vegetable back into the solution, the slices will be taken out of the solutions at one-minute intervals, this will make sure that the slices stay in the water for the same amount of time before being measured. I will collect data for as long as I can, however I am expecting the preparation work to take no longer than 45 minutes, therefore I should get at least seven sets of data.
Sufficient and relevant data will be collected with a scale. After knowing that the scales I will be provided with only measure to the closet gram I have decided to bring my own scale, the scale measures to the closest 0.1 grams, this will be enough for my use. I will make sure that the measurements are taken up to the highest standard as my results will be less valid if I do not take my results accurately.
The safety of this experiment also needs to be taken into consideration. To avoid injuries or potential death I will be careful with the knives I use and put them away adequately once I have completed my task involving them. I will also handle the glass jars carefully as this is also a safety issue.