Fair Test
Fair testing should play a big part in this experiment. If this experiment isn´t a fair test, we will be obtaining the wrong results, which could lead us to the wrong conclusions. First of all, and most importantly, we will have to get the measurements and the weights of the solutions and the potatoes as exact, and as accurate as possible. We will try and get the measurements of the potatoes as accurate as possible for every single potato, evenly cutting the potato pieces, and making a record of the length to the nearest millimetre. And we will be using a very sensitive balance so that we can get the best readings possible. But I believe one of the most important step in the fair testing is to make sure that the potato is fully covered by the solution. This is because the potato should fully submerge, by having total contact with the solution. When using the balance, we will make sure that the balance is reading zero with the small foam bowl, before we put the 3 potatoes on it. This is so that we don´t get a false reading, with the weight of our potato with the reading it had before. And after the experiment, we will measure the 3 potatoes that should be dried as possible, and weigh it the same way, taking the reading to the nearest 2 decimal places.
And we will also be reading the measurements of the measuring cylinder by reading the bottom of the meniscus. Carrying out the experiment in a constant temperature for the three hours of experiment is important. And to avoid temperature change, which might affect our 3 different sets of results, we will take the temperature of the solution into account. Another important factor of a fair test is to start and stop the clock as quickly as possible. This meaning that we should start the clock as soon as the potato is put inside the test tube, and stop the clock as soon as 20 minutes have passed. Stopping the clock, taking them out and measuring it all in less than a minute us quite impossible because we lack the number of balances. And there are obviously too many sets to go through at such a fast time. Therefore, we will try our best to weigh the potatoes as quickly and as safely as we can. Getting and experimenting with the exact measurements of molars and water is vital to this task. If the volume of one solution in a test tube is higher or lower than another, will affect the pattern of results later on. We will also make sure that the potato is fully covered by the 6 different kinds of solutions. This is because, is the potato isn´t covered up by the solutions, the effect of osmosis might not occur to the fullest. Small things such as a dirty test tube, and a slightly cracked measuring cylinder could still affect the results, and therefore we will take these into account as well.
Variables
The several different factors that affect the rate of osmosis:
Potato tissue: The number of cells that make up the tissue also help in the taking in or out of the water from or to the semi-permeable membrane increasing or decreasing the process.
Potato mass: The more the weight of the potato the more likely for the tissue to have more cells passively working on the process.
Water volume: The more or less water means a dilute or concentrated solution which increases or decreases the diffusion of water.
Sucrose solution : The molarity of sucrose in the solution means the solution is either high or low water concentrated so controlling the amount of water diffising in or out of the cell.
- These are classified under three types of variables.
Fixed variables : these are factors I will keep the same in the experiment for a fair test:
a) Length of potato
b) Volume of water
Dependent variables: the factors that will change as investigation is rooted in the results:
- Weight of potato
Independent variables: what I will change into the factors affecting the rate of reaction:
a) Molarity of sucrose
Preliminary work
In the investigation we did a preliminary pilot study to see how osmosis happens and where water diffuses from and to by the use of visking tubing.
Apparatus
2 beakers, balance
2 visking tubes
sugar solution
water solution
Pilot Study
Diagram
Analysis of pilot study
From the results of the pilot Study I realised that the water visking tube weighs less after being put in the sugar solution for 20minutes but the sugar visking tube weighs more after being put in the water solution for 20minutes . This proved that osmosis is diffusion of water from a region of high to low concentration as the water from the tube to the solution or from the solution to the tube depending on which is high or low water concentrated.
Potato Cylinders
Apparatus
· Stop Clock - to time our experiment
· Cutting tile - to cut the potato on
· Knife - to cut the potato
· 25cm Measuring cylinder - to measure the solutions
· Distilled water - part of the experiment
· sucrose - part of the experiment
· Potatoes - part of the experiment
· Tissue paper - to dry the potatoes after the osmosis takes place
· Balance - to weigh the potatoes
· Cork borer - to cut out potato cylinders
Safety
Safety is an important aspect in every experiment, even if the experiment seems to be very harmless. And that is why we take this into consideration, no matter what. We will be using a very sharp knife, which could injure someone if it´s not handled properly. So we had one person cutting the cylinders to reduce the probability of people getting injured. And we will also be careful that the solutions don´t get into our bodies internally, just in case, because we are not fully aware of the damage it could do to us. But other than that, there weren´t any bigger matters to be cautious of.
Method
I believe this task is very simple and should be very easy to carry out the experiment. The investigation is very straightforward.
There won´t be any control for this experiment, because the weight would vary depending on the potato pieces. And therefore, it might affect the results, which we are going to take in after the experiment.
First I will have to get the pieces of potatoes ready. I will push the cork borer through the potato, cutting it into long cylinders with a diameter of 6mm. And then I will cut the potatoes into cylinders of 40mm, and weigh 6 sets of 3 potato cylinders. I will have 6 sets because we will have to test the potatoes in 6 different types of solutions; 0.2, 0.4, 0.6, 0.8, 1.0 molar solutions of sucrose, and distilled water.
I will weigh each set and have them ready for us to put into the test tube.
Then we will put the 6 sets of 3 potatoes in the 6 test tube at the same time and start the clock running for 10 minutes.
After 10 minutes, we will take all of the potatoes out of the test tube, so that the actual osmosis action stops, and we will put the potatoes onto one piece of dry towel, in their own groups. We will dry them with the tissue paper, in sets of 3, and weigh and measure the potatoes taking in the average reading of the 3 pieces.
We will repeat the experiment three times so that we can make sure that all our results are similar, and so that we will be able to take the average of the 3 experiments. This makes sure that we get accurate results. Repeating the experiments are important, because we will be able to receive valid results, and look for any anomalous results. Not to mention that we will take the fair testing into account.
Obtaining evidence
After the experiment, I had to dry the potatoes first, so that the water outside the tissue of the potatoes won´t alter the weight of what it is supposed to be. I quickly took all of them out, and put them onto a piece of tissue paper, into their own groups.
When obtaining my results, I reset the balance, so that it would read zero with the small foam bowl on top of it. This was because, if I had weighed the potatoes with the bowl, then I would have to take the weight of the bowl away from that result.
Table of results
In the table below, it shows the 'solution´ column, which are the 6 different types of solutions. The 'number of test´ column, which shows the number of tests that took place, and the average of the three tests. The weight before and after the experiment represents the 3 sets of results and the average taken out of the three. The increase/decrease of the weight is calculated by taking the weight after, minus the weight before. The percentage increase/decrease of the weight of the potato is calculated by taking the weight increase/decrease divided by the original weight multiplied by a hundred. This should help us lead to a more accurate result, and the average percentage will be used to present the graph.
Table
Analysis of table
The table above shows that the more sucroce in the solution the less the weight of potato after bieng put in the solution. As osmosis Is diffusion of water from a high to a low concentrated region the concentrated solution will have a low water concentration so water will diffuse into it making the potato swell but the dilute solution will be high in water concentration so water will diffuse from the potato to the solution making the potato shrink. From the table we obtained decreases or increases in percentage and the potatos that had decreased or increased were classified under the three variation contents in solutions which are:
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Hypotonic: The solution with the lower concentration of solutes e.g 0.0M
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Hypertonic: The solution with the higher concentration of solutes e.g 0.4M, 0.6M, 0.8M
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Isotonic: The solutions being compared have equal concentration of solutes e.g 0.2M
From the variation contents in solutions the cells changed and I classified the changes under the three types of plant cells:
