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The aim of this experiment is to find out how the mass (in grams) of potato tissue changes when placed in varying concentrations of Sucrose.
Cutting tile – to cut the potato on
Knife – to cut the potato
Graduated pipette – to fill the bottles
25cm Measuring cylinder – to measure solutions
Distilled water – to act as a control
The following Sucrose solutions 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 molar concentrations – to submerge potato tubes into.
Potatoes – to cut up and test
Tissue paper or cloth – to dry the excess surface water off prior to weighing the potato chips.
Electronic Balance – to weigh the potato chips
Cork borer – to cut out 33 identical potato cylinders
33 30ml bottles with lids – to hold potato chips and glucose solutions
Prior to doing the actual experiment, I performed a few tests on a small number of potato chips to find out how long the chips should be left in the Sucrose solutions for. I found that after being left in distilled water for 10 minutes there had been no mass change, so I left the next one in for an hour and after weighing found that there head been little change.
So I left a final one in for 24 hours and found the result of the weighing to be most satisfactory. The chip had dramatically increased in mass.
Osmosis is the net movement of water molecules across a partially permeable membrane from an area of high concentration to an area of low concentration.
Plant cells always have a strong cell wall surrounding them.
When they take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant cells become “turgid” when they are put in dilute solutions. Turgid means swollen and hard. The pressure inside the cell rises, eventually the internal pressure of the cell is so high that no more water can enter the cell. This liquid or hydrostatic pressure works against osmosis. Turgidity is very important to plants because this is what make the green parts of the plant “stand up” into the sunlight.
When plant cells are placed in concentrated sugar solutions they lose water by osmosis and they become “flaccid”; this is the exact opposite of “turgid”.
When plant cells are placed in a solution which has exactly the same osmotic strength as the cells they are in a state between turgidity and flaccidity. We call this incipient plasmolysis. “Incipient” means “about to be”. When we forget to water potted plants you see their leaves droop. Although their cells are not plasmolsysed, they are not turgid and so they do not hold the leaves up into the sunlight.
Fair testing should play a big part in this experiment. If this experiment isn’t a fair test, we will be obtaining inconclusive and potentially unrepresentative 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 donï¿½t 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 isnï¿½t 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.
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 itï¿½s not handled properly. And we will also be careful that the solutions donï¿½t 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 werenï¿½t any bigger matters to be cautious of.
In this experiment, I believe that I have collected enough data to support my hypothesis. This investigation was, I think, successful. Successful meaning my results collaborated my predictions.
The potato cells, working to stay alive, took in, or gave out the water depending on the concentration of the tissue, and the concentration of the solution it is surrounded in.
The results were fine and by looking at the weights measured before the experiment, you can see that there is no reading which seems to be out of the line. As the weights before the experiment range between 5.62g and 5.87g, this tells us that the potato pieces were cut well, and I believe accurate enough. There were, I believe, no anomalous results after the experiment as the weights were very similar in their own category. And this tells us that my experiment was successful.
The graphs and the results show that:
v Osmosis actually took place in the experiment.
v As the molars increased, the percentage of the weight difference decreased.
There doesnï¿½t seem to be any results, which undermine my predictions, and our group didnï¿½t find any anomalous results, which means we didnï¿½t have to repeat any of our experiments more than three times.
Having the results which backs up my hypothesis, proves that this investigation was fully accomplished, and was an achievement.
Solution Weight Weight Weight + or – Percentage change
Before(g) After(g) (g) (%)
water 5.84 5.87 0.03 0.55
0.2 5.84 5.84 0.00 0.07
0.4 5.76 5.61 -0.15 -3.15
0.6 5.87 5.58 -0.29 -5.89
0.8 5.76 5.41 -0.35 -7.35
1 5.77 5.38 -0.39 -8.18
In the table above, the percentage shows a steady decrease, telling us that the percentage of the difference decreases as the water concentration decreases.
This experiment helped me find out that osmosis occurs between 2 liquid substances with a partially impermeable membrane, and that higher the water concentration is, the larger increase in grams. This means that the percentage will also be higher, increasing with the gram.
We followed the plan correctly, I believe we gained accurate and sufficient enough results to conclude the experiment, and to prove our hypothesis.
My final results were very reliable, due to the precautions I took to make this a fair test.
To make this experiment better, I believe that we could have done one test at a time, so that we can reduce the time difference, when we have to move the potato from the test tube to the balance. Between this, we have to dry the potatoes just enough, and then put it on the balance. When we are doing this for one set, writing down the results at the same time, while the other 5 sets are on the tissue paper, the water outside the potato tissue is going to vary for all. Therefore, we would be able to concentrate more on one of the sets, instead of trying to finish all of them as quickly as we can.
We also could have got more people to do the experiment with us, so that we can organize the tasks, and we would be able to divide the tasks.
Using more types of molar sucrose solutions would have helped us obtain better results, and more accurate results, so that we can make sure the results are totally correct.
Experimenting with one set for a longer period of time, for each set, would lead us to better results, because the osmosis action would reach its maximum capability, and therefore tell us how much water could be transferred for each solution.
Repeating the same tasks many other times wouldnï¿½t have been very useful, since we had already done the result 3 times, and ALL the results were reliable.
Even though we didnï¿½t use these experimental plans, we still got results which were correct, according to my hypothesis, and backed up my predictions.
But overall, given the apparatus that we got to carry out the test, I think this experiment turned out to be very successful, and Iï¿½m very please with my results.
?????????”I predict that the potato chip will decrease more in mass in the stronger glucose solution”, has proven to be right. The reason for this is because that osmosis will make water molecules move from a high water concentration to a low water concentration. All my graphs show that stronger the glucose concentration the lighter the chip is in mass (grams). The pattern which Iï¿½ve noticed is that all my graphs generally form a slope when joining up all the points. Also I have learnt that the water from the potato chip can only be absorbed a certain amount then it stays the same mass like in trial 1.
In trial 1 the graph looks totally fine. It looks that 60% glucose concentration is its peak decrease out of all the potatoes. That may of happened because that certain chip may have more water to release then the others, or 60% is the maximum amount that the potato tube can work best to decrease in mass.
In trial 2 the last 2 results look weird. I think the reason for this is because my method was not good enough. When filling each of the test tubes with glucose, I did not use a measuring cylinder to measure the required amount. I just poured until the glucose solution covered half of the test tube. That may look same in all the test tubes but I might of added extra or less to it.
To improve my method I would definitely use a measuring cylinder next time in order to receive a high standard of results.
I would also improve the range of glucose concentration. Instead of it going in 20ï¿½s, I would prefer to have the glucose concentration in 10ï¿½s, up to 100. This way you have a vast variety of readings to look at.
When I do another experiment I am going to plan my method in advance in order to be more organised, that way less inaccurate readings will happen and it will make everything run smoothly and efficiently.
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