The Impact of Sucrose Concentration on Osmosis in Potatoes

Aim

My main aim in this experiment is to find out if osmosis occurs in a potato, and how it affect the potato in different molar solutions of sucrose and water.

Apparatus

• 6 petri dishes û for all of the six solutions
• Marker pen û to label the petri dish, just in case of a mix up
• Beakers û to pour the solutions into the petri dish
• Stop Clock û to time our experiment
• Cutting tile û to cut the potato on
• Knife û to cut the potato
• 25cm Measuring cylinder û to measure the solutions
• Distilled water û part of the experiment
• 2, 0.4, 0.6, 0.8, 1.0 molar solutions of sucrose û part of the experiment
• Potatoes û part of the experiment
• Tissue paper û to dry the potatoes after the osmosis takes place
• Balance û to weigh the potatoes
• Cork borer û to cut out potato cylinders

Planning

Before actually planning the experiment, I will do some research to find out about osmosis, and matters related to it, so that I can make predictions. And figure out a way to make this investigation fair and safe.

Planning ahead would help me find out how to do what, when, which should lead me to good results at the end of the experiment.

Hypothesis

Osmosis is the passage of water molecules from a weaker solution into a stronger solution, through a partially permeable membrane. In this case, the tiny holes in the membrane of the potatoes will allow the water molecules to pass through in and out of the solution and the potato, depending on the concentration gradient of the two substances. So in this case, when the water concentration is lower in the tissue, the water will go inside the tissue of the potato, and the potato will gain weight. And if there is very little different in the two water concentrations, there shouldnÆt be such a big change in weight. And if there is a higher concentration of water in the potato, the water will go out of the potato.

The potato, cut up into pieces, will need some sort of element to survive, and in this experiment, it would be light and water. With both of these sources, the potato will keep on working, until it dies of either lack of water, too much water. When the concentration gradient is lower in the potato, the water will transfer from the solution to the potato. And vice versa.

In the distilled water, I believe that the water is more concentrated in the potato, and therefore the water should transfer from the water to the potato, making the potato bigger in size, and heavier in weight. The potato tissues, being surrounded by a weak solution, will be most likely to swell up and become turgid, taking in all the water it can possibly take in.

With the potato in 0.2 molar solutions of sucrose, I donÆt think there will be much change in the weight of the potato. This is because there isnÆt much difference between the two substances. I believe that the weight and the size of the potato wonÆt be altered much.

The 0.4 molar solutions of sucrose, similar to the 0.2 molar solution of sucrose, compared to the potato, both substances have very close concentration gradients. And that is why I am predicting that the weight of the potato in this experiment should be decreased by only a fraction.

The 0.6 molar solution of sucrose, I think, should make a big difference now, noting that it should be a large difference between the two concentration gradients. And there fore the weight should decrease, at least noticeable for us to notice.

The difference between the water concentration in the potato and the 0.8 molar solution of sucrose is big, and the water in the potato should be transferred from the potato, through the permeable membrane, to the solution surrounding the potato. And as a result, I am sure that the weight of the potato will increase largely. And because the potato tissues are surrounded by a stronger solution, it will probably become smaller, and shrink. But because of such high molars of sucrose, the water can diffuse all the way, throughout the two substances, equaling the concentration gradient of the two substances.

My theory in this experiment is that, due to the difference in the water concentrations of the two substances, I believe that the weight of the potato will start decreasing when it is tested on 0.2 molar solutions of sucrose and greater. By researching information about osmosis, and making predictions of the results, I believe the graph would look something like this:

Fair Test

Fair testing should play a big part in this experiment. If this experiment isnÆt 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 millimeter. 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 donÆt 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 petri dish, and stop the clock as soon as 20 minutes have passed. Stopping the clock, taking æem 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 petri dish 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 isnÆt covered up by the solutions, the effect of osmosis might not occur to the fullest.

Small things such as a dirty petri dish, and a slightly cracked measuring cylinder could still affect the results, and therefore we will take these into account as well.

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 itÆs not handled properly. And we will also be careful that the solutions donÆt 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 werenÆt any bigger matters to be cautious of.

Plan

I believe this task is very simple and should be very easy to carry out the experiment. The investigation is very straightforward.

There wonÆt 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 10mm. And then I will cut the potatoes into cylinders of 30mm x 10mm x 10mm, 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 petri dish.

We will then get 25cm of the solutions and the water with help of the measuring cylinder, and pour them into the petri dish, naming them to make sure that they donÆt get mixed up.

Then we will put the 6 sets of 3 potatoes in the 6 petri dishes at the same time and start the clock running for 20 minutes.

After 20 minutes, we will take all of the potatoes out of the petri dish, 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.

Method

In the actual experiment, instead of using a cork bearer of 10mm diameter, we had to use a cork bearer of 8mm diameter. Although there was a change in plans, I donÆt think this change would affect neither my hypothesis, nor my results that we got.

As for the experiment that we carried out, no changes were made in the experiment.

Obtaining evidence

After the experiment, I had to dry the potatoes first, so that the water outside the tissue of the potatoes wonÆt 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 æsolutionÆ column, which are the 6 different types of solutions. The ænumber of testÆ 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.

Analysis

On the graph shown below, I have made the ædifferent solutionsÆ as my independent variable, since it wonÆt be changing on any event. And I have made the æpercentageÆ as my dependent variable, because it doesnÆt change in any particular order or a pattern. I have decided to make it a bar graph, because the independent variables arenÆt exactly in the same category. For example, I would have used a line graph if the independent variable in my experiment was time, which is changed deliberately, but these is different subjects of matter. And also, the results were very different, as well as the columns and there wouldnÆt be any advantages of using a line graph to view the results. I have taken the average result of the 6 different solutions and put it on the graph to be more accurate.

Conclusion

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 4.62g and 4.87g, 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:

Osmosis actually took place in the experiment.

As the molars increased, the percentage of the weight difference decreased.

There doesnÆt seem to be any results, which undermine my predictions, and our group didnÆt find any anomalous results, which means we didnÆt 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.

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.

Evaluation

We followed the plan correctly, except for the little change that we had to do, which was to use the cork borer with a diameter of 8mm instead of 10mm. But I believe that it wouldnÆt have made much difference to the conclusion. Apart from that small modification in the planning, 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 petri dish 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 wouldnÆt have been very useful, since we had already done the result 3 times, and ALL the results were reliable.

Even though we didnÆt 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 IÆm very please with my results.