Biology Osmosis Plan

Biology Coursework

Concentration inside a potato cell

Plan

In this experiment, I will investigate the concentration inside a potato cell; through the process of Osmosis. This is the movement of water down its concentration gradient across a living cell membrane.

Using certain concentrations of sucrose and water, I will discover, further, the concentration of sugar within a potato.

To begin with, I will do a preliminary test. This will be to see the general outcome.

Then I will note down the results and compare them with the actual results that I will do a week later.

The variables in this experiment are:

Temperature should be controlled as osmosis works faster in higher temperature. I will keep the temperature the same at all times. I will therefore be doing all the experiment in one day, at one hour.
Surface area of the potato chip. This will need to be controlled as the different sizes may have different concentrations and will be an unfair test. To ensure this I will use the same size borer as the borers are of different sizes. I will also choose relatively same size potatoes.
Concentration of sucrose, which is the dependent variable in this experiment. This will be altered in order to complete the experiment.
Timing for experiment, if longer then I should expect to see a different mass change. This should be kept constant, in my case it was 20 minutes this was kept the same, throughout the three experiments.

Here is a diagram of my potato cell.

This is a typical plant cell. The vacuole is where the sugar is held and this passes through the cell membrane and cell wall. This is the process of diffusion. Diffusion is when there is movement of gas naturally. For example, if a stink bomb was set off in room A, and the door was opened going through to room B then the smell will go there as well.

Here is a diagram to show diffusion.

My equipment in this experiment will include:

- Sucrose to see the change in mass.

- Potato (3 large)

- Borer to take out some of the potato

- Smaller Borer to take the potato out the larger borer

- Test tubes for the reactants and the reactions to take place.

- Wash bottles to add distilled water in the test tubes

- Measuring cylinder to measure the correct amounts of sucrose and distilled water.

- Stop watch to time the time for the experiment.

- Scales to measure the mass of the potato.

- Knife to peel the bits of potato I did not want in the experiment.

-Test tube rack to hold the test tubes whilst reacting.

- Tile for the potatoes to lie on whilst measuring.

Prediction

This is a preview of the whole essay

-Test tube rack to hold the test tubes whilst reacting.

- Tile for the potatoes to lie on whilst measuring.

Prediction

I predicted that the more concentration of sucrose in the test tube, the mass after would be less than at the start. I think this because of the scientific theory of ‘Osmosis’. This is the theory that states when a concentrated item (in our case a potato chip) the sugar concentration within that will move out to the more concentrated position. I think that as the sucrose is added to the beaker, then the potato chip’s sugar concentration will move out to this solution, which will have a higher level of concentration of sugar compared to the potato chip, and as the concentration is being moved then the mass will be affected greatly.

Here is a diagram to show my view along with the osmosis theory.

It states that the 1.0 molar-concentrated item will move out to the 2.0 molar concentration and the 3.0 molar concentration. Whereas the 2.0 molar concentration will only move out to the 3.0 molar concentration. The 3.0 molar concentrations will not go anywhere as that is highest concentrated.

However, if the concentration of the solution is 50% of sucrose and 50% of distilled water, then there should not be such a great mass change as the potato chip and solution surrounding it will be equal.

Here is a diagram to show my view along with this theory:

As you can see that, the potato would be unlikely to lose or gain mass.

Through the Osmosis theory and my view, I expect the graph to show the percentage increase or decrease in mass of the potato chip.

To summarise, I believe that the more concentrated the solution the less mass the potato will have at the end of the experiment. The less concentrated solution then the more mass the potato will have at the end of the experiment.

Here is my prediction graph:

As you can see that the decrease in mass has been proven by the fact that the 1.0M of sucrose has decreased in mass, having a 12.5% decrease. This proves the theory of Osmosis. The solution surrounding the potato chip is known as a hypotonic solution, in this situation osmotic pressure leads to the migration of water into the cells.

To begin the task I firstly did a preliminary experiment. Containing only three test tubes. Test tube 1, which was 1.0M concentration of sucrose with the potato chip, test tube 2 that was 0.5M concentration of sucrose and water with the potato chip, and test tube 3, which was, just distilled water with the potato chip. My results showed that the more concentrated solution had the potato lose its mass.

Here is a graph to show the preliminary results:

Method

To begin with, I will prepare my apparatus, by simply taking my test tube rack and setting five test tubes in it, I will then set up a measuring cylinder with 20cm3 of sucrose in it.
I will then use the borer to penetrate through the potato, I will do this, and using the second smaller borer, I will take out the potato, which will still be inside the borer. I will do this 5 times. However, since the skin will be left on the potato I will use a scalper to remove the skin on each potato chip.
I will take my potato chips and measure them using the measuring scale. I will make sure that each potato chip is the same mass as the others. If not I will cut them down to make sure that it is.
From this, I will go on to pouring the 20cm3 of sucrose into test tube 1. Then I will label this test tube, (using a marker pen and stickers) 1.0M.
Following this, I will go on to measure 15cm3 of sucrose and 5cm3 of distilled water using the measuring cylinder. I will pour each solvent into the test tube 2, and label this test tube as 0.75M.
From here I will measure 10cm3 of sucrose and 10 cm3 of distilled water, I will then pour these liquids into test tube 3, and once again label it as 0.5M
After doing that, I will measure 5cm3 of sucrose and 15cm3 of distilled water. Then I will label this test tube as 0.25M.
I will then measure 20cm3 of distilled water in the measuring cylinder and I will pour this into the test tube 5, and I will label it as 0M.
After this is complete, I will have my measurements and my chips, so all that will be left to do is to put the chips in the test tubes. However, to ensure a fair test I will have to put each chip in each test tube simultaneously and begin the timing as well. To do this I will use another person, he will have two chips and I will have three, we will manage to put them in simultaneously as well as time them as soon as they have been inserted.
From here, I will time 20 minutes using the stopwatch.
Once the twenty minutes are up, I will quickly take each one out and lay it on a tile. Still keeping them in order, I will weigh them once again.
Once I retrieve my results, I will note them down.
After this I will begin the same exact experiment again, using different potato chips, by making new ones but still keeping the same mass.
After that experiment, I will do another the same. This will be to get an average so my experiment will be a fair test.

In order to keep a fair test, I did the experiment 3 times. This was to get an average, as I could not rely on just one set of results.

In terms of safety, I made sure that the scalpers were used only when necessary and those they were not a danger to anyone else.

My results will be accurate as everything was done accordingly. My method clearly shows I completed the experiment in a sensible and accurate way. Measuring out each solution was done accurately as well. Potato chips and masses were all the same so no unfair test was taken.

Results

My results clearly show that the accuracy was done very well, but improvements are essential. As you can see from the graph that there is a trend. A negative correlation, the pattern is that every concentration the mass is decreasing. My graph explains the theory of osmosis, the decrease in mass after the lower concentration moves to a higher concentrated area. This graph shows that the more concentrated solution surrounding the potato chip has had the potatoes concentration diffuse through.

Clearly, it shows that the concentration 1.0M has lost its mass by approximately how much the distilled water has gained its mass, the 1.0M mass change was -14.64%, a decrease and the 0M (the distilled water) had a mass change of 16.02%, an increase. This is because the distilled water has little concentration of sucrose and so this diffuses to the potato.

This is known as water potential.

Water molecules move randomly. When water is enclosed by a membrane, living or artificial, some of the moving water molecules will hit the membrane, exerting pressure on it. This pressure is known as water potential.
As the number of water molecules increases, the number of collisions between the molecules and the surrounding membrane increases. This causes the pressure on the surrounding membrane to increase so the water potential will increase.

When the concentration was 0.5M, you can see that the result shows very little mass change average mass change being 0.28%; this is isotonic solution, which means an equal solution. The concentration within the potato and the solution surrounding it is very similar. This intercepted the x-axis, as the percentage increase/decrease was averaged to zero. My results were accurate, and the way I planned it proved this. I accept the original hypothesis as they fit the predicted graph. E.g., the percentage increase was 12% in the predicted graph using the scientific knowledge, and in my experiment, it was 16%, these are very close. The decrease part however, was even closer as in the prediction it was 12% and in my experiment it was 12%.

Evaluation

My method was very accurate, as it clearly defined what was required to keep the test fair. There were no sources of error, as my results have proven correct. There was one anomaly. This was due to the lack of drying the potato down, without drying it; I think it increased the mass however, I did not include this whilst taking an average; I was unable to re try this result due to a lack of time. This was done on the 0.5M sucrose potato chip.

However, I believe that my experiment could have been done better with the aid of higher technology. For example, the measuring scale could have been better, giving a more precise reading, at least three decimal places. Other than that, my experiment could have been improved by drying the potato chips out better as water may have lain on the mass scale increasing the mass. In addition, this could have affected my results.

Equipment, I think that the measuring cylinder could have been better as it was hard to read exactly what the result was. The timings were important, as one extra minute could have changed the whole result. Therefore, I think that by using extra persons then the experiment could have been more precise and accurate.

In my experiment, there was only one anomaly and it was due to not drying out the potato properly and wiping the scale clean of the solution.

To investigate further I would take different size potatoes with different masses but still using the same sucrose concentrations. This would prove the Osmosis theory further. As well as this I would also be inclined to try out a different potato and see the theory in that case, different potato in the sense of a different brand or a different make. This would be an interesting view at Osmosis. Other than that, I would also be interested if a new sugar concentration was introduced. This way I could find out if the theory works with different sugars and different potatoes. I would also investigate by trying the experiments in more detail. Using higher technology and more advanced equipment, to measure and to add concentrations. This would provide additional evidence to the Osmosis theory.

Conclusion

In an overall aspect my experiment was done with precision and accuracy. I have learnt that Osmosis is the theory that states a less concentrated will move to a higher concentrated solution.

With the aid of further technology I think that the experiment could have been done more specifically.