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Investigation osmosis in potato cells

Free essay example:

                Muhammad Kermali 10k

                Biology Coursework

Investigating Osmosis in potato cells

Aim:

To investigate the effect of varying the concentration of sucrose solutions and to see if osmosis occurs in potato cells.

Research/definition:

Osmosis is the diffusion of a solvent through a semi permeable membrane from a region of low solute concentration to a region of high solute concentration. The semi permeable membrane is permeable to the solvent, but not to the solute, resulting in a chemical potential difference across the membrane which drives the diffusion.

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 and eventually the internal pressure of the cell is so high that no more water can enter the cell. This liquid 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.

Prediction:

I think that the lower the concentration of sugar in the water, the more mass the potato chip will gain after the experiment is finished.  This is because the water potential in the potato will be lower than the water potential in the solution, and therefore, osmosis will occur, resulting in water being ‘absorbed’ by the potato.

I also think that if the concentration of sucrose in the water is high, the potato will then have a higher water potential than the solution, which will result in water dispersing away from the potato and into the solution, causing the potato to lose mass.

In my experiment, there may be a concentration of the solution which has an equal water potential to the potato, which will result in neither a gain nor a loss of mass for the potato chip as the water would have no preference of location.

Plant vacuoles accumulate enough dissolved compounds to give the plant cell a low enough osmotic potential to absorb water via osmosis.

Preliminary test:

List of apparatus:

List of Apparatus

Why chosen and how used

Beaker

Holds the sucrose solution in.

6 test tubes

Where the sucrose solution is and where osmosis occurs.

Test tube rack

Where test tubes are place in order for them to stand and be used.

Measuring cylinder

Measure how much distilled water and sucrose solution needed.

Labels

So you know which test tube has the correct amount of sucrose solution.

Bores

To cut a cylinder piece potato for the investigation. Simply by placing it on the top of the potato and pressing it down to the end.

Glass rod

To stir the solution and for pushing it in the borer to retrieve the potato cylinder.

Thermometer

To measure the temperature before the investigation starts. Place it in the tube and note the reading

Paper tissues

To dry the potato making sure no other solution is involved.

Weighing machine

To weigh the potato before and after the investigation to see if osmosis has changed it.

Ruler

To find the length before and after the investigation to see if osmosis has changed it.

Scalpel

To cut the ends of the potato leaving only the part you want and the cylinder to the length wanted.

White tile

To place the potato when cutting and after the experiment.

Sucrose solution

This makes osmosis occur and see that difference it has made.

Potato

Needed to see what happens to the potato cells.

Stop watch

To time how long the potato is left for.

Planned/detailed method:

A range of sucrose solutions will be prepared with concentrations 0.2 molar, 0.4 molar, 0.6 molar, 0.8 molar and 1 molar. This will be done by adding varying amounts of distilled water to varying amounts of sugar solution. Sections of potato will be cut using a scalpel and will be measured using a ruler. The chips should also be weighed and dried before the experiment begins. This part of the preparation must be done very accurately as a change in the surface area may allow more or less osmosis to occur. The weight and length are being measured in this investigation. The mass of each chip will be measured before and after so that more results can be obtained and to see if osmosis has occurred. Five potato chips will be placed in each of the five test tubes. They would be labeled so you know which test tube is what solution and how much. The potato pieces will then be placed in specific test tubes and left for 5 minutes with the mixture in their. Then the potato pieces will be removed and dried using paper towels and then re-weighed. I will repeat this experiment 3 times. This will hopefully produce accurate results and an accurate conclusion and graph.

Variables:

To create a fair test, certain aspects of the experiment will have to be kept the same whilst one key variable is changed. I have chosen to vary the concentration of the sugar solution. This will give me a varied set of results from which I hope to make a decent conclusion. If any of the non-variables below are not kept constant it would mean it would not be a fair test. For instance if one of the potato chips was 1cm longer the surface area of the chip would be larger and there would therefore be more space for osmosis to occur. Doing all the tests at one temperature will make it fair.

To carry out this experiment I have to make sure that:

  • That I do this investigation at room temperature.
  • The water potential of the potato initially will be kept the same by using the same type of potato, which has been treated in the same way.
  • The mass of the potato is a dependent variable, and this means that it will be measured throughout the experiment. I will measure the mass in grams. The potato chip will be measured before it is put in the solution, and after. This will allow us to see whether osmosis has taken place, and to what extent.

The volume of the solution that the potato chips are kept in must be fair. The must be totally covered in the solution.

Risk assessment/ safety precautions:

During this investigation, there are a number of safety factors which you have to take into consideration:

  • When using the scalpel make sure the blade is far apart from your fingers in case of a serious cut.
  • Make sure you are using the borer in the correct technique otherwise it could cut you.
  • Make sure a white tile is kept underneath when cutting the potato with the scalpel.

Before the actual experiment, I did a preliminary test so I have a fair idea of what changes I need to make. I also did this as a practice run so I could do my actual investigation quickly and accurately.

Molar

Length(cm)_

Weight(g)

Time(mains)

Temp

0.2

2

0.9

5

17

0.4

2

0.9

5

18

0.6

2

0.9

5

16

0.8

2

1

5

17

1.0

2

1

5

18

Preliminary Results

Before

After

Molar

Length(cm)_

Weight(g)

Time(mains)

Temp

0.2

1.9

1

8

17

0.4

1.8

1

8

18

0.6

1.9

1

8

16

0.8

1.9

0.9

8

17

1.0

1.7

0.9

8

18

These preliminary results give me an overall impression on the change in mass gain or loss when placed in varying concentrations of sucrose solution. However in my actual experiment and in my final method I will keep the chips in the mixture for eight minutes instead of five minutes to get more accurate readings and to let osmosis to occur longer.

Final method and changes made:

  • I took two average sized potatoes and checked that they were both healthy and hard.
  • Using a borer I penetrated the potato all the way through making it look like a long chip and I placed it in a white tile.
  • Using a scalpel I cut the sides of the chips assuring that the skin is not visible during the experiment. Also I used the scalpel to cut the chip into smaller pieces. Each potato chip was 2cm in length.  I kept in mind that a scalpel is extremely sharp and dangerous if misused. I had to be careful when cutting.
  • I dried each potato making sure its completely dry and no other mixtures are involved.
  • I then weighed each potato using an electronic scale and recorded them to see if I had any changes after the experiment.
  • After weighing all my potatoes, I took a test tube rack and place five test tubes labeling them as 0.2, 0.4, 0.6, 0.8, and 1.0. (molar)
  • Using a measuring cylinder I measured out different amounts of sucrose solution and distilled water which I then poured into the test tubes.
  • I swiftly put the 5 pieces of potato chips into each test tube and started my stopwatch. I repeated this investigation 3 times to create an average which gave me a better set of results and more accurate graphs.
  • Whilst waiting I set out some paper towels with which I was going to dry the chips and I drew up a basic table for my results.
  • After 8 minutes I drained out the solutions in the sink and placed all the chips on the paper towel in the order I had put them in the test tubes as to not confuse myself as to which chip came from which solution.
  • I dried each chip with the paper towel and then placed each one on the scales so that I could weigh them.
  • Each potato was measured accurately on the electronic scales and then the weights were recorded.
  • As I had time after doing the first set of results I redid the experiment under exactly the same conditions. This gave me secondary set of results which gave me a more accurate view on the changes.

Measurements and dilutions:

        For this investigation, I am doing 5 concentrations.

0.2 Molar= 18cm3 distilled water and 2cm3 sucrose solution

0.4 Molar= 16cm3 distilled water and 4cm3 sucrose solution

0.6 Molar= 14cm3 distilled water and 6cm3 sucrose solution

0.8 Molar= 12cm3 distilled water and 8cm3 sucrose solution

1 Molar= 20cm3 sucrose solution

Actual results including weight and length changes:

1st run

Before

Molar

Length(cm)

Weight(g)

Time(mains)

Temp

0.20

2.00

1.00

8.00

20

0.40

2.00

1.00

8.00

20

0.60

2.00

1.10

8.00

20

  0.80

2.00

1.10

8.00

20

1.00

2.00

1.20

8.00

20

After

Molar

Length(cm)

Weight(g)

Time(mins)

Temp

0.20

1.90

1.10

8.00

20

0.40

1.80

1.00

8.00

20

0.60

1.90

1.00

8.00

20

0.80

1.90

1.00

8.00

20

1.00

1.70

1.10

8.00

20

2nd run

Before

Molar

Length(cm)

Weight(g)

Time(mins)

Temp

0.20

2.00

1.40

8.00

20

0.40

2.00

1.30

8.00

20

0.60

2.00

1.30

8.00

20

0.80

2.00

1.30

8.00

20

1.00

2.00

1.50

8.00

20

After

Molar

Length(cm)

Weight(g)

Time(mins)

Temp

0.20

1.90

1.50

8.00

20

0.40

1.80

1.50

8.00

20

0.60

1.90

1.40

8.00

20

0.80

1.90

1.40

8.00

20

1.00

2.10

1.20

8.00

20

3rd run

Before

Molar

Length(cm)

Weight(g)

Time(mins)

Temp

0.20

2.00

2.10

8.00

20

0.40

2.00

2.20

8.00

20

0.60

2.00

2.20

8.00

20

0.80

2.00

2.10

8.00

20

1.00

2.00

2.10

8.00

20

After

Molar

Length(cm)

Weight(g)

Time(mins)

Temp

0.20

1.90

2.20

8.00

20

0.40

1.90

2.10

8.00

20

0.60

1.70

2.10

8.00

20

0.80

1.70

2.00

8.00

20

1.00

1.70

2.00

8.00

20


Results showing average changes for mass and length.

Run 1

Run 2

Run 3

Sucrose concentration (m)

Mass

Mass

Mass

Average change in mass

Temp

Before (g)

After (g)

Difference (g)

Before (g)

After (g)

Difference (g)

Before (g)

After (g)

Difference (g)

0.20

1.00

1.10

0.10

1.40

1.50

0.10

2.10

2.20

0.10

0.10

20°

0.40

1.00

1.00

0.00

1.30

1.50

0.20

2.20

2.10

-0.10

0.03

20°

0.60

1.10

1.00

-0.10

1.30

1.40

0.10

2.20

2.10

-0.10

-0.03

20°

0.80

1.10

1.00

-0.10

1.30

1.40

0.10

2.10

2.00

-0.10

-0.03

20°

1.00

1.20

1.10

-0.10

1.50

1.20

-0.30

2.10

2.00

-0.10

-0.17

20°

Run 1

Run 2

Run 3

Sucrose concentration (m)

Length

Length

Length

Average change in length

Temp

Before (cm)

After (cm)

Difference (cm)

Before (cm)

After (cm)

Difference (cm)

Before (cm)

After (cm)

Difference (cm)

0.20

2.00

1.90

-0.10

2.00

1.90

-0.10

2.00

1.90

-0.10

-0.10

20°

0.40

2.00

1.80

-0.20

2.00

1.80

-0.20

2.00

1.90

-0.10

-0.17

20°

0.60

2.00

1.90

-0.10

2.00

1.90

-0.10

2.00

1.70

-0.30

-0.17

20°

0.80

2.00

1.90

-0.10

2.00

1.90

-0.10

2.00

1.70

-0.30

-0.17

20°

1.00

2.00

1.70

-0.30

2.00

2.10

0.10

2.00

1.70

-0.30

-0.17

20°


Analysis and conclusion:

        The graph shown gives the line of best fit for the average change in mass of the potato chips over the course of the eight minute experiment. The graph has a line that crosses from mass gain to mass loss. You can see the line intercepts with the x axis labeled the concentration. That is called equilibrium. This means that the interception point has neither gained nor lost weight. There is a pattern on my graph, and this is, as the concentration of the solution increases, the average change in mass decreases. My prediction was correct. I said that the lower the concentration of sugar in the water, the more mass the potato chip will gain after the experiment is finished. I can prove this because its in my results table showing average change in mass. The graph is evidence to backup my prediction showing it was correct.

        I also said that if the concentration of sugar in the water is high, the potato will then have a higher water potential than the solution, which will result in water dispersing away from the potato and into the solution, causing the potato to lose mass. If you look back at my results table and graph you can see my readings are fairly accurate and reliable. My graph fits and matches my prediction. My graph shows that the potato cells increase in mass in solutions with a high water concentration and decrease in mass in solutions with a low water concentration. This can be rephrased to potato cells increase in mass in solutions with low sucrose concentration and decrease in mass in high sucrose concentration. To show my readings are accurate, you can look back at my graph and see that the interception crosses approximately at 0.5m concentration. This is accurate because the equilibrium is near the middle of the x axis.

        From the point 0.5 there appeared to be no further water loss, suggesting that the cell is fully plasmolysed. This graph of the change in mass helps prove the point of complete plasmolysis, whereby the potato cannot expand and take in any more water. This is because the water potential of the sugar solution is higher than that of the potato chip.  

Evaluation:

The experiment was very successful in my opinion. I obtained a large quantity of very accurate results from which I was able to create informative graphs. I think I took easily enough results for the amount of concentrations that I was using, and the time that I used for the experiment to last was enough to allow sufficient osmosis to occur. However if I was to repeat the experiment I will increase the time of the results to allow more osmosis to happen and possibly find out the saturation point of the chips. The range of concentrations was adequate but I would possibly create more concentrations if I repeated the experiment so that I would have more varied results, i.e. 0.10m, 1.15m, 1.20m, and so on.

The cutting of the potatoes was a difficult part of the experiment, although I was recording my results by mass, it could well have affected the surface area and so the overall rate of osmosis. If I were to repeat the experiment I would have possibly found a machine to cut the potato as it would ensure that all potatoes would be the same weight. As well as the potato I could have found a more accurate way to measure out the solutions and to determine the molar concentrations. This would ensure that I have an accurate amount of fluid in each test tube. I could also weigh each chip on a more accurate scale, e.g. not to 0.00g but to 0.0000g.

If you flick through my graph, then I would say I have a reading which is far away for the line. This anomalous result was 0.80m. This could have been human error faults. When the potato chips were removed from the test tubes and dried I may well have dried some potatoes more thoroughly than others and so some would have more excess water, which would add to the mass. Temperature could have been another factor which could have affected osmosis occurrence. You could extend the investigation by recording the width, height and length before and after the experiment.

However with all this said I think that the experiment was truly successful and I was very pleased with the complete comparison of my results with my initial prediction.  

This student written piece of work is one of many that can be found in our GCSE Green Plants as Organisms section.

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