To investigate how the concentration of sugar and surface area of cut potato tubes affects potato cells

Fair test

To make this a fair test some simple procedures will have to be done. I will have to make sure that all the potato tubes are the same size and that I put the same amount of liquid in both of the beakers (100cm3) beakers... I will also have to keep at the beakers in the same place so that temperature and light does not affect the results I would be recording. To make the measuring of the potato tubes accurate I will use an electric scale to two decimal places. This would give me accurate readings. I will keep all the potatoes in the beakers for the same amount of time or this would clearly affect the results because some tubes of potato would have more time to lose or gain mass. I will also repeat the experiment twice and even compare my results with other people to ensure my results are as fair as possible.

Safety

To make the experiment safe, all I can do is carry out the obvious. This includes tucking in stools and placing bags under desks. I must stand when doing the experiment and never run for any reason and not cut the potato on my hands.

Apparatus

Beaker (100cm3)

Measuring cylinder 10cm3

Potatoes

Cork borer

Sucrose

Distilled water

Electric scales (gram to 2 d.p.)

Knife / Tile

Diagram

Sucrose Water

Solution

Beaker (100cm3) Potato tubes

Potato tubes

Beaker (100cm3)

Results table

Concentration of solution

Mass of potato before

Mass of potato after

Change in mass

average change in mass

Average mass of potato before

Average mass of potato after

Percentage increase/

decrease

Without sugar

2.8

4.47

.64

.04

3.16

3.72

21%

2.7

3.14

0.44

With sugar

2.9

2.1

-0.8

-0.86

2.9

2

-30%

2.9

2.0

-0.9

Graph

Below is a bar chart that shows the extent by which the potato tubes change mass in sucrose solution and distilled water. I have also shown average change as I did the measurement twice in each solution. I therefore assumed that my results were fair as both sets showed similar changes. The potato tubes in sucrose solution went down in mass while the potato in distilled water went up in mass. These results agree with my hypothesis and predictions. The potato tubes must contain a certain amount of their own sucrose solution in order for water to move through osmosis either way.

Conclusion

During this investigation I have found out that osmosis does occur in potato cells. When the concentration of the sugar was low, the solution was taken into the potato cell and this is why there is an increase in mass. When the concentration was high in the outside of the solution, solution from the potato cell was released as it tried to balance out the concentration inside and outside the cell. As stated in my introduction, solutions move from a destination of low concentration to an area of high concentration. I know that solution was released or gained because the mass of the potato tube increased or decreased. It was also visible that the potato tube had changed size. The potato that had lost mass had got smaller by 2mm but the potato tube that had gained mass had got bigger by 4mm. I think if I were to do the experiment again I would take more readings and look out for any anomalous results.

Evaluation

I think the procedure I used was not as accurate as I would have liked because I could not measure exact surface area of the potato tubes.

To take potato tubes from the same part of the potato would also be a sensible idea because the concentration of cell sucrose may vary between the outside and the centre inside the potato. I think I took enough results to make a conclusion but with more time, I could repeat the experiment using different concentrations of sucrose solution to get even more reliable results and perhaps to work out the sucrose concentration inside the potato. That concentration is when water does not move in or out of the potato and so it will not change mass or size.

The investigation could be extended. Different types of potatoes could be used. This would show different effects of using the different kind of potato cell that may contain different sucrose concentrations. This therefore, may affect the rate of osmosis.

Investigation 2 - surface area effects of the potato in water

Introduction

It is known that liquids move from a low concentrated area to a higher concentration. This is more commonly known as osmosis. The liquids try to balance out the concentration.

Osmosis occurs commonly in cells. Substances such as water are diffused into the cell until the concentration from the outside and inside of the cell are as equal as possible.

Prediction and hypothesis

If the concentration of the cell is higher than the surrounding liquid, water, will pass through the cell membrane into the cell until the concentration is equal as possible. In this case the cell may increase in size and therefore weight. The speed of this process will depend on the surface area of the potato exposed to the surrounding liquid.

I predict that if I double the surface area exposed in water, then the speed of osmosis will also double. This means the potato will increase in weight faster because water tries to enter its cells and dilute the sugar content inside.

Plan

I will first collect the apparatus shown in the apparatus list and set it up according to the diagram. I will punch 6 holes with a cork borer and collect the 6 tubes of potato as evenly as possible. I will leave one tube intact and I will cut the second in two, the third in three, the fourth in four, the fifth in five and the sixth in six. I will weigh each potato sample before starting the experiment and record the results. I will put the potatoes into their individual six beakers. I will add 75cm3 of distilled water to each beaker. After I have done this, I will label each of the beakers. I will leave them for a day.

When I return to them I will dry of the potato samples making sure they stay in order. I will then re-weigh the potato samples and record these results. After doing this I will find out how much the weight has changed and by what percentage. I will then try to link this with the explanation of osmosis to see if there is a link between more surface area and increase in overall weight after a day.

Safety

To make the experiment safe, all I can do is carry out the obvious. This includes tucking in stools and placing bags under desks. I must stand when doing the experiment and never run for any reason and not cut the potato on my hands.

Apparatus

Beaker (100cm3)

Measuring cylinder 100cm3

Potatoes

Cork borer (5mm)

Distilled water

Electric scales (gram to 2 d.p.)

Knife / Tile

Diagram

Water Water

Beaker (100cm3) 2 Potato tubes

1 Potato tube

Beaker (100cm3)

Water Water

Beaker (100cm3) 4 Potato tubes

3 Potato tubes

Water Water

Beaker (100cm3) 6 Potato tubes

5 Potato tubes

Beaker (100cm3)

Results table

BIBLIOGRAPHY

Results table

Potato sample

(1 or 2) and number of pieces

Mass of potato before

/ g

Mass of potato after

/ g

Change in mass

/ g

average change in mass

/ g

Average mass of potato before

/ g

Average mass of potato after

/ g

Percentage increase/

decrease

%

= 1 piece

.25

.324

+0.074

+0.0395

0.9175

0.957

+4.305

2 = 1 piece

0.585

0.590

+0.005

-

-

-

-

= 2 pieces

.39

.515

+0.125

+0.08

.0225

.1025

+7.82

2 = 2 pieces

0.655

0.690

+0.035

-

-

-

-

= 3 pieces

.32

.435

+0.115

+0.0815

.001

.0825

+8.14

2 = 3 pieces

0.682

0.730

+0.048

-

-

-

-

1 = 4 pieces

.30

.438

+0.138

+0.1195

0.955

.074

+12.5

2 = 4 pieces

0.609

0.710

+0.101

-

-

-

-

= 5 pieces

.33

.468

+0.138

+0.0805

0.9935

.074

+8.10

2 = 5 pieces

0.657

0.680

+0.023

-

-

-

-

= 6 pieces

.52

.661

+0.141

+0.0715

.049

.1205

+6.82

2 = 6 pieces

0.578

0.580

+0.002

-

-

-

-

BIBLIOGRAPHY

Class notes

Understanding biology by Glenn Toole and Susan Toole, Published by Stanley Thornes.

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