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The Effect of Osmosis on Potato Cells

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The Effect of Osmosis on Potato Cells



Introduction



Osmosis is the movement of water molecules from an area of low
concentration (lots of water) to an area of high concentration (little
water) through a semi permeable membrane. A semi permeable membrane is
a membrane that only lets selected molecules to pass through it. In a
plant water is taken into the roots by the process of Osmosis. This is
because the cells inside the roots have a higher concentration than
the soil outside the roots. So the water from the soil moves into the
cells by osmosis. When a large volume of water enters the cell, it
swells causing the membrane to push against the cell wall. We say that
the cell is fully turgid. When the water moves out of the cell, the
membrane shrinks away from the cell wall and becomes a flaccid cell.
This causes the plant to wilt, as the cells can no longer provide
support for the leaves.

Equipment

3 test tubes Top pan balance

Test tube rack Tile

10mls of weak sugar solution Labels

10mls of water Scalpel

10mls of Strong sugar solution Ruler

Measuring cylinder Potato

Core borer

Label

Diagram

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Water




Variables

Below is a list of all the variables I can consider to use in my
experiment:

· Have several different concentrated solutions.

· Use different lengths and weights of potatoes

· Have the solution at different temperatures.

· Different volumes of solutions.

· Several potato chips in one solution

Fair Test

To make sure my experiment is fair I am going to:

· Make sure I use the same volume of solution in each test tube

· Have roughly the same size and weight of potato chips

· Same size test tube

· Leave the potato in the test tube for the same length of time

Safety

To make sure my experiment is safe I will wear goggles at all times
and take care when using the equipment, especially when cutting the
potatoes using the scalpel.


Prediction - preliminary plan

I predict that the size of the potato chip placed in the weakest
solution will increase because all the water will move into the potato
cells by osmosis. The concentration in the cells is much higher than
the concentration on the solution. The size of the potato chip in the
water will remain the same because both the concentration in the cell
and in the solution will be the same. The size of the potato in the
strongest solution will decrease because the concentration in the
cells will be lower than the concentration in the solution. Therefore
the water will move out of the cell.

Method - Preliminary plan

1. Collect all equipment.

2. Write out 3 labels, one saying weak solution, one saying distill
solution and one saying strong solution.

3. Place each label on to a test tube.

4. Using the measuring cylinder, measure out 10 mls of each solution
and pour each solution into its correct test tube.

5. Cut out 6 potato chips using a core borer.

6. Weigh each potato chip and make sure all six are 10g, using the
scalpel to help you cut.

7. Place 2 potato chips in the test tube labeled 'weak solution' and
start the stopwatch.

8. Time for 10 minutes and then stop the stopwatch.

9. Carefully take the potato chips out and weigh them, recording your
results.

10. Repeat steps 7, 8 and 9 but this time using the distilled solution
and then the strong solution.

11. In my actual investigation I will follow the above method but
instead used the solutions listed below;

Test tube

Volume of Stock (ml)

Volume of Water (ml)

A

B

C

D

E

F

G

H

I

J

K

10

9

8

7

6

5

4

3

2

1

0

0

1

2

3

4

5

6

7

8

9

10

Results

Results of Preliminary Test

Liquid in Test Tube

Original length of chip (cm)

Final length of chip (cm)

Change in length of chip (-/+ cm)

Weak sugar solution

Water

Strong sugar solution

2

2

2

2.3

1.9

1.8

+0.3

-0.1

-0.2

Results for the 1cm potato chips

Test Tube

Start mass (g)

Final mass (g)

Change in mass (g)

A

B

C

D

E

F

G

H

I

J

K

1.2

1.5

1.4

1.4

1.2

1.4

1.5

1.6

1.3

1.2

1.4

0.8

0.8

0.8

0.7

0.8

1.0

1.0

1.1

1.2

1.3

1.4

-0.4

-0.5

-0.6

-0.7

-0.4

-0.4

-0.5

-0.5

-0.1

0.1

0

Results for the 2cm potato chips

Test Tube

Start mass (g)

Final mass (g)

Change in mass (g)

A

B

C

D

E

F

G

H

I

J

K

2.9

2.6

2.6

2.4

2.6

2.6

2.4

2.7

2.3

2.4

2.3

1.9

1.5

1.5

1.5

1.6

1.8

1.8

1.9

2.2

2.6

2.6

-1.0

-1.1

-1.1

-0.9

-1.0

-0.8

-0.6

-0.8

-0.1

-0.2

0.3

Average of change in mass

Test Tube

Change of Mass (g) for 1cm potato chip

Change of Mass (g) for 2cm potato chip

Average

A

B

C

D

E

F

G

H

I

J

K

-0.4

-0.5

-0.6

-0.7

-0.4

-0.4

-0.5

-0.5

-0.1

0.1

0

-1.0

-1.1

-1.1

-0.9

-1.0

-0.8

-0.6

-0.8

-0.1

-0.2

0.3

-0.7

-0.8

-0.85

-0.8

-0.7

-0.6

-0.55

-0.65

-0.1

0.05

0.15

Analysis

Looking at the results of my preliminary test I had found what I had
originally expected. I predicted that the potato chip in the weak
sugar solution was going to increase in size because the concentration
in the potato cell was much higher than the concentration in the
solution. Therefore the water will move out of the potato cells by
osmosis. In my results the potato in the weak sugar solution did
actually increase in size from 2cm to 2.3cm. There was an increase of
0.3cm. For the potato chip in water, I predicted that the potato chip
was going to stay the same because the concentration in the cell would
be the same as the concentration of the water. I found that the potato
chip actually decreased in size but only slightly. It decreased from
2cm to 1.9cm. I was not surprised to find this, as the concentrations
can not always be exactly the same. The concentration in the cells
must have been slightly lower than the solutions concentration. I
finally predicted that the size of the potato in the strong sugar
solution would decrease because the concentration in the cells would
be lower than the concentration of the solution. Therefore the water
would move out of the cell. The original size of the chip was 2cm, the
size decreased to 1.8 - a change of 0.2cm. So I had predicted
correctly.

In my actual investigation I found that the more sugar in the solution
(stock), the smaller the potato chip was. So if there was a lot of
sugar in the solution then the potato chip decreased in mass. If there
was only a little sugar in the solution the potato chip increased in
mass. This follows the same prediction as the one I made for the
preliminary test.

LOW CONCENTRATION HIGH CONCENTRATION

[IMAGE]

The diagram above can help explain what is actually happening within
the test tube. One side can be the solution and one side can be the
potato cell. The semi permeable membrane, in this case, would be the
cell membrane of the potato cell. When the potato chip is put into a
solution of high concentration, for example solution A (contains a lot
of sugar but little water), the water within the potato cell will move
out of the cell and into the solution. This will cause the potato to
decrease in mass. For example, the potato chip placed in solution A
had an original mass of 1.2g. It had then decreased to 0.8g (refer to
results table for the 1cm potato chips)

Looking at the graphs I found that between solution C and D was where
the potato chip began to increase in mass. I know this because the
line of best fit first slopes downwards but soon as it reaches
Solution C it changes direction and goes upwards. This could be the
point of equal concentration. There was a rough trend running through
all three graphs. As soon as the line reached solution C it began to
increase upward. This happened in all of the graphs. The potato chip
placed in solution K had the highest change in mass. This is probably
because it only had water in it so the water had move into the potato
chip. The concentration in the potato cell must have been lower than
the water solution.

Plants rely a lot on osmosis to support and hold particular organs,
like leaves, upright. Inside the vacuole is a very strong cell sap
solution made up of mainly water containing various dissolved sugars,
salts and chemicals. This is where the water enters during osmosis.
When the cell is placed in a low concentration solution, the water
moves into the cell by osmosis. The cell becomes blown up like a
balloon but is prevented from bursting by the cell wall. We say the
cell is fully turgid. Turgid cells hold the plant upright.

A fully turgid cell

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If the cell is placed in a solution that is of a higher concentration
than the cell sap, water will move out of the cell by osmosis.
Therefore the cell wall can no longer provide support for the plant.
We say that the cell is flaccid. A plant begins to wilt when its cells
are flaccid.

[IMAGE]

A fully flaccid cell

Connecting this theory with my actual investigation, I found that the
before I put the potato chip into the solution it was hard and firm.
This is because the cells were fully turgid, giving the potato support
and strength. When I took the potato chip out of the solution it felt
very soft and limp. This because the potato cells were fully flaccid,
not giving the potato chip any support at all.

Evaluation

Generally, I think my results obtained were fairly accurate. From my
preliminary test I learnt that the three solution was not enough, so I
decided to have 11 solutions instead. I think my decision really
helped because I obtained more varied results, giving me suitable
graphs. This would make the graphs more clear and easier to notice any
trends or patterns. I used the same method I wrote for the preliminary
test for the actual test. During my preliminary test I also found that
leaving the potato chip in the test tube for 10 minutes was not long
enough. So for my actual investigation I decided to keep them in for a
whole night. This would have given us a bigger range between each
result recorded.

If I was to do the experiment again then I think I would choose one of
the solutions and dilute in further. For example:

Test tube

Volume of Stock (ml)

Volume of Water (ml)

H

H1

H2

H3

H4

H5

3

2.9

2.8

2.7

2.6

2.5

7

7.1

7.2

7.3

7.4

7.5

By doing this, it will help me find the cell concentration of the cell
sap solution. It also me give far more accurate results and a more
general idea of what was happening.

During my investigation I found it very difficult to get all the
potato chips exactly the same sizes and mass. I first cut 11 potato
chips to 1cm and the cut the remaining 11 to 2cm. After weighing them
on the top pan balance I found that each chip was slightly bigger or
smaller than the other was (in mass). I did not have time to cut them
further to get them all exactly the same mass. This made the
investigation slightly inaccurate but the differences were not great
enough to cause any major problems.

I do not think it was very fair using two different surface areas of
potato chips (1cm and 2cm). I chose two different sizes so that I knew
which potato chip I was measuring and it also saved time. However, if
I did have time then I think it would have been much fairer if I had
22 test tubes, with only one potato chip inside it.

If we had time then to make the investigation very accurate it would
have been recommendable to find the surface area of the potato chips.
But this involves a lot of time and care and it is very difficult
considering how small the chips are. I would have used the formula,
pr²h, which is the formula to find the surface area of a cylinder.

Looking at my graphs I noticed several anomalous results (circled in
blue on graphs). For example if you look at the graph showing the
average change in mass, you will notice that one result (circled in
blue) looked very odd. This could be due to the inaccurate measuring
of the chips original size. This may have also been the explanation
for all the other anomalous results.

To extend my investigation further it would be interesting to also
investigate what would be the best temperature for osmosis to occur or
whether temperature does or does not effect osmosis. Instead of using
several different solutions, in this investigation you would use only
one, varying the temperature for each one. Using a Bunsen burner, the
solution can be boiled to maybe 15ºC, 30ºC, 45ºC, 60ºC, 75ºC, and left
for about 10 minutes. I know that osmosis does occur after 10 minutes
because it occurred after 10 minutes in my preliminary test. By doing
this investigation we would be able to understand what the best
conditions are, if any, for osmosis.



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"The Effect of Osmosis on Potato Cells." 123HelpMe.com. 28 Jul 2014
    <http://www.123HelpMe.com/view.asp?id=120354>.




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