Essay Color Key

Free Essays
Unrated Essays
Better Essays
Stronger Essays
Powerful Essays
Term Papers
Research Papers




How Osmosis In Potatoes Is Affected By Solution Concentration

Rate This Paper:

Length: 2989 words (8.5 double-spaced pages)
Rating: Red (FREE)      
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

How Osmosis In Potatoes Is Affected By Solution Concentration


Aim

To investigate how the concentration of a salt and water solution
affects the rate of osmosis in a potato.

Osmosis

Osmosis is the passage of water from an area of high water
concentration to an area of lower water concentration, through a
partially permeable membrane (a membrane which allows small molecules
like oxygen, carbon dioxide, water, ammonia, glucose etc to pass
through, but does not allow larger molecules such as sucrose, starch,
protein etc). Cell membranes are partially permeable, which allows
water to pass from one cell to another within the organism, and also,
as I will be exploring in this investigation, from outside to inside,
or vice versa.

Osmosis occurs when the area of liquid outside the cell contains more
water particles than the area of liquid inside the cell. In the
solution, the particles are moving all the time. In a solution in
which the concentration of water is high, there are more water
particles per cm3 than in a dilute solution, and therefore a higher
rate of movement, causing more particles to come into contact with the
membrane. In a more dilute solution in which there are less water
particles per cm3, less movement occurs and therefore less particles
will pass through the membrane. Also, in the solution with low water
concentration, there are more particles of sugar or in this case salt,
which form a weak attraction with the water particles, inhibiting
movement. Therefore, there will be more water moving from the area of
high water concentration.

This diagram shows how osmosis occurs.

[IMAGE]

The diagram shows an area of high water concentration (on the left)
and one of low water concentration. The dashed line at the centre
represents a partially permeable membrane, while the large red circles
symbolize the salt particles and the smaller blue ones, the water. The
arrows show that there are more water particles moving towards and
through the membrane from left to right (high water concentration to
low water concentration) than from right to left (low water
concentration to high water concentration).

Osmosis in plants causes the plant cells to become turgid. A plant
cell has a strong cellulose wall outside the cell membrane-this is
fully permeable. In the centre of the cell, there is the vacuole which
contains the solution of salts, sucrose etc. The thin layer of
cytoplasm surrounding the vacuole is what acts as the partially
permeable membrane. When water enters the cell by osmosis, the cell
swells up; however, the cellulose wall prevents it from bursting. The
wall stretches, but does not break, and eventually the pressure inside
the cell is so high that no more water can enter the cell and the cell
reaches a point where it cannot stretch anymore; we say it is turgid.
(Turgidity is very important in plants, because it allows the
appropriate parts of the plant to 'stand up' in order to get enough
sunlight).

However, if you put a plant cell into a solution of less water
concentration than that inside the vacuole, water is drawn out of the
vacuole. This is known as reverse osmosis. When this occurs, water is
drawn out of the vacuole and the cell shrinks. It loses its turgor and
becomes flaccid. If the external solution is strong enough, the
cytoplasm eventually pulls away from the cellulose wall in what we
call plasmolysis; I do not expect this to occur in this investigation,
as the solutions I will be using will not be strong enough for this to
happen and I will not be leaving it for long enough.

When plant cells are placed into a solution which has exactly the same
osmotic strength as the cells they are in a state between turgidity
and flaccidity; this we call incipient plasmolysis, meaning that
plasmolysis is about to occur.

Prediction

In this investigation, I want to find out how the concentration of the
salt solution outside the potato affects the amount of osmosis taking
place in a certain amount of time (the rate). I think that my results
will show that the lower the concentration of the salt
solution-meaning, a solution with higher amounts of water in it-the
higher the rate of osmosis. I think this will occur because a higher
water concentration has a higher number of water particles in it, thus
there will be more movement of water particles and therefore a faster
rate of osmosis.

I will expect the potato that had been in the strongest solution to
have experienced a slight loss in mass and length, and become flaccid
(feeling soft and 'flabby' to the touch). I expect this to happen
because I expect reverse osmosis to be occuring in this situation,
assuming that the solution is of lower water concentration than that
inside the cell. However, I am making these statements without knowing
the concentration of the solution inside the cell; if the solution
outside the cell is of sufficient water concentration to still allow
osmosis to occur, I would expect to find less osmosis occuring in this
than in situations where the concentration of solution is of high
water content.

I will expect the potato that have been in the weakest solution to
have gained mass and length, and become turgid (feeling hard and
'stiff' to the touch). I think this will happen because I expect a
high amount of osmosis to be occuring in this situation, assuming that
the solution is of higher water concentration than that inside the
cell.

Planning, Ideas and Preliminary Testing

I have performed some preliminary tests in which I set up the
experiment with potato pieces in a solution of low water concentration
and one of high water concentration. The preliminary tests helped me
find out what size of potato pieces to use; I have decided to use
pieces of 3 cm long, because with that size, it is possible to get
three pieces of potato in one boiling tube-this means I can do three
repeats of each experiment. In order to have the potato pieces
completely submerged, I found that I needed to use between 30 and 40
ml of liquid, so I have decided to use 35 ml in order to be sure that
the potato pieces are completely covered.

In my preliminary tests, I found that placing the three potato pieces
one on top of the other was not a good method because it was difficult
to keep them stacked neatly, and the parts of them which were touching
could have affected the rate of osmosis because the area of surface
exposed to the water may have differed from experiment to experiment.
In light of this, I have decided to place the three potato pieces on a
wire, in order to keep them in place and ensure that the whole surface
of each piece of potato is in the solution.

Research on the Internet and in textbooks has indicated to me that a
good time for which to leave the experiments would be one hour. The
book 'Biology For Life' by M.B.V Roberts describes a similar
investigation to the one I am planning to carry out, and states one
hour as being sufficient time for osmosis to occur in small potato
chips.

I am going to use the concentrations 0M, 0.2M, 0.4M, 0.6M, 0.8M and 1M
because I think this gives me a good range of results, and enough
results to enable me to plot a graph. A 0M solution is pure water, and
a 1M solution is a strong salt solution, and I will be using varying
molarities between these in order to be able to plot a graph and see
the effects that different strengths of solution have on the rate of
osmosis.

The way in which I will do the experiment is to measure the mass and
length of 3 pieces of potato, record it, place them (on a wire) in a
boiling tube and add 35 ml of a solution of salt and water. I will
repeat this for different solutions and after one hour, will once
again measure the mass and length of the pieces of potato to see if
there has been a change. I will also measure the amount of liquid left
in the boiling tube, in order to note the change (if any) in this.

I will measure both the mass and the length of the potato pieces
because I think that osmotic action may cause each of these to change,
and this way I will be able to plot two separate graphs. If both sets
of results indicate the same thing, this will add to the reliability
of the experiment because I will have two sets of results to support
my conclusions.

I will make up the solution beforehand using 100ml of liquid overall,
and then measure out 35ml. I will do this because it allows a higher
level of accuracy when it is only necessary to measure out water or
salt solution in quantities like 20 ml, 40 ml etc, which points are
marked prominently on a measuring cylinder, therefore making it easier
to make accurate measurements; if I made the solution to begin with to
35 ml, it would involve measuring quantities such as 27 ml, which
would be more difficult and therefore less accurate than for example
60 ml.

I will dry the potato chips before and after the experiment, to rid
them of any excess water which may add to the mass. I will use
distilled water so it is at a neutral pH and therefore can't affect
the experiment in any way. I will use callipers and top-pan balance
for measuring to ensure precision and accuracy.

I will make sure each experiment is left for the same amount of time
by recording the time each one was begun and measuring exactly one
hour before stopping it. I will leave a few minutes between beginning
each experiment in order that at the end I will have time to measure
the mass and length of each chip.

I will take 3 repeat readings by putting 3 pieces of potato in each
boiling tube; this means that the repeat readings are being done under
exactly the same conditions. Repeat readings ensure reliability
because they allow us to take an average of the three readings.

Method (as for experiment 3, a 0.4M solution)

1. Select an average-sized potato and feel it to make sure it is ripe
and firm. Use an apple corer to cut out a cylinder of potato, making
sure it is at least 3 cm long.

2. Using a calliper, measure the potato cylinder and, using a sharp
knife, cut it to 3 cm long.

3. Use a paper towel to dry the potato cylinder and leave it on the
towel.

4. Repeat with 2 more cylinders from the same potato.

5. Measure the mass of each potato cylinder using top-pan balance and
record it.

6. Impale the potato pieces on a small length of wire.

7. Using a measuring cylinder, accurately measure out 60 ml of
distilled water and put it in a beaker.

8. Measure out 40 ml of 1M salt solution and add it to the beaker.

9. Measure out 35ml of this solution and put it into a boiling tube.

10. Use a thermometer to measure the temperature of the solution in
the boiling tube. Record the temperature.

11. Add the potato cylinders to the solution and put a bung in the
boiling tube.

12. Put the boiling tube into a test tube rack.

13. Record the time at which the potato cylinders were added to the
solution.

14. One hour from this time, unstop the boiling tube and pour the
contents into a beaker.

15. Remove the potato cylinders from the beaker and dry each one with
a paper towel.

16. Measure the mass of each cylinder using top-pan balance and record
it.

17. Measure the length of each cylinder using the callipers and record
it.

18. Repeat with solutions of 0M, 0.2M, 0.6M, 0.8M and 1M.

Equipment List

Potatoes

Apple corer

Calliper

Sharp knife

Paper towels

Top-pan balance

Measuring cylinder

Beaker

6 boiling tubes + bungs

Thermometer

Test-tube rack

Distilled water

1M salt solution

Diagram

Fair Test

There are a number of variables which could affect the rate of osmosis
in a piece of potato submerged in a salt solution. These include:

· Concentration of solution

· Mass of potato piece

· Length of potato piece

· Surface area of potato piece

· Temperature of solution

· Effects of evaporation

· Type of potato

· Amount of time left in solution

· The turgidity of the potato piece to begin with

The variable which we are investigating is the concentration of the
solution, so it is necessary to keep the other variables constant.

The mass and length of the potato piece must be kept the same in each
experiment primarily because they affect the surface area of the
piece, and varying surface area could have a great effect on the rate
of osmosis. This is because in an experiment where the potato chip has
a large surface area, there is a larger area of partially permeable
membrane and therefore more opportunity for water particles to pass
through. I will keep the surface area the same by keeping the mass and
length of the potato piece the same in each instance, by measuring and
cutting it carefully.

The temperature must be kept constant because heat causes particles to
move at an increased speed, which would in turn cause a higher rate of
osmosis because more water particles would be moving through the
membrane in a given amount of time. I will keep the temperature
constant by ensuring to the best of my ability that the conditions and
the room temperature stay the same, and I will prove this by recording
the temperature of the solution both before and after the experiment.

The effects of evaporation could affect the experiment by decreasing
the amount of solution; I will combat this by putting a bung in the
boiling tube to prevent evaporation taking place.

The type of potato could affect the experiment; for example, a sweeter
potato would have more sugar in the vacuole, which makes the water
concentration less than in a different kind of potato. I will make
sure I select potatoes of the same type, roughly the same size and
level of ripeness. Also when selecting potatoes, I will make sure I
choose ones that are generally the same firmness, implying that they
are at similar levels of turgidity.

The amount of time left in the solution is a variable that needs to be
kept the same because we are measuring the rate of osmosis; the amount
that occurs in a given time, and if that time is not constant
throughout the different experiments of the investigation, we are not
getting an accurate picture of the rate. I will keep this the same by,
as aforementioned, recording the time that each experiment begins and
making sure to only leave it for one hour.

Accuracy and Reliability

I will make sure my results are accurate by always measuring correctly
(using callipers, etc, in order to take precise measurements) and by
being thorough with checking the variables and conditions. I will
ensure reliability by taking three repeat readings with each
experiment. I will put the three repeats in the same boiling tube in
order to guarantee that the conditions they are under are exactly the
same.

Results Tables

I will need to fill in a number of results tables throughout my
investigation. I wish to record the temperature of each solution at
the beginning and the end (in order to prove it was a fair test), the
time began and ended (so I can see clearly when I need to stop each
experiment and there will be no confusion leading to anomalous
results), the mass at the beginning and end, the length at the
beginning and end, and the amount of liquid at the beginning and end.
My results tables will look like this:

Temperature

Molarity of Solution (M)

Temp. at start (°C)

Temp. at end (°C)

0

0.2

0.4

0.6

0.8

1

Times

Molarity of Solution (M)

Time at start

Time at finish (after 1 hr)

0

0.2

0.4

0.6

0.8

1

Mass

Molarity of Solution (M)

Mass at start (g)

Mass at end (g)

Change in mass (g)

Average change in mass (g)

0

0.2

0.4

0.6

0.8

1

OBTAINING EVIDENCE

Temperature

Molarity of Solution (M)

Temp. at start (°C)

Temp. at end (°C)

0

18

18

0.2

18

18

0.4

18

18

0.6

18

18

0.8

18

18

1

18

18

Times

Molarity of Solution (M)

Time at start

Time at finish (after 1 hr)

0

9.22 am

10.22 am

0.2

9.25 am

10.25 am

0.4

9.27 am

10.27 am

0.6

9.29 am

10.29 am

0.8

9.31 am

10.31 am

1

9.33 am

10.33 am

Mass

Molarity of Solution (M)

Mass at start (g)

Mass at end (g)

Change in mass (g)

Average change in mass (g)

0

4.3

4.4

4.3

4.4

4.5

4.5

0.1

0.1

0.2

0.13

0.2

4.3

4.2

4.3

4.2

4.2

4.1

-0.1

0

-0.2

- 0.1

0.4

4.1

4.2

4.3

3.6

3.8

3.7

-0.5

-0.4

-0.6

- 0.5

0.6

4.2

4.3

4.2

3.8

3.6

3.8

-0.4

-0.7

-0.4

- 0.5

0.8

4.3

4.3

4.3

3.6

3.8

3.6

-0.7

-0.5

-0.7

- 0.6

1

4.1

4.1

4.3

3.5

3.3

3.6

-0.6

-0.8

-0.7

- 0.7

The next page shows the graph of average change in mass against the
molartiy of the solution.

ANALYSIS

Using my results, I was able to plot a graph of average change in mass
against molarity of solution. I was also able to draw a curve of best
fit, although it is not perfectly smooth; I think this is because of
the scale of my graph.

From my graph, I can see that as the molarity of the solution
increases, the average change in mass of the piece of potato also
increases (although because the change in mass decreased, the graph is
a downward curve; however, it shows that the decrease in mass was
larger when the molarity of the solution was higher). This shows that
reverse osmosis has occurred; the solution outside the piece of potato
has drawn water out from the potato.

This is because the stronger the solution, the less water there is in
it. This means that there is more water inside the cell, and
therefore, because water molecules have kinetic energy, more movement
of water particles inside the cell, causing more particles to move
through the partially permeable membrane because there is an overall
larger rate of movement of particles. Basically, in the experiments
where the molarity of the solution was high, water moved from inside
the cell to the solution, causing the loss of mass in the potato
pieces.

From my results and my graph, I can draw the conclusion that the
molarity of a solution does affect the rate of osmosis; in a solution
with a lower molarity, more osmosis occurs than in a solution with a
high molarity. In a solution with a higher molarity, reverse osmosis
occurs.

My results match my initial prediction, where I stated that I thought
that osmosis would decrease as the molarity of the solution increases.

EVALUATION

In evaluating my experiment, I find that I am not very pleased with
the method and the results I obtained. I did make some changes in the
method when I was actually doing it; for example, I didn't measure the
change in length as I had planned to do, because it was far too
difficult to cut a potato piece to an exact length to the nearest
millimetre, due to thickness of the knife etc, therefore it would not
have been accurate to measure the length afterwards and record the
change in length.

I think my results are fairly reliable because I did three repeats and
took an average; however, the pieces of potato at the start varied in
mass slightly; I found it was impossible to get them all to exactly
the same mass without changing the length. I think this is probably
because the density of the potato is not exactly constant through the
potato, so a piece of potato of the same area may have a different
mass to one from a different part of the potato. There was no way I
could have rectified this, but it did affect the reliability of my
results.

I found I had one anomalous result, that when the solution was of
0.4M, circled on my graph. One can see that it does not fit the curve
of best fit I drew; it shows the same change in mass as that of the
0.6M experiment, which is not how it should be. I think this can only
be because of mistakes made with the measuring either before or after;
if I were to do this experiment again, I would make sure that that
could not happen.

If I were to do the experiment again, I think I would do it using
smaller pieces of potato and larger amounts of solution. Also, I would
perform the repeat readings in separate boiling tubes as opposed to
all in the same one. I would do this because I think it would enable
more osmosis to occur, thus giving me a better idea of how the
concentration of the solution affects osmosis. In this investigation,
the mass of the potato only changed very slightly, and the differences
in the changes of mass were also small. I think if I performed the
investigation with more solution per potato piece, and left it for
longer, it would enable more osmosis to occur and would be a better
portrayal of how the molarity of a solution affects the rate of
osmosis.

Further Investigations

There are a number of further investigations that could be performed
to do with osmosis. One could investigate the effect that surface area
of a potato has on the rate of osmosis; this would be done in the same
way as the investigation which I carried out, except that the molarity
of the solutions would stay the same, and it would be necessary to
change the surface area of the piece of potato by increasing the
length and/or width. I think that this investigation would show that
more osmosis occurs in a piece of potato with a larger surface area,
because there is more partially permeable membrane for the water
particles to go through. One could also investigate osmosis in
different types of potato, or in different types of fruit or vegetable
altogether.

For something completely different, you could investigate osmosis in
animal cells, specifically red blood cells, in which osmosis occurs
when placed into water (this is called endosmosis-the opposite of this
is called exosmosis). You could investigate how the concentration of a
salt solution affects this.

BIBLIOGRAPHY

Biology For Life - M.B.V Roberts

Biology For You - Gareth Williams

The Usborne Internet-Linked Science Encyclopaedia

The Internet (www.google.com for internet searches on osmosis)

How to Cite this Page

MLA Citation:
"How Osmosis In Potatoes Is Affected By Solution Concentration." 123HelpMe.com. 31 Oct 2014
    <http://www.123HelpMe.com/view.asp?id=122116>.




Related Searches





Important Note: If you'd like to save a copy of the paper on your computer, you can COPY and PASTE it into your word processor. Please, follow these steps to do that in Windows:

1. Select the text of the paper with the mouse and press Ctrl+C.
2. Open your word processor and press Ctrl+V.

Company's Liability

123HelpMe.com (the "Web Site") is produced by the "Company". The contents of this Web Site, such as text, graphics, images, audio, video and all other material ("Material"), are protected by copyright under both United States and foreign laws. The Company makes no representations about the accuracy, reliability, completeness, or timeliness of the Material or about the results to be obtained from using the Material. You expressly agree that any use of the Material is entirely at your own risk. Most of the Material on the Web Site is provided and maintained by third parties. This third party Material may not be screened by the Company prior to its inclusion on the Web Site. You expressly agree that the Company is not liable or responsible for any defamatory, offensive, or illegal conduct of other subscribers or third parties.

The Materials are provided on an as-is basis without warranty express or implied. The Company and its suppliers and affiliates disclaim all warranties, including the warranty of non-infringement of proprietary or third party rights, and the warranty of fitness for a particular purpose. The Company and its suppliers make no warranties as to the accuracy, reliability, completeness, or timeliness of the material, services, text, graphics and links.

For a complete statement of the Terms of Service, please see our website. By obtaining these materials you agree to abide by the terms herein, by our Terms of Service as posted on the website and any and all alterations, revisions and amendments thereto.



Return to 123HelpMe.com

Copyright © 2000-2014 123HelpMe.com. All rights reserved. Terms of Service