Investigation of the Concentration and the Effect of Sucrose on Osmosis in Apple and Potato Tissues
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I will be doing an investigation on the topic of Osmosis (A special
type of diffusion).
The aim of this experiment is to investigate the effect of sucrose
concentration on osmosis in apple and potato tissues, to find out how
the concentration of sucrose solution affects the mass of potato and
apple strips. So therefore to find out about the uptake of water into
a cell which depends on two main factors, which are: -
Ø The water concentration of the solution
Ø The water concentration of the cell sap in the vacuole.
Diffusion is a movement of particles from an area of higher to the
area of lower concentration, (by random motion). Osmosis is also a
special case of movement of water, from a higher to a lower water
concentration across a selectively permeable cell membrane until it
reaches the equilibrium.
The process of osmosis makes plant cells swell up as you can see in
the diagram below which shows a higher water concentration outside the
turgid cell, whereas on the plasmolysed cell there is lower water
concentration outside. If a lot of the water leaves the cell, the
cytoplasm begins to peel away from the cell wall; this process is
called plasmolysis. This happens when the water moves into the plant
cell’s vacuole and pushes against the cell wall. In this case the
functions of the cell wall prevent the cell from bursting out. The
process of osmosis takes part in the root of the plant cell, which
takes in water from the soil by osmosis. This leads the water to move
along the root cell into the leaf, and so therefore the water
constantly moves to areas of lower water concentrations.
The process of osmosis also occurs in animal cells, but in an animal
cell there isn’t any cell wall to prevent them from swelling. This
means if they were to be placed in pure water, they would take in
water by osmosis up until they burst, that is called haemolysis, which
occurs only in red blood cells.
PREDICTION (HYPOTHESIS): -
I predict that the mass of the apple and the potato tissue may
increase (rise) in water and dilute concentrations of sucrose
depending on the concentration of sucrose inside the cell. When the
concentration of sucrose outside the cell is the same as the
concentration inside the cell, the mass will remain the same. When the
concentration outside the cell is higher it will decrease the mass of
the apple and potato tissue.
Ø 1x large potato
Ø 1x large cooking apple
Ø 1x sharp knife
Ø 1x metal borer with plunger
Ø 6 Petri dishes
Ø Beaker of distilled water
Ø 50ml of the following molar of the sugar solution: -
0.00M (distilled water) 1.5M, 1.75M, 2.00M, 2.25M, 2.5M (sucrose).
Ø 1x Electronic balancer (for weighing apple and potato strips)
Ø 4-5 pieces of kitchen towel
Ø 1x Wall clock
Ø Blank table of data (to enter the data information and results)
METHOD STEP BY STEP: -
1. Label six Petri dishes 1-6 with the right molar and solution
2. Use the metal borer to produce 18 strips of apple and 18 strips
3. Use the graph paper to measure out all the length of the strips
and make sure they are 20 mm in length.
4. Select three apple strips and three potato strips. Starting with
the apple strips, weigh the first apple strip. Call this apple
strip 1 and record down the weight in grams. Do the same for the
other apple strips and then record the information. Then move on
to the potato strips and use the same method to find out the
weight for each strips, the way it was done for the apple strips.
5. Replace both apple and potatoes strips 1, 2 and 3 and pour 40ml
of distilled water over them and leaves it for 1hour 45minutes.
This Petri dish is the 0.00m sugar solution (e.g. no sugar, 100%
water = 0.00m sugar solution).
6. Repeat the step number four again with the second, third, fourth,
fifth and sixth Petri dishes, but the only difference will be that
the concentration will change. Petri dish two, 0.25M, Petri dish
three, 0.50M and Petri dish 4, 0.75M, Petri dish 5,1.00M, Petri
dish 6, 1.25M sugar solution. Leave all the experiment to run for
7. After doing all this record all the information on the table and
while the experiment is running calculate the average initial
weights of the potato and apple strips for each sugar
concentration (molarity) and record down the data for the average
8. After 1hour 45minutes, carefully pour out the liquid solution
from all the Petri dishes but being careful that the potatoes and
apple strips don’t get mixed up.
9. With a paper towel remove all the extra excess liquid from each
of the strips before weighing them again. Weigh each strip in the
same order as the way done right at the start and then record down
the data under the column of final weight.
10. Calculate the average final weight for each of the sugar
RELIABILITY OF THE RESULTS
Ø The sizes of the all the strips must be large enough to see on
Ø Replicate experiment three times
Ø It should be done in room temperature, because the sucrose may
evaporate because it may affect the rates of osmosis.
Ø The experiment needed to be timed in order to make it a fair test.
Ø Same amount of potato and apple strips.
ANALYSING THE RESULTS
The graph for this experiment results very clear information about the
mass of both the apple and potato experiment. If I compare both of the
results, the apple strip shows more higher percentage in mass and the
sucrose concentration rises quite high in 0.80 sucrose molar and then
from there it keeps decreasing until it reaches to 2.00 molar
concentration. The potato strip however shows a very different result.
From distilled sucrose molar solution it keeps dropping (decreasing)
until it reaches to 1.60 molar, which is the point from when it goes
up nearly 10%.
Apples are sweeter then potatoes so this means it won’t affect the
process of Osmosis. The example for this is photosynthesis. The sugar
in the process of photosynthesis is stored as starch (which is
insoluble), which therefore affect the process of osmosis. It also
attracts animals which therefore disperses the seeds.
The starch is used to give energy for the growth of a new potato, and
the new plants grow from potato tubers through the dotted eyes marked
on the potato skin. In this case it is important that the process
osmosis shouldn’t be used as it will affect osmosis.
Endosmosis is the movement of the water into a cell and exosmosis is
the movement of the water out of the cell. When both endosmosis and
exosmosis are equal it means that the movement of the water into the
cell is equal to the movement of water out of the cell. This point is
called the equilibrium point. At this point the concentration of the
solution surrounding a cell is the equal to the concentration of the
solution in the plant cell vacuole, which is the cell sap.
After plotting all the information on the graph, I have identified
that the equilibrium point is reached at 0.48 molar when endosmosis is
equal to exosmosis for the experiment with the potato strips. However
for the apple strips the equilibrium point is at 1.70 molar. This
shows that the apple strip reaches equilibrium with higher
concentration than to the potato experiment. So therefore this proves
that the apple strip contains more concentrated cell sap than the
potato tissue. The apple concentration is 1.22 molar more than the
potato concentration. However I cannot say it very accurately as there
are some errors in this experiment.
After completing the whole experiment I have gathered a table of
result and a best fit line graph which shows what happened at each
stages of the experiment. In my table I have identified some errors in
the percentage change in mass. One of the figures from both of the
result is quite abnormal. In the apple strip result the 0.80molar
sucrose concentration has -3.3 in its percentage change in mass which
conveys a very low figure compared to the others and so it doesn’t fit
into the data. This is why I have taken out this data because its
anomalies from the rest of the data. I have done the same for the
potato strip result. There was also an anomalies figure in the
2.00molar sucrose concentration, which had -8.8 in the column of the
percentage change in mass. Once again I have taken out this data
because its anomalies from the rest of the information and doesn’t fit
in with them.
I think that the anomalies data may have occurred, due to the amount
in which the strips had weighed after it was taken out of the
solutions. I have decided that it was probably because the water moved
out of the strip which then became plasmalysed.
The actual difference was because the mass was small which increased
the error and also because of the increase in the size of the plant
strip pieces. This is why I would say that the experiment wasn’t
exactly done in a completely fair way, there were some complications.
This experiment has shown quite a variable result in replicates. To
make it more accurate and avoid making the errors I could have made
more concentrations for both the potato and the apple experiments, for
* Potato: - 0.00-0.80 molar
* Apple: - 1.20-2.00 molar
MORE LEFT TO ADD ON ABOUT THE EQUILIBRIUM FIND OUT WHAT IT MEANS AND
EXPLAIN IN DETAIL ABOUT THE DATA USING MY PLAN SHEET.