To Investigate water uptake by Plant Cells

plant cells. This involves Osmosis and the factors that will affect

osmosis are: -

1. Temperature (independent)

2. Time (independent)

3. Size (surface area) (independent)

4. Amount (independent)

5. Weight (dependant)

[7][7]

. Temperature

In an experiment you must always keep the temperature of the

experiment constant otherwise the results will be incorrect, To keep

it a fair test the temperature must be kept the same at all times

because the hotter the temperature is the faster the molecules move.

Therefore if a potato was put in a high concentration of water osmosis

would take place because there is more water outside the potato than

there is in it so the it will diffuse the water from where there is

more to where there is less across a semi permeable membrane. If the

temperature were increased this process would occur much faster.

Here is a diagram showing the speed of molecules: -

[image016.gif] [image017.gif]

2. Time

The experiment has to be kept under a strict time scale. All the

potatoes must be put in at the same time and taken out at the same

time. If not this may result in an inaccurate table of results. If one

is in longer than the other it could result in one having a heavier

weight than it should because it has had more time to pass the semi

permeable membrane.

[8][8]

3. Size

If you have one short potato chip and one long potato chip it wont be

a fair test, since the surface area would be greater and there is more

chance of osmosis occurring through the semi permeable membrane. The

greater the surface area the greater the chance of water molecules

being in the potato so there is a greater chance of Osmosis occurring.

When the surface area is larger there are more cells in contact with

the solution, therefore more gaps for the water to move through.

4. Amount

I the experiment, it needs to make sure that if the result is to be

accurate we have to make sure that the potato is covered in the

solution and it is not exposed to the air. If it is exposed to air

then it will decrease the surface area of which osmosis can occur.

5. Weight

The weight of the potato also needs to be known before it is put into

the solution and we need to know the weight of it after it has come

out of the solution, so we can record a result of the water uptake in

and out of cells. So we will know if the weigh has increased or

decreased.

Each of the above Independent variables above has an effect on the

results. I'm going to investigate the effect of 5 solutions in

varying concentration all 5 potato chips have to have the same surface

area, otherwise more water will be absorbed in some and in others more

water particles will move out into the sugar solution. This then

effects the end weight. All 5 potato chips must be in a beaker/petri

dish or boiling tube labelled A-E, for the same length of time,

because if you leave one in for less time than the other then it has

less time for osmosis to occur so it means the weight at the end is

wrong. All 5 beakers/petri dishes will have sugar in them, however not

of the same concentration. Some will have more and some will have less

and in one dish I will have no sugar in it. The concentrations are as

follows: 0M, 0.5M, 1M, 1.5M, 2M. This means all the potato chips will

have a different weight at the end. Some will have decreased and some

increased.

[9][9]

Prediction

I predict that the potato in petri dish A1 will increase in weight

because the solution has no sugar molecules only water molecules. This

means there is a greater chance of there being more water molecules in

the solution than in the potato, which means the water molecules will

move from the solution to the potato increasing the weight at the end.

In petri dish B1 I predict that the potato will increase in weight

because there are more water molecules in the solution than in the

potato and osmosis is the movement of water molecules from where there

is more to where there is less. I predict that petri dish C D and E

will decrease in weight because there are more water molecules in the

potato than in the sugar solution and osmosis is the movement of water

molecules from where there is more to where there is less, so the

molecules will leave the potato.

Bibliography

I used the following books to help me with my coursework: -

* My school exercise book.

* The essential of G.C.S.E. Double Award Biology.

* G.C.S.E in a week Biology.

[10][10]

Method for Practical

Safety

To make sure that the operation is safe I will make sure that I am

working in a safe environment by: -

· Making sure all chairs and other obstructions are out of the

way.

· Wearing safety goggles and other protective clothing when

needed

· Clearing up any mess made.

· Make sure all bags and coats are out of the way.

· Take all food out of the working environment.

· Dispose of all chemicals and chemical residues safely, with

an awareness of your environment.

· Consider working teammates and their safety at all times.

· Assembling the correct apparatus and materials.

· Be aware of the health and safety rules and regulations.

Check you are working in a safe environment.

Here is the method on which it is going to investigate the uptake of

water by plant cells by changing the concentration.

List of apparatus

* Potato

* Borer

* Electronic scales

* Petri dishes x 5

* Ruler

* Blade

* Sugar solutions (0m, 0.5m, 1m, 1.5m, 2m)

* Paper towels.

* Labels

To keep a fair test

To make the experiment fair I will need to consider the following

factors: -

* The potato chips will need t be kept at room temperature at all

times

* The potato chip must be kept in the solution for the same time as

all of the other chips.

* The surface area of the potato chip will have to be cut with an

effort to make it the same surface area as all the others

What I will need to do

Firstly the environment that is going to be worked must be clear of

all inappropriate objects. Then apparatus will be collected and

assembled correctly.

The potato will then be cut with a borer to produce 5 cylinders,the

borer helps make the surface area constant because it keeps what it

cuts at the same width. The cut pieces of potato will then need to be

measured to 2cm in length and then cut using the provided blade. Once

this process is done the results will be recorded onto a table.

5 petri dishes will then be filled with sugar solution. All 5 being a

different concentration. The dishes will be labelled D0, D0.5, D1,

D1.5, D2 and put A in 0M of solution. B in 0.5M of solution. C in 1M

of solution. D in 1.5M of solution and E in 2M of solution.

Then using an electronic balance the weigh all 5 potato chips will be

weighed separately and the weight of potato A B C D E will be recorded

on a table of results.

Once they are weighed one slice of potato will be placed in every

petri dish with the lid of the dish put on so no dust or other

substances can affect the experiment. The stop clock will then be

started.( potato A in petri dish D0, potato B in petri dish D0.5

etc...).

The experiment will be undertaken in room temperature to make sure the

test will be fair. The potato will then be put into the solution and

left there for 20 minutes.

When the time has reached 20 minutes, the potatoes will be removed

from the petri dish and patted dry with a paper towel. Making sure you

still know which, potato is which potato.

Another experiment needs to be done where the potato's are left in the

solution for 2 hours. After this period of times the weight and length

will need to be recorded.

When the potato's are dry they will then be measured again and then

weighed again, all this will be recorded on a table of results as it

happens.

This whole experiment has to be repeated at least once to make the

results more accurate. The potato's will be labelled A1, B1, C1, D1,

E1. And they will be on a different table of the same style.

Analysis

To Analyze my evidence I am going to study the results from my graphs.

I will start off with my first graph "% gain or loss of weight" and

look at what happened to each potato for the duration it was in the

solution.

Potato A

Potato A after being in the water solution for 20 minutes showed that

there had been no change in its weight, this means that osmosis had

not started to begin. After 2 hours the gradient of the line on the

graph increased, this shows that osmosis has started. This means that

there were more water molecules in the solution than in the potato so

the particles moved from the solution to the potato increasing it in

weight. Water particles move from a high concentration to a low

concentration across a partially permeable membrane(cell wall). Since

the potato in water increased in weight it proves the theory. Then by

24 hours the graph showed that the weight had yet again increased in

weight even more, and the graph showed a steeper gradient i.e. the

rate of osmosis had increased, this tell me that if we had checked the

weight after 48 hours the weight of Potato A was likely to have

increased even more.

Potato B

Potato B displayed on the graph showed me that after 20 minutes there

had been no change, showing that osmosis had not yet taken place. By

the time that the potato was in the solution for 2 hours it still

remained at its original weight showing that nothing has affected its

weight. Even after 24 hours there still has been no change in weight.

I think because no osmosis took place the solution inside the potato

was the same concentration to the solution that it was in.

Potato C

Potato C decreased by 2.20% in the first 20 minutes showing that

osmosis has occurred. This also shows me that the stronger the

solution the faster the reaction is. By 2 hours the weight had

decreased again but at a steeper gradient showing me that the reaction

had quickened up. By 24 hours the weight had increased by not as much

of a bigger leap than before. The gradient was getting shorter,

showing that osmosis was coming to an end.

Potato D

Potato D was in a 1.5 molar sugar solution and it decreased by 3.52%

showing me osmosis had began, this proves my theory stated earlier

"the stronger the solution the faster the reaction." By 2 hours the

gradient of the line had increased and lost over 15% of its original

weight. By 24 hours the gradient had gained a steeper gradient, this

shows me that if the experiment was continued for another 24 hours the

weight would have decreased even more.

Potato E

Potato E placed in a 2 molar sugar solution decreased by the most

(6.31%) in 20 minutes. By 2 hours it had increased in weight and the

gradient of the line was at its steepest, this is because the higher

the concentration the faster the reaction. When the potato had been in

the sugar solution for 24 hours then the gradient of the line started

to fall so the reaction was slowing down. This shows me that after 2

hours the main bulk of the water was extracted from the potato and

osmosis was decreasing i.e. osmosis has nearly finished (diffusion

only stops when the two concentrations are equal ).

The next graph that was drawn up was "% gain or loss of length" and I

will look again at each potato.

Potato A

Potato A before 20 minutes which was in water solution has not changed

its length which shows clearly that osmosis has not occurred because

there was also no weight change before 20 minutes. By 2 hours the

graph showed that the length has increased by 2.86% which shows that

osmosis has started and this is proved by the weight changing before 2

hours. The length seemed to have stopped by 24 hours, this doesn't

seem right when in the weight change graph it seemed to keep

increasing in weight. I feel that because there was an increase in

length there must have extracted water from the solution and the cells

have expanded to fit in this extra solution. i.e. extra molecules.

Which gave the potato more space to gain weight by extracting more

water.

Potato B

Potato B stayed at its original length all the way through the

experiment. This is because osmosis did not take place. This proves my

earlier theory of this potato being in a solution that is to the same

concentration as inside the potato.

Potato C

Potato C decreased in length before 20 minutes, which I would have

predicted that it would have because it fell in weight before 20

minutes in the weight change graph. From 20 minutes all the way to 24

hours there was no change in length at all. Which seems strange

because the weight was increasing rapidly.

Potato D

Potato D Decreased in length by 2.86% before 20 minutes which was the

same for potato C. The length then kept constant till 2 hours when it

decreased (5.86%). I think this was because the weight decreased so

much so the cells shrived up. When the potato was taken out of the

solution after 24 hours it was all limp and soggy this was because all

of the most was extracted from it.

Potato E

Potato E lost the most length by 20 minutes. This matches the weight

change graph because the most weight was lost in this time too. From

the 20 minutes onward the length kept constant, this is because it had

already lost so much length and it showed in the weight change graph

that osmosis was ending, so the length would not need to decrease any

more.

The next graph that was drawn was "Average % change graph for weight"

of both experiments that were taken out and I will be looking at the

average results that I have found from both experiments for an overall

result.

Analyzing this graph, it shows me a better view of what happened to the

potatoes. It shows that potato A needed more time for osmosis to finish

because the gradient of the line was still increasing by 24 hours. Potato B

increased slightly and kept at a constant weight throughout the experiment,

which shows me that osmosis finished quite early in this potato. Potato C

Showed that the gradient was getting shorter, showing that osmosis

was coming to an end. This was the same for Potato D and E, so it

shows me that osmosis had nearly finished by 24 hours.

The next graph that was drawn was "Average % change graph for length"

of both experiments that were taken out and I will be looking at the

average results that I have found from both experiments for an overall

result.

Analyzing this graph I find that it give clearer information than the

other experiments. It shows accurate results for Potato A and C but

not so accurate results for the other potatoes. It shows that potato B

has lost length when in the Average weight graph it shows an increase

in weight. In potato D and E it shows that after 2 hours they decrease

in length when in the average weight graph they stop gaining weight

after 2 hours. This may be because the cells think that osmosis is

still taking place.

From all of my result, I have found how osmosis reacts in different

water solutions: -

0m (water)- the potato increases in weight and in length. This is

because there was a higher concentration of water molecules outside

the potato so diffusion occurs extracting water particles from the

solution through a semi permeable membrane until the water particles

are equal either side of the semi permeable wall.

0.5 m- 1m (weak sugar solution) - there is virtually no change in the

potatoes weight and length indicating that no osmosis took place

because the solution inside the potato was the same concentration to

the solution that it was in.

1.5m - 2m (strong sugar solution) - There was water moved by osmosis

from the potato to the solution because there was a greater

concentration of water molecules inside the potato cells than in the

solution so osmosis takes place and the potato decreases in weight and

length.

Also from my results I found that the rate of the reaction occurred

faster when there was a stronger sugar solution. I believe that this

was because there was a steeper concentration gradient between the

potato and the sugar solution so more water in the potato cells that

in the stronger solution so the water was extracted from the potato

cells at a faster pace.

These results confirm most of my original prediction that potato A

will increase in weight because "the solution has no sugar molecules

only water molecules." My results did prove that potato B would

increase in weight but it did not prove that there would be a decrease

in length, I think that this decrease in weight may just have been a

human error of judgement. Potato C,D and E were all confirmed in the

prediction to being the same in my results by the fact that they all

decreased in weight.

Evaluation

I am pleased with the results that I have found from my experiment to

find the uptake of water by plant cells. I feel that I have reached

all my aims in this project and have found how and why plant cells

uptake water.

Looking at the accuracy of my result I feel that it went well because

all my results were at a satisfactory standard, I even repeated the

experiment for improved accuracy and made two average graphs to make

an overall result. When I look back at my graph in the first

experiment I found that the % gain or loss of length was not as

accurate as the second experiment. I feel this because in the second

experiment I had a wider range of values and the graph was more spread

out. The average % gain or loss graph of length averaged out the

results giving me a better result.

I feel that all the procedures that were taken out were done under

great precautions of accuracy, one of the faults that did occur was

that the timescale was a bit wrong, in the sense that we could not

return to our experiment on the exact time that we were suppose to,

this was because it clashed with other lessons. Another fault was the

human error, because nobody is 100% accurate in the sense that reading

off apparatus and measuring objects can never be 100% accurate.

I do think that the evidence that we did record was at a good standard

of accuracy and it does provide enough evidence to draw a final

conclusion. My work proved that the concentration of the solution

affects the direction of movement in water. This happens because

water molecules move from a dilute solution to a concentrated

solution. It also enabled me to form a valid conclusion about osmosis.

A gain in weight occurs when every cell takes in water, therefore

every cell gets larger and heaver. A loss in weight occurs when water

leaves the cell to go into the solution.

I feel that this project and procedure did need improvements in the

sense that I feel we needed more time because it would mean that I

could do more repeats of each sugar solution and therefore there would

be an increase in accuracy which would enable me to obtain more

conclusive results. Another improvement would be to split up the class

into 2 groups to do the experiment at different times, this would

increase space and make it easier to carry out the experiment

satisfactorily. As it was I found it quite cramp and busy and this

hindered me in carrying out my experiment.

_______________________

[11][3] Deri Reed

Chemistry Coursework

Mrs. Sanders

[12][4] Deri Reed

Chemistry Coursework

Mrs. Sanders

[13][5] Deri Reed

Chemistry Coursework

Mrs. Sanders

[14][6] Deri Reed

Chemistry Coursework

Mrs. Sanders

[15][7] Deri Reed

Chemistry Coursework

Mrs. Sanders

[16][8] Deri Reed

Chemistry Coursework

Mrs. Sanders

[17][9] Deri Reed

Chemistry Coursework

Mrs. Sanders

[18][10] Deri Reed

Chemistry Coursework

Mrs. Sanders

References

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