Aim: To investigate the process of osmosis in potato cells.
Biology Coursework Planning - Osmosis in Potatoes
Aim: To investigate the process of osmosis in potato cells.
Key factors and planning an investigation which is a fair test
The different factors which affected the process are:
* Using 2 potatoes, so tubes came from different potatoes.
* When drying the potato cylinders for excess solution, some of the tubes may have been dried more, so therefore will weigh less.
* When cutting the potato tubes, some of the cells may have been damaged.
* The potato tubes were not put in the solution at the same time, so some tubes start osmosis before other tubes making it unfair.
* The shape of the potato.
The different factors which I will be trying to keep the same are:
* Measuring the same amount of solutions in each test tube.
* Cutting the potato tubes all to the same length.
* Using all three tubes from the same potato.
* Making sure that I put all three tubes into the test tubes at the same time.
The factors which are going to be beyond my control are:
* The temperature conditions.
* The pressure of the solution
* The volume of the solution
* The surface area of the potato
Prediction & Background
I predict that the mass of the potato in a sucrose solution will decrease because water will diffuse by osmosis. However the mass of the potato in water will increase because water is moving into the potato and making the sucrose come out of it. This will balance the concentrations. The potato from a solution with more water will weigh more than one from a solution with less water because there will be more diffusion of water molecules where there is lower concentration. The water molecules can get through the partially permeable membrane because they are small and can easily move in to the potato. However, the sugar molecules are much larger and cannot therefore move out of the potato unless pushed out by water molecules. The more sucrose present in the solution, the less weight will be gained by the potato cylinder, or sometimes weight will even be lost, and that at lower sucrose concentrations, the percentage change in mass of the potato cylinders will be higher. This is because water molecules will randomly spread out, diffusing from an area of high water concentration, to an area of low water concentration. Certain cylinders will gain mass, because they will take in water through osmosis, as they are the cylinders which are placed in weak sucrose solutions, and so therefore the amount of water molecules inside the cylinder, is less than the amount around it. This is also why some cylinders lose mass, or do not gain as much as others, as they are in stronger sucrose solutions.
Preliminary Apparatus:
Equipment
How and why was it used?
One potato
I used one potato because then all the pieces would have the same amount of sucrose.
One potato borer
I used this by pushing it through the potato, which cut out thin cylinders from the potato very easily
Scalpel
A small, safe knife to cut small amounts off the potato cylinders. So that all the cylinders were of equal length.
Glass rod
Used for removing the potato cylinder from the potato borer, pushing it gently out from ...
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Preliminary Apparatus:
Equipment
How and why was it used?
One potato
I used one potato because then all the pieces would have the same amount of sucrose.
One potato borer
I used this by pushing it through the potato, which cut out thin cylinders from the potato very easily
Scalpel
A small, safe knife to cut small amounts off the potato cylinders. So that all the cylinders were of equal length.
Glass rod
Used for removing the potato cylinder from the potato borer, pushing it gently out from the bottom, without breaking it.
Boiling tubes (x3)
Larger test tubes, making it easier for me to remove and add potatoes and liquids.
Squeezy Bottle
A bottle full of water with a tube coming out from the top. When pressed, it squirts water into the measuring cylinder to the amount of volume needed.
Beaker
Used to hold the sucrose solution so that there was enough for me to use.
One Permanent Marker
For writing our names on the test tube rack, writing the amounts of molar solution on each boiling tube.
Pipette
Used for putting and taking out the right amount of sucrose solution needed, in each boiling tube.
Test Tube Rack
To hold all three boiling tubes with a potato cylinder and molar solution in each one.
Ruler
To measure the length of each potato cylinder, making sure they were all the same length.
Stop clock
To time how long the experiment took and note what time I started and finished.
Measuring Cylinder
Used to get accurate volumes of water and sucrose solutions so that the amount of solution in each boiling tube would be the same.
Scales
This also has a Petri dish on it to weigh the potato cylinders.
White Tile
For when I was using the potato borer to cut out cylinders, so that I wouldn't cut myself.
Clingfilm
To wrap my boiling tubes with, after I've put the potato and the right solutions in.
www.intst.net/science/study_pages/igcse/biology/01_cells_enzymes/osmosis3.gif
Preliminary Method:
) First I used the potato borer to cut out three potato cylinders from one whole potato. I removed the cylinders from the potato borer, by poking a glass rod through the borer, which gently pushed the potato cylinder out from the bottom of the borer.
2) Then I cut all three potato cylinders to the exact same length with a scalpel, using a ruler to measure the length and then cutting it. My lengths for the potato cylinders were all 5.5cm.
3) After performing the length of the potato cylinders, I performed the mass of them on a weighing scale. Getting them to weigh the same, as close as possible. Making sure they all weighed around the same gram.
They all weighed around 4grams.
4) I then added the appropriate amounts of volumes into the boiling tubes. 0M-all water, 0.5M-half water and half sucrose, 1M-all sucrose. Each boiling tube had a maximum solution of 20cm³.
* Boiling tube with 0M - 20cm³ of water
* Boiling tube with 0.5M - 10cm³ of water and 10cm³ of sucrose
* Boiling tube with 1M - 20cm³ of sucrose added one potato
5) After adding the solutions shown above to the three boiling tubes by
using the squeezy bottle with water in it and a syringe for collecting the
sucrose solution from the beaker, I measured these in a measuring
cylinder to get the right amount of volumes.
Also labelling each molar solution on the boiling tubes with a permanent
marker so that I knew which was which, I added one potato cylinder to
each boiling tube. Making sure that each one was fully covered in each
solution. I tried to put all three potato cylinders in at the same time. So it
would be fairer if all of them started osmosis at the same time.
6) Next, I covered each boiling tube with a cling film, so that nothing would affect my experiment of osmosis. Also nothing would evaporate from the potato causing the concentration to increase.
7) I then left these boiling tubes on a test tube rack with my name on it, for a few hours until osmosis had occurred in the potatoes.
Preliminary Results:
Molar Solution (M)
Mass
Before (g)
Mass
After (g)
Length
Before (cm)
Length
After (cm)
0
4.49
5.09
5.5
5.8
0.5
4.45
3.81
5.5
5.1
4.51
3.06
5.5
5.0
Water Solution
Molar solution (M)
Volume Before (ml)
Volume After (ml)
0
20
9
0.5
20
21
20
22
I used a different strip of molar solutions in my preliminary work than I did in my plan because I wanted to look at a wider range of molar solutions and how they affect the potato cylinders. This way I can see how much of a bigger difference it makes to use the different kinds of molar solutions in my experiment. In my preliminary I used 0, 0.5 and 1 molar solutions and in my plan I used 0.2, 0.4, 0.6, 0.8, and 1 molar solution.
Method:
. First I used the potato borer to cut out eighteen potato cylinders from two whole potatoes. After pushing the potato borer through the potato, I removed the cylinders from the potato borer by poking a glass rod through it, which gently pushed the potato cylinder out from the bottom of the borer.
2. Then I cut all eighteen potato cylinders to the exact same length with a scalpel, using a ruler to measure the length. This all came to 5cm long.
3. After performing the length of the potato cylinders, I performed the mass of them on a weighing scale. Getting them to weigh around the same gram, as close as possible. They were all around 4grams.
4. I then added the appropriate amounts of volumes into the test tubes.
* 0M - 10cm³ of water
* 0.2M - 8cm³ of water and 2cm³ of sucrose solution
* 0.4M - 6cm³ of water and 4cm³ of sucrose solution
* 0.6M - 4cm³ of water and 6cm³ of sucrose solution
* 0.8M - 2cm³ of water and 8cm³ of sucrose solution
* 1M - 10cm³ of sucrose solution
Each test tube had a maximum molar solution of 10cm³. There were
three test tubes of the same molar solution. There were six molar
solutions, making eighteen test tubes altogether. Each test tube had
one potato cylinder in it.
5. After adding the solutions shown above to the eighteen test tubes by
using the squeezy bottle to put water in and a pipette for collecting the
sucrose solution from the beaker, measuring these in a measuring
cylinder to get the right amount of volumes.
Also labelling each molar solution on the test tubes with a permanent
marker so that I knew which was which, I added one potato cylinder to
each test tube. Making sure that each one was fully covered in each
solution. I tried to put all three potato cylinders in at the same time. So it
would be fairer if all of them started osmosis at the same time.
6. Next, I covered each boiling tube with a cling film, so that nothing
would affect my experiment of osmosis. Also nothing would evaporate
from the potato causing the concentration to increase.
7. I then left these eighteen test tubes on two test tube racks with my name
on it, for a couple of hours until osmosis had occurred in the potatoes.
From 11:20 till 13:30.
Equipment
How and why was it used?
Two potatoes
I used two potatoes because one potato was not enough for eighteen potato cylinders.
One potato borer
(1cm in diameter)
I used this by pushing it through the potato, which cut out thin cylinders from the potato very easily.
Scalpel
A small, safe knife to cut small amounts off the potato cylinders. So that all the cylinders were of equal length.
Glass rod
Used for removing the potato cylinder from the potato borer, pushing it gently out from the bottom, without breaking it.
Test tubes (x18)
Eighteen test tubes to hold one potato cylinder in each one for six different molar solutions.
Squeezy Bottle
A bottle full of water with a tube coming out from the top. When pressed, it squirts water into the measuring cylinder to the amount of volume needed.
Beaker (x3)
Used to contain the sucrose solution so that it was easier for me to collect some with my pipette.
One Marker Pen
For writing our names on the test tube rack and writing the amounts of molar solution on each test tube.
Pipette
Used for putting and taking out the right amount of sucrose solution needed, in each boiling tube.
Test Tube Rack (x2)
To hold all eighteen test tubes with a potato cylinder and molar solution in each one.
Ruler
To measure the length of each potato cylinder when making sure they were all the same length.
Stop clock
To time how long the experiment took and note what time I started and finished.
Measuring Cylinder
Used to get accurate volumes of water and sucrose solutions so that the amount of solution in each boiling tube would be the same.
Scales
This also has a Petri dish on it to weigh the potato cylinders.
White Tile
For when I was using the potato borer to cut out cylinders, so that I wouldn't cut myself.
Clingfilm
To wrap my boiling tubes with, after I've put the potato and the right solutions in.
Apparatus:
Osmosis is the diffusion of water molecules from a high to a low concentration, therefore water molecules from inside the potato cylinder will move out into the solution. Leaving the cytoplasm inside the cells to shrink and become flaccid. As the cells of the potato cylinder lose water they then weigh lower than they did before. They also become shorter than they were before.
In other words, when a potato cylinder is placed in a solution that has a higher concentration than the cylinder itself, the potato cylinder will lose weight (0.4, 0.6, 0.8 and 1.0 molars), because there is higher concentration of water molecules inside the potato compared to the ones outside the potato. In the same way when the potato cylinder is placed in a solution that has a lower concentration than itself, the potato cylinder will gain weight (0.0 and 0.2 molars), because there is a lower concentration of water molecules inside the potato cylinder compared to the water molecules outside the potato cylinder.
This picture is from Google images uk.encarta.msn.com/, describing the movement of water and sucrose molecules in osmosis.
Anil Vaghela 10SAC
