Amy Grammer 11.6
AT1
Aim: - To investigate the effect of varying concentration of a certain sugar solution on the amount of osmotic activity between the solution and the potato chip.
Background information
If a dilute solution is separated from a concentrated solution by a partially permeable membrane, water diffuses across the membrane from the dilute to the concentrated solution. This is known as Osmosis.
A partially permeable membrane is porous but allows water to pass through more rapidly than dissolved substances. Since a dilute solution contains, in effect, more water molecules than a concentrated solution, there is a diffusion gradient that favours the passage of water from the dilute to the concentrated solution.
In living cells, the cell membrane is partially permeable and the cytoplasm and vacuole (in plant cells) contain dissolved substances. As a consequence, water tends to diffuse into cells by Osmosis if they are surrounded by a weak solution, e.g. fresh water. If the cells are surrounded by a stronger solution, e.g. salt water, the cells may lose water by Osmosis.
Water Potential.
The water potential of a solution is a measure of whether it is likely to lose or gain water molecules from another solution. A dilute solution, with its high proportion of free water molecules, is said to have higher water potential than a concentrated solution, because the water will flow from the dilute to the concentrated solution (from a high potential to a low potential). Pure water has the highest possible water potential because water molecules will flow from it to any other aqueous solution, no matter how dilute.
Further information on plant cells.
Plant cells always have a strong cell wall surrounding them. When they take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant cells become turgid when they are put in dilute solutions. Turgid means swollen and hard. The pressure inside the cell rises and eventually the internal pressure inside the cell is so high that no more water can enter the cell. This liquid or hydrostatic pressure works against Osmosis. Turgidity is very important because this is what makes the green parts of the plant stand up into the sunlight.
When the plant cells are placed in concentrated sugar solutions they lose water by Osmosis and they become flaccid. This is the exact opposite of turgid. The contents of the potato cells shrinks and pulls away from the cell wall. These cells are said to be plasmolysed.
When the plant cells are placed in a solution that has exactly the same Osmotic strength as the cells they are in a state between turgidity and flaccidity. We call this incipient plasmolysis. Incipient means about to be.
Preliminary Experiment.
This experiment is very basically a mini version of my actual experiment. It will have less repeats of results and will be using a smaller variety of concentrations of sugar solutions but will help us get some idea of what to expect in practise, not just in theory. It will also help take any problems into account for my actual experiment.
Apparatus.
White tile.
Petri dishes.
Potatoes
Potato corer.
Knife.
Water.
Sugar solutions (5% and 20% sucrose).
Marker pen.
Stop clock.
Electronic scales.
Method.
. Find a good hard ripe potato and push the potato corer all the way through onto the white tile. Push the cylinder of potato through the potato corer.
2. Cut the ends off the cylinder and then cut 3 discs of potato for each petri dish (9 in total) of roughly 60mm in depth on the white tile.
3. Using the marker pen write 1. 2. And 3. On each different disc of potato.
4. Prepare to weigh the disc by drying them off with a cloth. Put 3 pieces of potato in each of the 3 petri dishes, clearly marked water, 5% and 20%.
5. Find the mass of each piece of potato using electronic scales. Note these down and use the same scales each time for accurate results.
6. Cover the potato discs in the water petri dish with water and the discs in the 5% petri dish with 5% with 5% sugar solution and likewise for the 20%.
7. Leave for 1 hour. Time it using the stop clock.
8. After 1 hour, dry off the pieces of potato and weigh them again.
Results.
Before mass (g)
After mass (g)
Mass difference (g)
Water 1.
0.95
.09
+0.14
Water 2.
0.83
0.96
+0.13
Water 3.
0.76
0.88
+0.12
5% 1.
AT1
Aim: - To investigate the effect of varying concentration of a certain sugar solution on the amount of osmotic activity between the solution and the potato chip.
Background information
If a dilute solution is separated from a concentrated solution by a partially permeable membrane, water diffuses across the membrane from the dilute to the concentrated solution. This is known as Osmosis.
A partially permeable membrane is porous but allows water to pass through more rapidly than dissolved substances. Since a dilute solution contains, in effect, more water molecules than a concentrated solution, there is a diffusion gradient that favours the passage of water from the dilute to the concentrated solution.
In living cells, the cell membrane is partially permeable and the cytoplasm and vacuole (in plant cells) contain dissolved substances. As a consequence, water tends to diffuse into cells by Osmosis if they are surrounded by a weak solution, e.g. fresh water. If the cells are surrounded by a stronger solution, e.g. salt water, the cells may lose water by Osmosis.
Water Potential.
The water potential of a solution is a measure of whether it is likely to lose or gain water molecules from another solution. A dilute solution, with its high proportion of free water molecules, is said to have higher water potential than a concentrated solution, because the water will flow from the dilute to the concentrated solution (from a high potential to a low potential). Pure water has the highest possible water potential because water molecules will flow from it to any other aqueous solution, no matter how dilute.
Further information on plant cells.
Plant cells always have a strong cell wall surrounding them. When they take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant cells become turgid when they are put in dilute solutions. Turgid means swollen and hard. The pressure inside the cell rises and eventually the internal pressure inside the cell is so high that no more water can enter the cell. This liquid or hydrostatic pressure works against Osmosis. Turgidity is very important because this is what makes the green parts of the plant stand up into the sunlight.
When the plant cells are placed in concentrated sugar solutions they lose water by Osmosis and they become flaccid. This is the exact opposite of turgid. The contents of the potato cells shrinks and pulls away from the cell wall. These cells are said to be plasmolysed.
When the plant cells are placed in a solution that has exactly the same Osmotic strength as the cells they are in a state between turgidity and flaccidity. We call this incipient plasmolysis. Incipient means about to be.
Preliminary Experiment.
This experiment is very basically a mini version of my actual experiment. It will have less repeats of results and will be using a smaller variety of concentrations of sugar solutions but will help us get some idea of what to expect in practise, not just in theory. It will also help take any problems into account for my actual experiment.
Apparatus.
White tile.
Petri dishes.
Potatoes
Potato corer.
Knife.
Water.
Sugar solutions (5% and 20% sucrose).
Marker pen.
Stop clock.
Electronic scales.
Method.
. Find a good hard ripe potato and push the potato corer all the way through onto the white tile. Push the cylinder of potato through the potato corer.
2. Cut the ends off the cylinder and then cut 3 discs of potato for each petri dish (9 in total) of roughly 60mm in depth on the white tile.
3. Using the marker pen write 1. 2. And 3. On each different disc of potato.
4. Prepare to weigh the disc by drying them off with a cloth. Put 3 pieces of potato in each of the 3 petri dishes, clearly marked water, 5% and 20%.
5. Find the mass of each piece of potato using electronic scales. Note these down and use the same scales each time for accurate results.
6. Cover the potato discs in the water petri dish with water and the discs in the 5% petri dish with 5% with 5% sugar solution and likewise for the 20%.
7. Leave for 1 hour. Time it using the stop clock.
8. After 1 hour, dry off the pieces of potato and weigh them again.
Results.
Before mass (g)
After mass (g)
Mass difference (g)
Water 1.
0.95
.09
+0.14
Water 2.
0.83
0.96
+0.13
Water 3.
0.76
0.88
+0.12
5% 1.
