Another term is flaccid, which is the state of the plant cell when it has lost water so that it stops pushing out against the cell wall. The cytoplasm and the vacuole shrink, then the plant loses its firmness and begins to wilt. However, when the plant cell reaches the extremity of water loss through osmosis then it is said to be plasmolysed. This happens when the plant cell is in a very concentrated solution and the water has diffused out of the cell causing the cytoplasm and the vacuole to shrink even further. The cell membrane tears away from the cell wall, and on this the membrane becomes damaged and the cell dies. Plant cells do not normally become plasmolysed naturally because they are never usually in such strong solutions but they can be plasmolysed with intervention
The aim of the investigation is to explore osmosis in potatoes and find its sucrose concentration. With regard to the osmosis, it will be taking place across cell membranes in the potato. The cells in the potato will be similar to the plant cells explained previously in terms of how osmosis occurs. Therefore I predict that water will diffuse into the potato if it is put into pure water. Also I expect water to diffuse out of the potato if it is put into a very concentrated sucrose solution. This is because there must be a considerable amount of water in the potato cells already seeing as a potato is a root vegetable and absorbs water into the ground.
The sucrose concentration of the potato will be found when the potato is put into a concentration of solution in which no osmosis or diffusion of water takes place. From my own general knowledge I know that the water content of potatoes is approximately 70%. This is a notorious quantity of water found in nature e.g. the composition of humans is 70% water, the composition of the Earth is 70% water etc. So from this information I can predict that osmosis will not take place in a solution that is approx. 70% water and the sucrose concentration in the potato will be approx. 30%.
In connection with the pattern of osmosis at different solution concentrations, I think that if the potato is put into pure water then xcm3 of water will diffuse into the potato, and if the potato is put into a concentration half way between that of itself and pure water then 0.5xcm3 of water will diffuse into the potato. If the potato is put into a concentrated sucrose solution then ycm3 of water will diffuse out of the potato, and if the potato is put into a concentration half way between that of itself and the concentrated sucrose solution then 0.5ycm3 of water will diffuse out of the potato.
Method:
Use the hole-borer to cut out 12 cylinders from the two potatoes making sure that all the cylinders are at least 5cm long. Then using the ruler and knife, crop all the cylinders down to exactly 5cm in length on the tile. Keep the 12 cylinders aside. Now you have to make up six different concentrations of sucrose solution using the 1.0M solution provided and diluting it with water. To make the concentrations I used the following proportions:
I made the solutions by using pipettes to measure the sucrose solution in one beaker and the water in a second beaker, then mixing both in a third beaker with a stirrer. With another pipette I put 10ml of each concentration into two test tubes so that there were two tubes with 0.2M, two tubes with 0.24M etc. I measured the mass of the potato cylinders and recorded the values, before putting the cylinders into the solutions, one cylinder in each test tube. I put labels on each tube to show which tube contained which concentration so that there was no error in mixing up the results.
After leaving the potatoes for 24 hours (probably sufficient time for osmosis to take place) I drained away the solutions from the tubes, took out the potato cylinders and reweighed them, recording the new values next to the previous ones.
