Osmosis is the diffusion of water across a partially permeable membrane from a dilute solution to one of a higher concentration.
If a solution has a low concentration then the amount of (in the case of my investigation) sugar, the solute, will be low and the solution will be weak. If there is high amount of sugar then the solution will be concentrated (have a high concentration).
When two solutions are divided by a partially permeable membrane; water will move from the area where there is a high concentration of water to where there is low until both sides are equal. This is known as reaching equilibrium.
A cell is turgid when it swells to its maximum volume due to large water content. Opposite to this is plasmolysis (or flaccid) where there is not enough water in the cell and the cell membrane begins to contract.
Image courtesy of the BBC website.
Factors which affect osmosis:
The difference in concentration affects the speed ay which osmosis takes place - the greater the difference in concentrations, the faster the water molecules will diffuse. External Pressure- osmosis is slowed down if there is external pressure acting against the flow of water molecules. This is due to the fact that will need more energy in order to overcome the force of pressure so they can pass through the partially permeable membrane to the other side. Size of solute molecules- if the solute molecules are large then they will block the partially permeable membrane. Water molecules will not pass through where the membrane is blocked; slowing osmosis down because fewer water molecules will be able to pass through. Temperature- an increase in temperature gives water molecules more kinetic energy which causes them to move faster meaning they also diffuse faster. However, the temperatures need to be controlled because high temperatures destroy living partially permeable membranes.
The aim of this investigation is to study how the concentration of sucrose solution affects the rate of osmosis in potato cells. The mass change of the cells will be observed when they are placed in solutions with different sucrose concentrations. The results will show how the difference in concentration on both sides of the permeable membrane.
I predict that the pieces of potato placed in sucrose solution with a concentration of 0-0.4 m/l will increase the weight of the potato and the cells will become turgid, most likely when the concentration is 0. This is because as it states in my research, the concentration of the sucrose determines how much water will transfer across the permeable membrane. When the potato pieces are placed in the sucrose solution with a concentration of 0.0-1.0, will decrease in weight as the water from the potato cells will transfer across the membrane into the solution where the concentration is higher then the cells. The cells in these potatoes, according to my research are likely to become flaccid. I also predict that there won't be a large change of weight in pieces placed in the solutions with concentrations of 0.4 and 0.6. This is because the difference in concentration in the water and potato will not be great. I predict my results graph will look like:
150ml of each of the following concentrations of sucrose solution: 0.0m/l
0.0m/l will be distilled water.
(m/l= moles/litre) (342g of sucrose in 1 litre)
*The concentration is the independent variable in this investigation as it changes so that osmosis can be measured.
1.Cut 5 tubes of potato using a 13mm borer. Cut all tubes of potato to exactly 25mm. make sure that the tubes are of a similar surface area, discard any that were on oblique cuts as this affects...