In this I will be investigating what effects the movement of water through osmosis. Osmosis is the diffusion of water. It is the process in which fluids pass through a partially-permeable membrane. It is the movement of water from high water concentration to low water concentration. Plant cells react to osmosis by hypertonic, isotonic and hypotonic.
Hypertonic – is when the water outside of the cell is lower than that inside. Isotonic – is when the net movement is the same in both directions. Hypotonic – is when the water potential outside the cell is higher. Therefore the water has moved into the cell and the cytoplasm is pushing against the cell wall and the cell has become turgid.
(Pictures from http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_21c/life_processes/plantfoodrev3.shtml)
Water Potential is when the water molecules in a system have a tendency to move from one place to another, it is usually represented by the Greek letter Ψ (Psi). Water potential is caused by osmosis.
Water potential (Ψ) is calculated by using the following equation: Pressure potential (Ψp) + Solute potential (Ψs)
Factors that affect the movement of water
* Concentration – As the water molecules will move from a high concentration of water to a low concentration of water. * Temperature – The hotter the temperature is the faster osmosis will take place as the particles will move more.
Chosen Factor – Sugar Concentration
In this investigation, I will be monitoring the effect sugar concentration has on the movement of water.
My hypothesis is: By changing the concentration of sugar, I think that the water will move from a high water concentration to a low concentration via osmosis. I predict that the more sugar concentration there is, the rate of osmosis will increase and therefore will have an effect on the results of the experiment.
I found three different methods I could use to measure the rate of osmosis: * Observing osmosis using a model cell  – With this one I will be using an artificial membrane to act as a cell membrane. For this I will use visking tubes. * Observing osmosis using potato cylinders and measuring the gain or loss of mass  – For this one you use bits of potato in different sucrose solutions. * Observing osmosis using aubergine chips and measuring the gain or loss of length - This one is similar to the potato one but with aubergine instead.
Easy to do| The visking tubes are fiddly|
Don’t need to keep an eye on it| The visking tubes are easy to break| Quick process| Might have leaks in the visking tubes|
Easy to get hold of the equipment| |
Don’t have to keep an eye on the experiment| Hard to cut the aubergine to exactly 1cm³ cubes| You can tell by the colour of them what has happened to them in the solutions| The aubergine goes brown really quickly as bacteria is getting to it.| Equipment is easy to use and to get hold of| Aubergine is easy to break| Safe to use the equipment, other than the scalpel | Long to do |
All the potato cylinders are the same width and length | Long process to do| Easy to do | The potato cylinders are easy to break|
Easy to cut them to sensible length| Hard to get out of the corer| Easy to use the equipment, apart from the corer.| Difficult to get a certain number of potato cylinders from one potato|
I’ve decided to use the potato cylinder method to observe the rate of osmosis.
Observing osmosis using a model cell does not give very reliable results as the visking tubes might have leaks in them. It is also a very fiddly job to open the visking tubes, to pour the solution in.
Observing osmosis by using aubergine chips is tough one to do, as you have to cut the aubergine chips to exactly...