The independent variable in this experiment is the thing that I will be changing in the experiment. This is the range of concentrations that have been obtained by diluting the original 1M solution of Sucrose. This is therefore the only thing that is going to be altered as I am investigating how different percentage of water molecules affects the weight of the the potato thus the rate and direction of osmosis.
The dependant variable will be the mass of the potato as this is the variable I will be measuring. From this I can see the change in mass(g) and so work out the amount of water that has moved and the rate of the osmosis in a set time. This can then be used to see how the concentration affects osmosis. I
The control variables are the set of factors that must be kept the same for every test to make sure that the results are reliable. The first controlled variable is the type of potato. This is because it may have more or less water than another type as well as a different selective membrane and so the results may be altered because of this. If the potato has more water, for example, the weight of the potato might go up with one type whilst go down with another even if it was in the same solution; therefore the potato type must be controlled throughout the tests.
The second control variable is the mass of the potato and the surface area. This may affect the results because if the potato is bigger and so the surface area is greater it will mean the membrane on the outside is bigger an so more areas for the osmosis to occur. Because of this I will be using a cork borer to make the cylinder sample the same size throughout the experiment and then cut them to the nearest millimetre. Also all samples will be weighed and it will be the difference in mass that is observed as it may be a few hundredths of a gram out, every time, due to