As you can see from my preliminary results, I should investigate between 0M sucrose and 0.5M sucrose as a suitable range.
I predicted that the isotonic concentration lies between 0.35M and 0.4M.
Method: I will cut 5 chips with no skin on them and have them approximately the same length, width, breadth and mass (using the balance and Vernier callipers for extra accuracy), then I will dry off the sap completely. I will use the measuring cylinder to accurately make: 20cm3 0.1M sucrose, 20cm3 0.2M sucrose, 20cm3 0.3M sucrose, 20cm3 0.4M sucrose and 20cm3 0.5M sucrose, each putting it into a boiling tube. I will then place the 5 identical chips in each boiling tube and leave for 3 hours so osmosis can occur fully.
Scientific Knowledge: A potato’s cell has a fully permeable cell wall, but a selectively permeable cell membrane, which allows certain substances to enter and not enter the cell, such as water and sucrose in this instance. In all things, everything moves from high concentration areas to low concentration areas, when in water, this process is called ‘Osmosis’. With potato (plant) cells, it swells up as water enters via osmosis, however, it won’t burst because the cell wall is tough, and it only stretches out slightly. When it can’t stretch anymore, it is called ‘Tugor’; this is what makes the plant firm and stand up. The opposite, when the cell membrane shrinks to its limit because of lack of water, is called ‘Plasmolysis’, which makes the plant wilt.
Obtaining
I have made sure my results are fully accurate and I don’t see any unusual results or anomalies. I mention ‘Safety’ and ‘Apparatus’ in the Planning section, so I don’t have to repeat myself.
Analysis
I did 0.35M just to round to the nearest 0.1M, so the concentration that is isotonic to potato cell sap is approximately between 0.3M and 0.35M sucrose solution. I didn’t put the line of beat fit on as it is an average and we don’t want an average in this case. SEE GRAPH. The computer did not draw the right scale when it came to 0.35M to I drew it on in pencil and showed what concentration the line crosses at.
Evaluation
My prediction was very close and probably was out by a tad because results can’t be perfect. I think the 0.4M result was a bit extreme and might actually lie nearer to 0 than it does. This might be due to it not being fully submerged, left in the solution for a different length of time, the chip might have been slightly different to the others in size, mass or even density. It could be because I didn’t dry it enough when I went to measure them after the 3 hours, which I think, is the most plausible one. A part from that, most or all my results were very accurate.
I would probably spent more time getting more results than the few I had, and investigated further into the exact concentration that is isotonic to potato cells, which I figure is now between 0.3M and 0.35M sucrose (aq).
If I had repeated each concentration about 3 times, I could average them and get a more reliable graph and table of results to base my conclusion on.
The potato has approximately have a 0.325M concentration of sucrose in its cells, if I were to put a potato chip in 0.325M solution of sucrose, its size and mass should not change if my results are correct. If both have the same concentration of sucrose, osmosis won’t occur, as nothing is higher or lower in concentration.
