Coursework - Osmosis

Essay by sweeteliF, November 2004

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Coursework - Osmosis


Aim: To investigate what concentration of sucrose solution is isotonic to potato cell sap.

Apparatus:0M sucrose (aq) (distilled water)

2M sucrose (aq)


Chip cutter


Boiling tubes

Measuring cylinder (25cm3)

Vernier callipers (to nearest 0.1mm)

Balance (to nearest 0.01gram)

Safety: I will ensure safety around the lab by: wearing safety goggles, laying paper towels, removing baggage from walking space, push stools under the bench, stand up, walk carefully and slowly - don't rush and handle equipment and apparatus carefully.

Preliminary Experiment: I did a small experiment before doing the real one so I could find a suitable range to base my investigation round. I used 3 chips in 3 boiling tubes, each containing 20cm3 of: 0M sucrose, 0.5M sucrose and 1M sucrose.

Moles of Sucrose /M Original Mass /g Mass after 3 hours /g Up/Down in mass

0M 8.02 9.94 Up

0.5M 8.18 7.83 Down

1M 8.83

7.20 Down

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...