Osmosis in potato tissue
Soak potato cylinders in sucrose solutions, measure the change in mass and find the concentration of the cell sap.
Objectives
- Measure the change in mass of plant tissue in solutions of different concentration.
- Explain the results in terms of osmosis.
- Estimate the concentration at which there is no net movement of water.
Theory
Osmosis is the net movement of water through a partially permeable membrane from a dilute solution to a more concentrated one. In a dilute solution potato cells take in water and the tissue gains mass. In a concentrated solution they lose water and the tissue loses mass. Where the line of percentage change against concentration crosses zero, the solution has the same water potential as the cell sap: it is isotonic. Percentage change = (final mass − initial mass) ÷ initial mass × 100. Using a percentage allows cylinders of slightly different mass to be compared.
% change = (m₂ − m₁) ÷ m₁ × 100
Procedure
- Weigh a cylinder, soak it in distilled water (0 mol/L) and weigh it again.
- Repeat for five or more different sucrose concentrations.
- Plot percentage change in mass against concentration and find where the line crosses zero.
Precautions
- Blot each cylinder the same way before weighing.
- Cut all cylinders to the same length and remove the skin.
- Leave them for the same time.
- Subject
- Biology
- Grade
- 9–11
- Chapter
- Cell and Transport (Nepal National Curriculum (CDC), grade 10)
- Difficulty
- Medium
- Duration
- 25 min
- Safety level
- Low
- Version
- 1.0
Apparatus
- Potato
- Cork borer
- Sucrose solutions
- Boiling tubes
- Balance (0.01 g)
- Paper towel
- Ruler
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