Practical B5

Investigate the process of osmosis by measuring the change in length or mass of plant tissue

Procedure

  1. Set up 5 labelled beakers, each containing a different concentration of sucrose.
  2. Using a cork borer cut five potato cylinders of equal length and width.
  3. Weigh/measure the length of each potato cylinder.
  4. Add 1 potato cylinder to each beaker.
  5. Leave the beakers for 1 hour.
  6. Pat the potato cylinders dry to remove excess water.
  7. Reweigh/measure the length of each potato cylinder.
  8. Record the results in a table.
  9. Calculate the change in mass/length of each cylinder.
  10. Calculate the % change in mass/length of each cylinder – as all starting measurements may not have been the same.
  11. Draw a graph of % change in mass/length against the different concentrations of sucrose.
  12. Draw a line of best fit on the graph.

The percentage change in mass/length is calculated using the following equation:

\% {change} = \frac{change}{initial} {x} {100}

Results

The potato cylinders placed in pure water or weak sucrose solutions will gain mass/length as water will have moved from an area of high concentration (outside the potato cells) to an area of lower concentration (inside the potato cells).

The potato cylinders placed in strong sucrose solutions will lose mass/length as water will have moved from an area of high concentration (inside the potato cells) to an area of lower concentration (outside the potato cells).

The sucrose concentration that causes no change in mass/length is the concentration that is equal to the potato cell.

Practical B5

Investigating the process of osmosis by measuring the change in length or mass of model cells, using Visking tubing.

Procedure

  • Add sucrose solution to a section of Visking tubing – a selectively permeable substance used to model a cell membrane.
  • Weigh the Visking tubing and its contents.
  • Add the Visking tubing to a beaker of water.
  • Leave for 1 hour.
  • Pat the Visking tubing dry to remove excess water.
  • Reweigh the Visking tubing and its contents.

Results

The Visking tubing will gain mass as water will have moved from an area of high concentration (outside) to an area of lower concentration (inside).