Osmosis in Action – An Investigation Exercise

The process of osmosis causes water to pass into, and out of, living cells. This occurs because:

·  cell membranes are semi-permeable

·  cytoplasm consists of about 90% water, but the remaining 10% is made up of large molecules (e.g. sugars and proteins) that cannot pass through the membrane by diffusion.

Water will diffuse into a cell when the water concentration is higher outside the cell (for example, a cell in water). This causes the cell to swell up and become turgid.

Water will diffuse out of a cell if the water concentration inside the cell is higher than it is outside (for example, a cell in a strong salt solution). This will cause animal cells to become flaccid and plant cells to plasmolyse.

Your Task:

Below are the mixed up results of an osmosis investigation using carrot lengths and various concentrations of sugar solution.

  1. Match together the information below (solution concentration, final length of carrot and diagram of what the carrot cell will look like) using your knowledge of the effect of osmosis on cells
  2. Answer the questions using what you know about osmosis and cell structure
  3. Complete the “Osmosis in Action” Graphic Organiser
  4. Graph the results (i.e. change in length of carrot (y-axis), concentration of solution (x-axis))
  5. Explain the results in terms of osmosis

Results after 24 hours:

Average Carrot Length (original length = 4cm)

Sugar Solution Concentration

Cell Diagram

I II III IV

Questions

  1. What was measured as a result? ______
  2. Why is it important to start with at least a 4cm length of carrot? ______
  3. How else can you ensure accuracy of measurement? ______
  4. In this example we can only see the length of the carrot; what is a suitable “design” shape for the pieces of carrot to give the most reliable results? ______
  5. Explain the value of having 3 repeats for each solution (Hint: look at the word under “Results”) ______
  6. What supporting observations might you be able to make? ______
  7. Why is it important that the carrots were left overnight in the solutions? ______