Osmosis required practical

"Investigate the effect of a range of concentrations of salt or sugar solutions on the mass of plant tissue."

In cells, different organisms, organs, and tissues have varying concentrations of dissolved substances in their cytoplasm. 

We can investigate the concentration of dissolved substances in potato tissue by using osmosis to observe how the potato’s mass changes when placed in solutions of different salt concentrations.

1. Use a scalpel to cut five potato cubes, each with the same dimensions, such as 1 cm³. Consistent size is important to ensure that each piece has the same surface area for osmosis.

2. Blot each potato cube with tissue to remove excess surface water, then weigh each one using a balance. Removing excess water ensures that the initial mass is accurate and not affected by varying water amounts on the surface.

3. Use measuring cylinders to pour 30 cm³ of five different salt solutions (at different concentrations, usually measured in moles per litre) into five separate boiling tubes.

4. Place the boiling tubes in a water bath set to 25°C and leave them for 5 minutes. This step ensures that the solutions reach the same temperature, as osmosis occurs faster at higher temperatures, which could impact results if not consistent.

5. Place one potato cube into each boiling tube with different salt concentrations.

6. Leave the potato cubes in the solutions for 20 minutes to allow osmosis to occur.

7. After 20 minutes, remove each potato cube, blot it dry, and weigh it again.

Experimental set-up

Results

Expected Results:

• Potato pieces in dilute (low concentration) salt solutions will gain mass as water moves into the cells by osmosis.

• Potato pieces in concentrated (high concentration) salt solutions will lose mass as water moves out of the cells by osmosis.

Plotting Results:

• Calculate the percentage change in mass for each potato cube using the formula: Percentage Change = (End mass - start mass) / start mass x 100

• Plot these results on a graph with percentage change in mass on the y-axis and salt solution concentration on the x-axis. By drawing a line of best fit, you can estimate the concentration of dissolved substances within the potato cells. The point at which the line crosses the x-axis (0% change in mass) indicates the concentration at which there is no net movement of water, as the inside and outside concentrations are equal.