GCSE: Science (Double Award): Biology: CCEA: Investigating osmosis (prescribed practical)

Investigating osmosis (prescribed practical B5) potato in different solutions

Aim: to investigate osmosis by measuring the change in mass of plant tissue in solutions of different concentrations

Method for B5: Potato n different solutions

Method

1. Cut a length of potato using a cork borer

2. Cut 5, 2cm pieces of potato using a scalpel and ruler.

3. Use a measuring cylinder to measure 10ml of distilled water into a test tube. Repeat for 5%, 10%, 15% and 20% sucrose solutions.

4. Record the initial mass of each potato cylinder using a mass balance.

5. Place one potato cylinder in each test tube.

6. Leave for 40 minutes.

7. Remove each potato cylinder, gently dry with a paper towel and record the final mass of each cylinder

8. Calculate the change in mass of the potato for each solution and display the results as a line graph.

Risk assessment

Cork borer- cut skin, solution: cut on a tile

Glassware- broken glass, solution: keep beakers in the centre of the table

Variables

Independent- concentration of sucrose solution

Dependent- mass of potato

Control- size of potato, time left in solution, volume of solution

Conclusion

In conclusion, the concentration of sugar inside the potato was. 8.%. At this point in the

graph there is no movement of water by osmosis.

Above this concentration, water moved out the potato by osmosis and below this

concentration water moved into the potato by osmosis.

In pure water explanation:

Higher concentration of water in the solution

Water moves into the potato

Potato gained mass

Potato cells are turgid

Same concentration as potato explanation:

Equal concentration

No net movement of water

Potato mass is constant

In concentrated salt/ sugar solution explanation:

Higher concentration of water in potato

Water moves out of potato

Potato loses mass

Potato cells are are plasmolysed

Where does the water move?

Water moves to where there is less water: wants to get a balance (No net movement)

Investigating osmosis using visking tubing (prescribed practical B5)

Visken tubing a selectively permeable similar to a cell membrane. It can therefore be used to model the movement of substances into and out of a cell.

Method (visking tubing)

Method:

1. Measure 100ml of distilled water into a 250ml beaker and label it distilled water.

2. Repeat with each of the 3 known sucrose solutions.

3. Cut 4 x 20cm lengths of Visking tubing. Tightly tie one end of each.

4. Add the unknown sucrose solution (X) to the 4 Visking tubes using a fresh dropper until the filled portion is about 6cm long and securely tie the ends.

5. Cut off any excess visking tubing

6. Use the balance to record the initial mass of each visking tubing then place it into the correct solution for an hour

7. Remove the visking tubing, dry it gently with a paper towel

8. Use the balance to re weigh each of the visking tubes. Record results.

Conclusion for visking tubing experiment

The concentration of the unknown solution inside of the visking tubing was 7.5%. At this point on the graph. The percentage change in mass is zero, there is no movement of water by osmosis.

Visking tubing experiment results

If there is a higher concentration of water in the solution. (Dilute)

Water moves into the visking tubing

Visking tubing gains mass and is turgid

If there is a higher concentration of water in visking tubing (solution is concentrated)

Water moves out of the visking tubing

Visking tubing loses mass and is plasmolysed