GCSE Biology Core Practicals | Quizlet

1.10 pH Enzyme Practical - what is the aim of this prac?

To investigate how changing the pH affects the rate of starch breakdown by amylase.

What is the method? - 1.10

1. Place a drop of iodine solution into each well of a spotting tile.

2. Label test tube and add 2cm^3 of amylase solution.

3. Add 2cm^3 of a buffer solution with a known pH (e.g 5).

4. Add 2cm^3 of starch solution to the tube and start the timer immediately.

5. Every 30 seconds, use a pipette to remove a drop of the mixture and add it to the iodine on the spotting tile.

6. Continue sampling every 30 seconds until the iodine stays orange showing all starch has been digested, recording the time taken for this to happen.

7. Repeat experiment using different pH buffer solutions, e.g 4,6,7,8.

What are the variables? - 1.10

Independent: pH of the solution.

Dependent: Time taken for starch to be fully broken down.

Control: - Concentration & volume of starch, amylase, and buffer solution - temperature - sampling intervals - .

What does the experiment show / prove? - 1.10

Enzymes like amylase work best at an optimum pH, (usually around pH 7), and that too low or too high pH denatures the enzyme, changing its active site so it no longer functions.

1.16 Potato Osmosis - what is the aim of this prac?

To investigate how different concentrations of sugar solution affect osmosis in potato cells.

What is the method? - 1.16

1. Cut several equal-sized potato cylinders.

2. Measure and record the mass of each one using a balance.

3. Prepare a set of test tubes, each containing a different concentration off sugar solution, (e.g 0.0, 0.2, 0.04 mol/dm^3 etc).

4. Place one into each solution.

5. Leave them in the solution for at least 30 minutes.

6. Remove the potato cylinders and blot them gently dry with paper towel.

7. Re-measure and record their final mass and calculate the percentage change in mass for each cylinder - Percentage change = (Final mass - Initial Mass) divided by Initial Mass all * 100.

What are the variables? - 1.16

Independent: Sugar solution concentration.

Dependent: Change in mass of the potato.

Control: Volume of solution, time left in solution, size of potato cylinders, temperature.

What does it show? - 1.16

In a dilute solution which has higher water potential than the potato, water moves into the potato by osmosis, increasing the mass.

In a concentrated solution which has lower water potential than the potato, water moves out of the potato by osmosis, so the mass decreases.

When there is no change in mass, the solution is isotonic to the potato - the water potential is equal and there is no net movement of water.