required practicals

Question 1

effect of pH on enzyme action

Answer 1

On a tile, label each well with the time (from 0 onwards) and add a drop of iodine solution to each well.
2. Add 2 cm​ of each buffer solution using a syringe (ranging from pH 3.0 to 7.0) into each
labelled test tube.
3. Immerse the starch solution, amylase solution, and the test tubes of buffer solution in a water bath at 25​°C.
4. Allow a few minutes for the temperature to equilibrate.
5. Use a syringe to add 2 cm​ of amylase and 2 cm​ of starch into the into a test tube of buffer solution and start timing immediately.
7. Use the glass rod to transfer a drop of the mixture to the well labelled ‘0’ on the tile.
8. Repeat step 6 every 30 seconds, rinsing the glass rod in between every test, until the iodine
solution remains brown and does not turn blue-black.
9. Calculate the rate of enzyme reaction by using 1/ time taken for iodine solution to remain
brown.
10. Repeat steps 2-8 for buffer solutions with different pH values.
11. Plot a graph of the rate of enzyme reaction against pH.

Question 2

osmosis in potatoes

Answer 2

1. Use a cork borer to cut 5 potato cylinders.
2. Trim the cylinders using a sharp knife and a ruler to the same length (about 3 cm).
3. Accurately measure and record the length and mass of each cylinder.
4. Measure 10 cm3 of the 1.0M sugar solution and transfer to the first boiling tube and label.
5. Repeat step 4 for other concentrations of the solution and distilled water.
6. Add **one potato cylinder **(of known mass and length) to each boiling tube.
7. Leave the cylinders in the boiling tubes overnight in a test tube rack.
8. Remove the cylinders from the boiling tubes and carefully blot them dry with paper towels.
9. Measure the length and mass of each cylinder and record your measurements in the table.
   Calculate the percentage changes for each cylinder.
10. Plot a graph of change in mass (in g) against the concentration of sugar solution.
11. Plot a graph of change in length (in mm) against the concentration of sugar solution.

Question 3

microscopy

Answer 3

Peel off an epidermal layer on the onion using forceps.
2. Mount onto the microscope slide with a drop of water using a pipette, making sure the
tissue lies flat.
3. Add 2 drops of iodine solution to stain the cells.
4. Place the cover slip on by first placing one edge down on the slide and slowly lowering the other side of the cover slip using forceps. Make sure no air bubbles are trapped.
5. Remove any excess stain by soaking it with paper towels.
6. Place the slide on the stage of the microscope.
7. Turn the nosepiece to select a low power objective.
8. use the coarse adjustment knob to raise the stage until the cover slip just touches the objective.
9. Now look into the eyepiece and turn the coarse adjustment knob to move the stage away
until the image comes into focus (doing this helps avoid you breaking the slide).
10. Turn the nosepiece to select a high power objective.
11. Repeat the same process as above and then look into the eyepiece and turn the fine adjustment knob until the image comes into focus.
12. Make a labelled drawing of a few of the cells you can see, including any features eg. cell wall, nucleus. Write down the magnification.
13. Repeat these steps using a prepared slide