REQUIRED PRACTICALS PAPER 1

Question 1

Describe how to carry out required practical 1 (investigating the effect of a named variable on the rate of an enzyme controlled reaction)

Answer 1

• place four test tubes in a test tube rack
• draw a cross on two of the test tubes in the middle
• place 10cm3 of milk in the 2 test tubes with cross
• place 4cm3 of pH7 buffer solution in one of the empty test tubes (control group)
• place 2cm3 of pH7 buffer solution in the other empty tube along with 2cm3 0.5% trypsin
• place all test tubes in water bath at chosen temperature
• once all test tubes have reached chosen temperature, mix the control test tube with the milk and the trypsin test tube with the other tube of milk
• place back in the water bath and set a timer
• watch the test tubes and when you can see the cross through the trypsin test tube, stop the timer
• repeat with 5 other temperatures
• plot graph

Question 2

Describe how to carry out required practical 4 (investigating cell membrane permeability)

Answer 2

• gather 5 test tubes and fill them with 20cm3 of water
• place one in ice cold water and the rest in water baths of different temperatures: 20,40,60,80
• use cork borer to get 5 evenly sized cylinders of beetroot, cut them to the same size using a ruler
• place in water to get rid of excess pigment and then towel dry
• place each cylinder into a separate test tube of different temperatures
• leave for 5 mins
• place some liquid from each test tube into its own cuvette
• place them one by one in a colorimeter with blue light
• record absorbance
• plot graph

Question 3

Describe how to carry out required practical 2 (calculating mitotic index using plant cells)

Answer 3

• heat 1 mole dm3 HCL in a water bath at 60degrees for 10 minutes
• remove the tips from the root of garlic (around 1cm)
• place in the warmed HCL for 5mins)
• rinse the tips well with cold water and blot dry
• cut 2mm of the tip and place onto slide
• use 2 mounted needles to tease the root apart
• place a drop of 1% toluidine blue on tip and leave for 1-2 mins
• place cover slip on slide, squash down gently
• place under microscope and observe
• calculate mitotic index:
  Number of cells with visible chromosomes/total number of cells in sample

Question 4

Describe how to carry out required practical 6 (use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth)

Answer 4

1. Use antiseptic cleaner to disinfect working station, run neck of broth bottle through Bunsen burner to disinfect
2. Use a sterile pipette to transfer bacteria from broth to agar plate
3. Open Petri dish slightly and dispense broth onto agar plate
4. Run spreader through flame and then use to spread broth evenly over agar plate
5. Use forceps to place a multi disc antibiotic ring on the plate
6. Lightly tape lid on, invert and incubate at 25degrees for 48hours
   - sterilise all equipment and disinfect surfaces
   After incubation:
   Measure the diameter of the inhibition zone for each antibiotic, without removing lid
   Work out the area of inhibition zone using the formula:
   A = pi x diameter2/4

Question 5

Describe how to carry out required practical 3 (investigating water potential)

Answer 5

1. Make a dilution series of 1M salt solution and label boiling tubes 0, 0.2, 0.4, 0.6, 0.8, 1.0 mol/dm3
2. Add distilled water to each boiling tube making them 20cm3
3. Use a cork borer to cut 6 identical cylinders of potato, cut them to the same length using a ruler
4. Pat them dry to remove any excess moisture
5. Measure the before mass of each cylinder and record masses in a table
6. Place a cylinder in each solution
7. After 1 hour, remove the cylinders from solution and blot dry
8. Measure after mass and then calculate the change in mass