Required Practicals

Question 1

RP1 - List the three variations

Answer 1

Amylase:

• Hydrolyse starch to maltose
• Test using iodine in potassium iodide solution
• End -point is when blue/black colour no longer appears

Catalase:

• Catalyse the breakdown of hydrogen peroxide into water and oxygen
• Collect the oxygen produced of time to calculate the rate

Protease (e.g trypsin):

• Hydrolyse insoluble proteins into small, soluble peptides
• Measure the time taken for a cloudy protein solution to clear

Question 2

RP1 - List the factors that affect the rate of enzyme controlled reaction

Answer 2

• Enzyme conc
• Substrate conc
• Conc of competitive and non-competitive inhibitors
• pH
• Temperature

Question 3

RP2 - Overall method for preparing and observing a root tip squash

Answer 3

1. Prepare a slide
2. Use an optical microscope
3. Calculate a mitotic index

Question 4

RP2 - Give the equation for mitotic index

Answer 4

no. of cells undergoing mitosis/total no. of cells

Question 5

RP2 - Method for preparing root tip squash slide

Answer 5

1. Stand bulb in a beaker of water for 2-5 days until roots are visible
2. Cut 1 mm off the end of the root using a scalpel
3. Fixing:
   - Place the tissue in ethanoic alcohol and concentrated HCl
   - This stops cell division and hydrolyses the middle lamella so the cells can be separated easily
4. Staining:
   - Place root tip on slide and add a stain
   - e.g Toluidine blue (blue) or Acetic orcein (purple/red)
5. Preparing:
   - Squash root tip by placing cover slip on top and pressing down gently but firmly
   - This produces a single layer of cells to easily see under the microscope
   - Do not break the cover slip or move it around and damage the chromosomes

Question 6

RP2 - Method for using an optical microscope

Answer 6

• Place on stable surface in well lit area
• Turn on light
• Select the right objective lens
• Place your slide on the stage and gently slide under the clips
• Focus using course focus followed by fine focus

Question 7

RP3 - Overall method for using a calibration curve to estimate water potential

Answer 7

1. Prepare a dilution series

2. Determine the water potential

Question 8

RP3 - Method for producing a dilution series

Answer 8

• Calculate the volume of stock solution
  (Required conc/conc of stock solution) x final volume required
• Calculate the volume of distilled water to add

Do this multiple times to produce different concentrations

Question 9

RP3 - Method for determining the water potential of plant tissue

Answer 9

• Use a cork borer to produce potato cylinders
• Cut the cylinders to the same appropriate length
• Use a mass balance to record the weight of the cylinders and then place directly into the required concentrations and start the stopwatch
• Leave for five minutes
• Gently blot each cylinder dry and re-weigh

Question 10

RP3 - Percentage change equation

Answer 10

(difference/original) x 100