Experiments

Question 1

When testing a solution for the presence of a reducing sugar, you used either Benedict’s or
Fehling’s test. A control was included.

1. Name the substance which you used as a control.
2. What colour were the contents of the control tube at the end of the test?

Answer 1

1. Water

2. Blue

Question 2

In relation to the isolation of DNA from a plant tissue, explain why you used each of the
 following:
1. Washing-up or similar liquid.
 2. Sodium chloride.
 3. Protease.
 4. Freezer-cold ethanol.

Answer 2

1. To breakdown the cell membrane
2. To cause the DNA to clump (salt)
3. To breakdown the protein in the chromosomes
4. To dehydrate and separate the DNA

Question 3

In relation to an investigation you carried out into heat denaturation of an enzyme, answer
the following:
1. Name the enzyme you used.
2. Name the enzyme’s substrate.
3. Name the product(s) formed.
4. How did you denature the enzyme?
5. How did you know that the enzyme had been denatured?
6. Why are buffers needed when carrying out experiments with enzymes in school?

Answer 3

1. Catalase
2. Hydrogen Peroxide
3. Oxygen
4. Boil
5. No foam produced in denatured enzyme, foam in other test tube-presence of oxygen
6. To keep pH constant

Question 4

Answer the questions below in relation to the growth of leaf yeast in the laboratory.

1. What principal nutrient was added to the agar for the yeast?
2. How did you introduce the yeast into the Petri dishes?
3. What did the yeast look like when it had grown on the agar?

Answer 4

1. Malt (extract)
2. Attach leaf pieces to lid
   Replace lid and store upright for 24 hours
3. Pink colonies

Question 5

Testing effect of pH on enzyme

1. How pH varied
2. How temp. kept constant
3. Enzyme name
4. Enzyme source
5. Enzyme substrate
6. Enzyme product

Answer 5

1. Buffer solutions
2. Water bath-25C and thermometer
3. Catalase
4. Celery
5. Hydrogen peroxide
6. Oxygen

Question 6

Testing effect of pH on enzyme

Describe process

Answer 6

Chop celery. 
Add buffer pH 4, washing up liquid, celery into graduated cylinder. 
Add hydrogen peroxide to boiling tube.
Place both in water bath. 
Add HP to GC and record volume. 
Wait 2 mins and record final volume.
Repeat with other pH buffer solutions

Question 7

Enzyme immobilisation

1. Enzyme name
2. Enzyme source
3. Immobilised with
4. Hardened with
5. Enzyme substrate
6. Enzyme product
7. Why dropped @ an angle
8. Control
9. How tested
10. Why beads rinsed

Answer 7

1. Sucrase
2. Yeast
3. Sodium alginate
4. Calcium chloride
5. Sucrose
6. Glucose
7. Prevent clumping
8. Yeast and water
9. Glucose testing strips
10. to remove any free yeast

Question 8

Prepare alcohol

1. What process does it involve
2. Def. of fermentation
3. Equation for experiment
4. When is fermentation complete
5. How to keep anaerobic environment
6. What is control
7. How to show CO2 is produced
8. What is used to fermintate the glucose?

Answer 8

1. Anaerobic respiration/fermentation
2. Production of a substance in the absence of oxygen
3. Glucose–yeast+no O2—> ethanol, CO2, energy
4. Stops bubbling
5. Boil glucose solution, put layer of oil on top
6. Just glucose
7. Lime water turns milky
8. Yeast

Question 9

Effect of temperature on enzymes

1. How to measure enzyme activity
2. Why is celery chopped
3. Why is buffer pH 9 used?
4. How is temperature varied

Answer 9

1. amount of foam produced
2. To expose enzyme and increase surface area
3. Optimum pH for catalase. Keep pH constant so temp only variable
4. Water baths

Question 10

Growth of leaf yeast

1. Function of agar plates
2. Aseptic techniques
3. Why leaves from countryside
4. How leaf discs cut
5. How leaf discs inserted into plates
6. Why not open dish completely
7. How leaf is held in place
8. Which side of leaf faces agar and why?
9. How is dish sealed
10. How petri dishes stored
11. Expected result
12. How to dispose of dishes

Answer 10

1. Provides nutrition for growth
2. Flame cork borer, wipe surfaces, flame forceps
3. Less pollution so more yeast
4. Cork borer
5. Forceps, lift lid slightly, insert leaves, reflame forceps each time.
6. So not to expose to other microorganisms which would affect results.
7. Petroleum jelly
8. Bottom side of yeast faces agar so yeast can drop onto it.
9. Parafilm
10. right way up (agar on bottom, leaf on top) for 1 day then upside down and incubate for 3 days.
11. Pink colonies
12. soak in Milton for 24 hrs

Question 11

Animal cell

1. How sample taken and transferred
2. Why cover slip @ 45 degrees?
3. What used to lower cover slip
4. What stain used
5. How stain applied
6. Diagram of animal cell as seen
7. Microscope use
8. function of cover slip

Answer 11

1. Innoculating loop
2. To prevent air bubbles
3. Mounted needle
4. Methylene blue stain (Me-my cheek cell)
5. Dropped with dropper onto sample
6. Just cell membrane and nucleus.
7. Low power objective lens and course focus knob first. Then High power lens and fine focus knob.
8. Protects sample