core prac 9

Question 1

independent variables for the garlic antimicrobial prac?

Answer 1

Substance whose antimicrobial properties are being tested e.g. garlic or mint

Question 2

What is the dependent variable for the antimicrobial prac?

Answer 2

Zone of inhibition made by the substance

Question 3

What are the control variables for the antimicrobial prac?

Answer 3

• same concentration of plant material used.
• type/amount of bacteria used.
• volume of plant material used for each disc.
• contamination of culture (aseptic technique should be used)
• temperature of cultures
• pH of medium

Question 4

What could the negative control be for the antimicrobial prac?

Answer 4

• Four sterile paper discs soaked in distilled water placed on a petri dish with e-coli.
• acts as a negative control to see if bacteria die regardless of plant material used.

Question 5

method of antimicrobial prac…

Answer 5

1. crush 3g of garlic with pestle & mortar and use measuring cylinder to add 10cm3 of denatured alcohol to mixture, shake the mixture occasionally for 10mins.
2. repeat step 1 but use 3g of mint as plant material.
3. pipette 0.1cm3 of garlic extract solution onto 4 sterile paper discs, allow each disc to dry. Repeat for mint extract solution.
4. label other petri dishes for garlic, mint and control solutions including the date.
5. use sterile forceps to place all 4 discs of each extract type onto corresponding petri dish, close each dish and seal with tape. Make sure a small gap is left so oxygen can enter and there’s no build-up of anaerobic bacteria.
6. leave cultures to incubate overnight.
7. open each petri dish and use a ruler to work out zone of inhibition for each disc.