Required Practical

Question 1

Method to investigate the effect of antiseptics or antibiotics on bacterial growth using agar plates and measuring zone inhibition:

Answer 1

1. Clean an area of desk with disinfectant
2. Remove the lid from the bacterial culture and quickly
   pass the neck of the bottle through a yellow Bunsen flame to sterilise it
3. Remove a drop of culture using the sterile pipette
4. Lift the lid of the Petri dish just enough to drop the bacteria over the surface. Quickly replace it. Put the pipette into the disinfectant.
   dipping in disinfectant and then placing in Bunsen flame.
   Then allow it to cool.
5. Spread out the bacteria to cover the surface using the spreader. Do not lift lid more than needed.
6. Put the spreader back into the disinfectant.
   Adding the antibiotics:
7. Sterilise the forceps by dipping in disinfectant and then placing
   in Bunsen flame. Then allow it to cool.

Question 2

Apparatus used to investigate the effect of antiseptics or antibiotics on bacterial growth using agar plates and measuring zone inhibition:

Answer 2

• petri dish containing agar jell
• sterile pipette
• spreader
• bacterial culture
• marker pen
• different antibiotic disks
• filter paper disk dipped in water
• stick tape
• disinfectant
• eye protection forceps

Question 3

How are microorganisms studied by scientists?

Answer 3

• microorganisms are very small, so in order for scientists to
study them they need to grow many of them in the lab using nutrients (culturing them)

Question 4

What are uncontaminated cultures of microorganisms needed for?

Answer 4

uncontaminated cultures of microorganisms are required for investigating the action of disinfectants and antibiotics

Question 5

How are microorganisms grown on agar gel plate?

Answer 5

• the agar acts as a culture medium and bacteria grown
on it form colonies on the surface
• Making the plate:
• hot sterilised agar jelly is poured into a sterilised
Petri dish, which is left to cool and set
• Wire loops called innoculating loops are dipped in a solution of the microorganism and spread over the agar

Question 6

How and when do bacteria multiply?

Answer 6

if bacteria have a supply of nutrients and a suitable temperature, bacteria can multiply quickly by binary fission as fast as every 20 mins

Question 7

If the microorganisms are bacteria what can they used be test?

Answer 7

• can be used to test the effect
different antibiotics have on their growth
• investigation involves soaking paper disks in different antibiotics which are placed on an agar plate
• after leaving the plate, the size of the clear area around the discs shows how many bacteria have died and therefore how effective the antibiotic is

Question 8

Explain the reason for there being a disk of water (in investigation of the effect of antiseptics or antibiotics on bacterial growth using agar plates and measuring zone inhibition):

Answer 8

control to see that the antibiotics are what’s killing the bacteria

Question 9

Why may a certain antibiotic may not be the best to threat a throat
infection?

Answer 9

may not be best treatment as don’t know if throat infection is a bacterial infection or if the bacteria of the
Petri dish is the same as the bacteria for her infection

Question 10

Important steps in the investigation of the effect of antiseptics or
antibiotics on bacterial growth using agar plates and measuring zone inhibition:

Answer 10

• petri dishes and culture media must be sterilised before use,
often done by an autoclave (an oven) or UV light
• innoculating loops must be sterilised by passing them through a flame
• the lid of the Petri dish should be sealed (but not completely)
with tape
• the Petri dish should be stored upside down
• the culture should be incubated at 25 degrees

Question 11

Why must petri dishes and culture media be sterilised before use, often done by an autoclave (an oven) or
UV light?

Answer 11

• likely to be contaminated with other microorganisms if this does not take place
• the contamination could be harmless but will compete with
the desired bacteria for nutrients and space, or they could be harmful (e.g. through a mutation taking place),
potentially producing a new pathogen

Question 12

Why must innoculating loops be sterilised by passing them through a flame?

Answer 12

kills unwanted microorganisms as otherwise they would compete with the desired bacteria for nutrients and space, or they could be harmful (e.g. through a mutation taking place), potentially producing a new pathogen