Investigating Natural Selection
Biology: AQA A Level, topic 4.4.5
Investigating Microbial Growth
The effect of antimicrobial substances on the growth of microorganisms can be investigated using the following steps:
1) Make conditions aseptic
- It is important to make sure the conditions for the experiment are aseptic.
- This prevents the growth of any unwanted microorganisms that might affect the results.
- Aseptic techniques include:
- Disinfect surfaces.
- Sterilise equipment to destroy microorganisms.
- Flame the necks of bottles on opening.
2) Spread bacteria
- Use a pure culture of bacteria to make a lawn spread on a petri dish.
3) Place the antibiotic ring
- Place an antibiotic ring on the surface.
- Place the lid of the petri dish on and secure loosely with tape.
- Do not completely tape shut the lid to allow the flow of oxygen and prevent the growth of anaerobic bacteria.
4) Incubate
- Incubate the petri dish upside down for 24-48 hours to allow the bacteria to grow.
- Incubating upside down prevents condensation from dripping onto the agar.
5) Observe growth patterns
- Observe the patterns of growth of microorganisms.
- You should see a zone of inhibition around the antibiotic ring where no microorganisms have grown.
- Measure the zone of inhibition.
Test yourself on Investigating Natural Selection
Stages Involved in Investigating Microbial Growth
What is the zone of inhibition?
Which of these statements about investigating natural selection are true?