Infection & ResponseDeep Dive
Required Practical: Testing Antibacterial Substances
Part of Human Defense Systems - Non-specific — GCSE Biology
This deep dive covers Required Practical: Testing Antibacterial Substances within Human Defense Systems - Non-specific for GCSE Biology. Physical and chemical barriers, white blood cell responses, inflammatory response It is section 10 of 18 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 10 of 18
Practice
19 questions
Recall
22 flashcards
Required Practical: Testing Antibacterial Substances
Aim
To investigate the effectiveness of different antibacterial substances against bacterial growth.
Method
- Prepare agar plates with bacterial culture spread evenly across surface
- Cut paper discs of equal size (approximately 6mm diameter)
- Soak discs in different antibacterial substances (antiseptics, antibiotics, natural substances)
- Include control disc soaked in distilled water
- Use sterile forceps to place discs on bacterial culture, spacing evenly
- Incubate plates at 25°C for 24-48 hours
- Measure diameter of clear zones (zones of inhibition) around each disc
- Calculate area of zones and compare effectiveness
Results and Analysis
- Clear zones: Areas where bacteria cannot grow due to antibacterial substance
- Size correlation: Larger zones indicate more effective substances
- Control importance: Water control should show no clear zone
- Quantitative data: Use area calculations for accurate comparison
Safety and Ethics
- Aseptic technique: Prevent contamination throughout procedure
- Temperature control: Incubate at 25°C, never at body temperature
- Disposal: Autoclave all materials after use
- Hand hygiene: Wash hands thoroughly before and after
Variables
- Independent: Type of antibacterial substance
- Dependent: Diameter/area of zone of inhibition
- Control variables: Temperature, time, disc size, bacterial strain, volume of substance