BiologyGrade 12Microorganisms

Microbiology Lab: Bacterial Growth and Antibiotics

Culture bacteria under different temperature, pH, nutrient, and antibiotic conditions, then measure growth rate, colony count, and inhibition zone.

SimulationsLab index
Textbook unitMicroorganismsGrade 12 Biology Unit 2
Keywordsmicroorganisms, bacteria, growth, culture, antibioticMapped to available textbook headings
Practice modeManipulate, measure, explainUse the controls, then read the live evidence

Biology ยท Grade 12

Microbiology Lab: Bacterial Growth and Antibiotics

Culture bacteria under controlled conditions, adjust antibiotic dose, and use colony count plus inhibition zone evidence to judge growth control.

StatusSuppressed culture
1

Run an untreated culture under near-optimum conditions and record the baseline colony count.

2

Increase antibiotic dose until the plate shows a clear inhibition zone and low survival.

3

Change temperature or pH away from optimum and explain how stress changes growth.

58 ug
Standard agar22 colonies
Incubator37 C18 h elapsed
Growth curve0.36 rate
Colonies222 % survival index
Inhibition zone58 mm58 ug antibiotic disk
Stress index5 %37 C, pH 7.0
Doubling time16.0 h
Oxygen use22 %
Growth risk5 %
Microbiology insight

Suppression threshold reached: 58 ug creates a 58 mm inhibition zone and keeps the colony count at 22.

Colony count22
Growth rate0.36 rate
Inhibition zone58 mm
Oxygen use22 %
Growth risk5 %

Lab task

Find a dose and culture condition that keeps colony growth controlled while preserving a measurable inhibition zone around the antibiotic disk.

Observation rule

Bacteria grow fastest near optimum temperature and pH. Antibiotics reduce survival and create clear zones where colonies fail to establish.

Mission

What to prove in this lab

  1. Explain how temperature, pH, and nutrients affect bacterial growth.
  2. Use antibiotic dose to compare colony survival and inhibition zone size.
  3. Interpret growth curves and colony counts as evidence for microbial control.