Microbiology and Microbial Biotechnology
What the domain covers
Microbiology and microbial biotechnology tests microbial structure, classification, growth, cultivation, control of microorganisms, fermentation, and industrial uses of microbes. Expect questions on growth curves, media, sterilisation, gram staining, bioreactors, antibiotics, and food or environmental microbiology.
Core rules and concepts
- Bacteria are prokaryotes; their cell walls contain peptidoglycan. Gram-positive cells retain crystal violet-iodine and stain purple; gram-negative cells decolourise and counterstain pink.
- A batch growth curve has lag, log (exponential), stationary, and death phases. Generation time is the time for the population to double during log phase.
- Sterilisation kills or removes all viable organisms; disinfection reduces pathogens on surfaces but may not sterilise. Autoclaving typically uses 121 °C at 15 psi for 15–20 minutes.
- Media may be defined or complex, selective or differential. Anaerobes require oxygen-free conditions.
- Industrial fermentation uses bioreactors to control temperature, pH, aeration, and mixing; primary metabolites form during growth, secondary metabolites often near stationary phase.
Worked example
A culture grows from 10³ to 10⁶ cells in 3 hours. There are three doublings (10³→10⁴→10⁵→10⁶), so generation time is 3 h ÷ 3 = 1 h. Reasoning: each doubling multiplies by 2; count doublings from the exponent difference, then divide elapsed time by that number.
Traps
Do not use “sterilisation” for wiping a bench with alcohol. Do not count the lag phase as exponential growth. Do not say antibiotics kill viruses. Do not assume all bacteria grow on the same medium or in air.