Microbiology: Microbes, Methods and Meanings
Groups and structure
Know bacteria, archaea, viruses, viroids and prions, and the distinguishing features of prokaryotic cells: no nucleus, 70S ribosomes, peptidoglycan walls in bacteria. Understand bacterial morphology, flagella, pili, capsules and endospores. Learn nutritional types (autotroph, heterotroph, photo- and chemotroph) and growth phases.
Culture and control
Master sterilisation and disinfection methods, culture media, streak plating, and the difference between selective and differential media. Understand antibiotic action, resistance mechanisms and the Gram stain principle. Know the nitrogen cycle and the roles of Rhizobium, Azotobacter, Nitrosomonas and Nitrobacter.
Traps
Examiners test whether archaea have peptidoglycan (they do not), whether viruses are living (a definitional debate), and whether endospores are reproductive (they are survival structures). Another trap is confusing sterilisation with disinfection, or attributing nitrification to a single organism.
Rule of thumb
For any microbe, state the cell type, the energy and carbon source, and the ecological role. This three-part answer resolves most identification questions.
Worked example
A soil sample is plated on a medium containing only a specific carbon source. Only microbes able to use that source grow; this is a selective medium, not a differential one.