microbiology

What are microorganisms?

Organisms too small to be seen with the naked eye, including bacteria, viruses, fungi, and protozoa.

Give examples of beneficial microorganisms

• Lactobacillus in yogurt production

• Saccharomyces in bread and alcohol production

• Nitrogen-fixing bacteria in soil

Give examples of harmful microorganisms

• Pathogenic bacteria (e.g., Salmonella)

• Viruses (e.g., influenza)

• Fungi causing disease (e.g., athlete’s foot)

What are the key features of prokaryotic cells (bacteria)?

• No nucleus; DNA in a circular molecule

• Small 70S ribosomes

• Cell wall made of peptidoglycan (murein)

• May have plasmids, flagella, or capsules

How do bacteria reproduce?

Asexually by binary fission, producing genetically identical daughter cells

What is a plasmid?

A small circular DNA molecule separate from the main chromosome; often carries genes for antibiotic resistance.

What is the function of bacterial capsules?

Protect bacteria from phagocytosis and desiccation; help adherence to surfaces.

Are viruses living organisms?

No — they are acellular, lack metabolism, and must infect host cells to reproduce.

What is the structure of a virus?

Genetic material (DNA or RNA) surrounded by a protein coat (capsid); some have lipid envelopes.

How do viruses reproduce?

By infecting host cells and hijacking their machinery to produce new virus particles.

What are the key features of fungi?

• Eukaryotic

• Cell walls made of chitin

• Can be unicellular (yeast) or multicellular (mould)

• Obtain nutrients by absorption (saprotrophic nutrition)

How do protozoa feed?

They are eukaryotic, unicellular, and usually ingest food by phagocytosis

What is meant by the lag phase?

Period after inoculation when microbes are metabolically active but not dividing rapidly.

What is the log (exponential) phase?

Period of rapid cell division and exponential growth.

What is the stationary phase?

Growth rate slows as nutrients become limited and waste accumulates; number of new cells = number of dying cells.

What is the death (decline) phase?

Cells die faster than new ones are produced due to nutrient exhaustion and toxic waste buildup.

What factors affect microbial growth?

Temperature, pH, oxygen availability, water availability, and nutrient supply.

How are microbes used in food production?

• Yeast for bread and alcohol

• Bacteria for yogurt and cheese

• Fungi for soy sauce or antibiotics

How are microbes used in biotechnology?

• Production of insulin using genetically modified bacteria

• Bioremediation to clean up pollutants

• Antibiotic production (e.g., Penicillium for penicillin)

Why are aseptic techniques important in microbiology?

To prevent contamination of cultures and maintain sterile conditions.

What is a pathogen?

A microorganism that causes disease in a host organism.

Give examples of bacterial diseases.

Tuberculosis, cholera, salmonellosis.

Give examples of viral diseases.

Influenza, HIV/AIDS, COVID-19.

How do microbes cause disease?

By producing toxins, destroying cells, or triggering immune responses.

What methods are used to control microbial growth?

• Sterilisation (heat, autoclaving)

• Disinfection (chemicals)

• Antibiotics to inhibit bacterial growth

• Refrigeration to slow growth

Why is microbial resistance a concern?

Overuse of antibiotics can select for resistant strains, making infections harder to treat.