Microorganisms: Definitions, Characteristics, and Microbiology Fundamentals

What is a microorganism?

:An organism too small to be seen with the naked eye, including bacteria, archaea, fungi, protozoa, algae, and viruses.

What are the defining characteristics of a microorganism?

:Small size, ability to live in diverse environments, rapid reproduction, and simple cellular organization.

How are all organisms named?

:Using binomial nomenclature: Genus species (italicized, genus capitalized, species lowercase).

What is a prokaryote?

:A unicellular organism without a nucleus or membrane-bound organelles (bacteria, archaea).

What is a eukaryote?

:An organism with a nucleus and membrane-bound organelles (fungi, protozoa, algae, animals, plants).

What are the differences between prokaryotes and eukaryotes?

:Prokaryotes: smaller, no nucleus, circular DNA, binary fission. Eukaryotes: larger, nucleus, linear DNA, mitosis/meiosis.

What are the similarities between prokaryotes and eukaryotes?

:Both have DNA, ribosomes, cytoplasm, plasma membrane.

What is spontaneous generation?

:The idea that life arises from nonliving matter.

How was spontaneous generation disproved?

:Louis Pasteur's swan-neck flask experiment showed microbes come from other microbes.

Which scientists are important in the history of microbiology?

:Leeuwenhoek (microscope), Pasteur (germ theory), Koch (postulates), Lister (antiseptics).

What causes the specific diseases discussed in Unit 1?

:Each disease is caused by specific microorganisms (bacteria, viruses, fungi, protozoa).

What type of microscope do we use in class?

:Compound light microscope.

What are the main differences between different types of microscopes?

:Light microscopes use visible light; electron microscopes use electron beams for higher resolution.

What are magnification, resolution, and contrast?

:Magnification = enlargement; Resolution = clarity/detail; Contrast = ability to distinguish specimen from background.

Which lenses are responsible for magnification?

:Objective lenses + ocular lens.

How do you calculate total magnification?

:Objective lens magnification × ocular lens magnification.

Why do we stain cells?

:To increase contrast and visualize structures.

What types of dyes are used?

:Basic dyes (positive charge) and acidic dyes (negative charge).

What is the principle behind staining?

:Dyes bind to cellular components based on charge and structure.

What is the difference between a simple and a differential stain?

:Simple stain = one dye; Differential stain = multiple dyes to distinguish cell types.

Why is Gram stain common?

:Differentiates bacteria into Gram-positive (purple) and Gram-negative (pink/red).

What is the difference between bacterial cell morphology and colony morphology?

:Cell morphology = shape of individual cells; Colony morphology = appearance of colonies.

What is binary fission?

:Prokaryotic cell division: DNA replication → cell elongation → septum formation → two identical cells.

How do eukaryotes divide?

:By mitosis (growth/repair) or meiosis (gamete formation).

What environmental factors affect bacterial growth?

:Temperature, oxygen, pH, water availability.

What nutritional factors affect bacterial growth?

:Macronutrients (C, H, O, N, P, S) and micronutrients (trace elements).

What is a bacterial growth curve?

:Four phases: lag, log, stationary, death.

What are mixed-microbial associations?

:Communities of different microbes interacting, often enhancing survival.

What is a biofilm?

:Structured microbial community attached to a surface, encased in extracellular matrix.

How do we grow organisms in the lab?

:Using culture media.

What are the classifications of media?

:Complex, chemically defined, selective, differential.

What is a virus?

:An acellular infectious agent requiring a host to replicate.

What are the main classifications of viruses?

:DNA vs. RNA, single vs. double-stranded, enveloped vs. non-enveloped.

Describe the structure of a virus.

:Nucleic acid core + protein capsid ± lipid envelope.

What is the lytic cycle of a bacteriophage?

:Virus infects → replicates → lyses host cell.

How is this different in animal viruses?

:Animal viruses may enter via endocytosis or fusion, and release by budding or lysis.

What happens in a lysogenic cycle?

:Viral DNA integrates into host genome, replicates silently until triggered into lytic cycle.

What is transduction?

:Transfer of bacterial DNA via bacteriophage.

What are the types of viral infection?

:Acute, latent, chronic, slow.

What are characteristics of plant viruses?

:Spread via vectors (insects), mechanical damage, or seeds.

What are viroids?

:Infectious RNA molecules without protein coat, affecting plants.

What are prions?

:Misfolded proteins causing neurodegenerative diseases.

Can you recover from prion infection?

:No, prion diseases are fatal and untreatable.

How can we culture viruses in a laboratory?

:Require living host cells (bacterial cultures, animal cells, embryonated eggs).