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Microbiology Microscopy and Taxonomy Basics

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  • Define microscopy

    Microscopy is the use of a microscope to view objects that cannot be seen with the naked eye.

  • Relevance of electromagnetic radiation to microscopy

    Electromagnetic radiation provides the light or electron beams used in microscopy to illuminate specimens for visualization.

  • Two factors that determine resolving power

    Resolving power depends on the wavelength of the radiation used and the numerical aperture of the microscope lens.

  • Relationship between contrast and staining in microscopy

    Contrast is enhanced by staining, which colors specimens to distinguish structures more clearly under the microscope.

  • Contrast bright-field, dark-field, and phase microscopy

    Bright-field uses light passing through the specimen; dark-field uses scattered light to view specimens against a dark background; phase microscopy enhances contrast by amplifying differences in refractive index.

  • Compare transmission electron microscopes (TEM) and scanning electron microscopes (SEM)

    TEM transmits electrons through thin specimens to show internal structures; SEM scans surface electrons to produce 3D surface images. TEM offers higher resolution; SEM shows surface details.

  • Purpose of a smear in specimen preparation

    A smear spreads microorganisms on a slide to create a thin layer for microscopic examination.

  • Purpose of heat fixation

    Heat fixation kills microorganisms, adheres them to the slide, and preserves their shape for staining.

  • Purpose of chemical fixation

    Chemical fixation preserves cellular structures by using chemicals to stabilize and fix specimens on slides.

  • Uses of acidic dyes

    Acidic dyes stain the background or negatively charged components, useful for negative staining techniques.

  • Uses of basic dyes

    Basic dyes stain the positively charged components of cells, such as nucleic acids and proteins, highlighting microorganisms.

  • Contrast simple stains and differential stains

    Simple stains use one dye to color all cells similarly; differential stains use multiple dyes to distinguish cell types or structures.

  • Purposes of taxonomy

    Taxonomy organizes and classifies organisms to understand relationships and provide universal names.

  • Difficulties in defining species of microorganisms

    Microorganisms reproduce asexually and exchange genes horizontally, making species boundaries unclear and classification challenging.

  • Hierarchy of taxa from general to specific

    The hierarchy is: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

  • Explain binomial nomenclature

    Binomial nomenclature assigns each organism a two-part Latin name: genus (capitalized) and species (lowercase), e.g., Escherichia coli.

  • How to prepare a heat-fixed smear of a bacterial culture

    Spread bacteria thinly on a slide, air dry, then pass the slide briefly through a flame to fix cells.

  • How to apply simple staining to visualize microorganisms

    Cover a heat-fixed smear with a basic dye, let sit briefly, rinse with water, and blot dry before viewing.

  • Differentiate gram positive and gram-negative microorganisms using staining

    Gram-positive bacteria retain crystal violet stain appearing purple; gram-negative bacteria do not and appear pink/red after counterstaining.