2 Microbiology Laboratory Foundations Free Online FlashCards

How is total magnification calculated?

Total magnification equals objective magnification multiplied by ocular magnification. A 100× objective with a 10× ocular gives 1,000× total magnification.

What does resolution describe in microscopy?

Resolution is the ability to distinguish two nearby points as separate. Greater magnification without better resolution enlarges the image but does not make it clearer.

How does oil immersion improve high-magnification viewing?

Oil immersion reduces light refraction between the slide and objective lens, improving resolution at high magnification.

What contrast does phase-contrast and darkfield microscopy provide?

Phase-contrast microscopy can show unstained cells; darkfield microscopy makes specimens appear bright against a dark background.

What information does a simple stain reveal?

A simple stain uses one dye to reveal cell shape and arrangement.

What is the purpose of a differential stain?

A differential stain uses multiple reagents to distinguish groups of cells based on structural differences.

How do Gram-positive and Gram-negative cells typically appear?

Gram-positive cells generally retain the primary stain and appear purple; Gram-negative cells are decolorized and take up the counterstain, appearing pink or red.

Why does a Gram-stain result not prove a species identity?

Gram-stain results are evidence for identification, not proof of species. Smear thickness, culture condition, reagent timing, and decolorization can affect the result.

How do aseptic technique and sterilization differ?

Sterilization destroys or removes all forms of microbial life from an item; aseptic technique reduces unwanted microbial transfer during handling.

How can a sterile loop become contaminated during handling?

Use a new or properly sterilized tool for each transfer. A sterile loop can become contaminated if it touches a nonsterile surface after sterilization.

What is a microbial colony, and what can its appearance tell you?

A colony is a localized microbial population that typically began from one cell or a small group of cells. Its appearance can offer clues but does not establish identity by itself.

How does the streak-plate method help isolate colonies?

In streak plating, inoculum is spread across successive agar areas so fewer cells are deposited in each area. Well-separated colonies can then be selected as isolated cultures.