Ch.3 Observing Microorganisms Through a Microscope

Vocabulary flashcards focusing on microscopic techniques, optical principles, compound light microscope parts, and bacterial staining methods from Chapter 3.

Total Magnification

The overall enlargement of a specimen image in a compound light microscope, calculated using the formula $\text{Total magnification} = \text{objective lens} \times \text{ocular lens}$.

Resolution

The ability of microscope lenses to distinguish two separate points; shorter wavelengths of light provide greater resolution.

Refractive Index

A measure of the light-bending ability of a given medium.

Immersion Oil

An oil used with an oil immersion objective lens to keep light from refracting and being lost after passing through a specimen.

Brightfield Microscopy

A type of compound light microscopy in which dark objects are visible against a bright background, and light reflected off the specimen does not enter the objective lens.

Darkfield Microscopy

A microscopy technique that uses a condenser with an opaque disk so that light objects are visible against a dark background from light reflected off the specimen.

Phase-Contrast Microscopy

A microscopy technique that allows the examination of living organisms and internal cell structures by combining direct light rays and diffracted light rays to form an image.

Ocular Lens

The eyepiece lens of a microscope that remagnifies the image formed by the objective lens.

Objective Lens

The primary lenses on a microscope that magnify the specimen.

Condenser

A microscope component located beneath the stage that focuses light directly through the specimen.

Diaphragm

A microscope component that controls the amount of light entering the condenser.

Smear

A thin film of a material containing microorganisms spread over a glass slide and fixed using heat.

Staining

The procedure of coloring microorganisms with a dye to emphasize specific cellular structures.

Basic Dye

A dye whose chromophore is a positively charged cation ($\text{Basic}/+$) that binds directly to negatively charged bacterial cell structures.

Acidic Dye

A dye whose chromophore is a negatively charged anion ($\text{Acidic}/-$), which is repelled by negatively charged cells and stains the background instead.

Negative Staining

A staining procedure in which the background is colored instead of the cell.

Simple Stain

The use of a single basic dye to highlight an entire microorganism so that cell shapes and structures can be visualized.

Mordant

A fixative agent (such as iodine or heat) that combines with a dye or stain to intensify it, increase its affinity for a biological specimen, or coat structures like flagella to make them thicker.

Differential Stains

Stains that react differently with different kinds of bacteria (such as Gram stains and acid-fast stains) and are used to distinguish between them.

Gram Stain

A differential staining technique using crystal violet primary stain, iodine mordant, alcohol decolorizer, and safranin counterstain to classify bacteria into Gram-positive or Gram-negative.

Acid-Fast Stain

A differential stain that binds to bacteria containing waxy material in their cell walls using carbolfuchsin primary stain, acid-alcohol decolorizing agent, and methylene blue counterstain.

Capsule Stain

A special negative staining technique using a suspension of India ink or nigrosin to contrast the background against gelatinous bacterial capsules, which appear as halos around the cells.

Endospore Stain

A special staining method that uses malachite green with heat/steam as a mordant, water as a decolorizer, and safranin counterstain to reveal resistant dormant endospores (green) inside cells (pink/red).

Flagella Stain

A special staining technique that uses a mordant and carbolfuchsin to build up and thicken locomotion structures (flagella) so they become visible under a light microscope.