Introductory Microscopy & Staining – Key Vocabulary

A comprehensive set of vocabulary flashcards covering fundamental concepts of energy, light properties, microscopy techniques, staining methods, and cellular types as presented in the lecture notes.

Energy

Anything in the universe that is not matter; obeys thermodynamic laws and is interpreted as electromagnetic radiation.

Electromagnetic Spectrum

The complete range of electromagnetic energy, only a small portion of which is visible light to the human eye.

Wavelength

The distance between two successive peaks of a light wave; inversely proportional to frequency.

Frequency

The number of light waves that pass a point per unit time; inversely proportional to wavelength.

Amplitude

The height of a light wave; relates to the amount of energy the wave carries.

Velocity of Light

The speed at which light travels; can vary in different media and is not perfectly constant.

Bright-Field Microscope

The common light microscope in which light passes through a specimen and a series of lenses to form an image.

Magnification

The apparent increase in size of an object produced by a microscope’s lenses.

Resolution (Resolving Power)

The ability of a microscope to distinguish two points that are close together as separate objects.

Contrast

The difference in light intensity between a specimen and its background, determining image visibility.

Refraction

The bending of light as it passes through materials with differing optical densities.

Refractive Index

A numerical value describing how much a medium bends (refracts) light relative to air.

Immersion Oil

Oil with a refractive index (~1.518) similar to glass; reduces light refraction and improves resolution at high magnifications.

Par-Focal

Microscope design in which once an image is in focus with one objective, it remains nearly in focus when switching objectives.

Working Distance

The space between the objective lens and the specimen when the image is in focus.

Reflection (Light)

Light bouncing off a surface without entering the material.

Transmission (Light)

Light passing through a material without being absorbed.

Absorption (Light)

Light energy taken up by a material, often converted to heat or re-emitted at a different wavelength.

Dark-Field Microscopy

Technique that illuminates specimens against a dark background by blocking central light rays and collecting only scattered light.

Phase-Contrast Microscopy

Light microscopy that exaggerates differences in refractive index to increase contrast in unstained, living cells.

Differential Interference Contrast (DIC)

Microscopy using dual beams and polarized light to create high-contrast, 3-D-like images based on refractive index differences.

Fluorescence Microscopy

Microscopy that visualizes specimens stained with fluorochromes that absorb and emit light of specific wavelengths.

Scanning Laser Microscope (SLM)

Laser-based fluorescence system that optically sections thick specimens to build three-dimensional images.

Electron Microscopy (EM)

Imaging technique using electron beams for extremely high magnification; requires vacuum and complex preparation.

Transmission Electron Microscope (TEM)

EM type that passes electrons through ultra-thin specimens to reveal internal structures.

Scanning Electron Microscope (SEM)

EM type that scans a specimen’s surface with electrons to produce detailed 3-D exterior images.

Chromophore

The colored, light-absorbing part of a dye molecule.

Acidic Dye

Stain whose chromophore carries a negative charge; repelled by negatively charged cell surfaces, often staining the background.

Basic Dye

Stain whose chromophore carries a positive charge; attracted to negatively charged bacterial cells and commonly used in microbiology.

Neutral Dye

Stain containing both acidic and basic chromophores; example: Giemsa.

Simple Stain

Slide technique using a single dye to color all cells for basic morphology and arrangement.

Differential Stain

Technique employing two dyes so that different cell types or structures retain distinct colors (e.g., Gram stain).

Structural Stain

Staining protocol targeting specific cell structures or molecules, such as spores or capsules.

Wet Mount

Slide preparation of living organisms in liquid; allows observation of natural movement without staining.

Hanging Drop

Wet-mount method using a concave slide to suspend a drop, enhancing viewing of motility.

Smear

Thin film of microorganisms air-dried on a slide and heat-fixed for staining.

Heat Fixation

Gentle heating of a smear to kill cells, adhere them to the slide, and preserve morphology.

Gram Stain

Differential stain separating bacteria into Gram-positive (purple) and Gram-negative (pink) based on peptidoglycan thickness.

Peptidoglycan

Rigid polysaccharide-peptide component of bacterial cell walls; thick in Gram-positive, thin in Gram-negative bacteria.

Acid-Fast Stain

Differential stain detecting mycolic-acid-rich cell walls of Mycobacterium and Nocardia.

Mycolic Acid

Waxy lipid in certain bacterial cell walls responsible for acid-fast staining properties.

Negative Stain

Staining technique that colors the background but leaves cells unstained, revealing capsules or slime layers.

Endospore Stain (Schaeffer-Fulton)

Differential stain using malachite green to color bacterial spores and a counterstain for vegetative cells.

Extracellular Polymeric Layer

Gel-like outer layer (capsule or slime) that aids in biofilm formation and resists staining.

Capsule

Well-defined, protective extracellular layer surrounding some bacteria; visible with negative staining.

Slime Layer

Diffuse, loosely attached extracellular layer; assists in surface adherence and biofilm formation.

Prokaryotic Cell

Cell lacking a nucleus; typically smaller and characteristic of Bacteria and Archaea.

Eukaryotic Cell

Cell with a true nucleus and membrane-bound organelles; found in plants, animals, fungi, and protists.