Chapter 2 Key Terms

Front 1

Aberration

Back 1

An imperfection in a lens

Front 2

Absorption

Back 2

In optics, the capacity of a material to absorb light.

Front 3

Acid-fast stain

Back 3

A diagnostic stain for mycobacteria, which retain the dye fuchsin due to the presence mycolic acids in the cell wall.

Front 4

Airy disk

Back 4

A bright central point surrounded by rings of light and dark caused by the pattern of interference of spherical wave-fronts converging at the focal point.

Front 5

Angle of aperture

Back 5

The width of a light cone (theta) that projects from the midline of a lens. Greater angles of aperture increase resolution.

Front 6

Antibody stain

Back 6

The attachment of a stain to an antibody to visualize cell components recognized by the antibody with high specificity.

Front 7

Artifact

Back 7

A structure viewed through a microscope that is incorrectly interpreted.

Front 8

Atomic Force Microscopy (AFM)

Back 8

A technique that maps the three dimensional topography of a object using van der Waals forces between the object and a probe.

Front 9

Bacillus

Back 9

A bacterium with a linear, rod-like shape.

Front 10

Bright-Field Microscopy

Back 10

A type of light microscopy in which the specimen absorbs light and appears dark against a light background.

Front 11

Coccus

Back 11

A spherically shaped microbial cell

Front 12

Compound Microscope

Back 12

A microscope with multiple lenses to compensate for lens aberration and increase magnification.

Front 13

Condenser

Back 13

A lens that focuses parallel light rays from the light source onto a small area of the specimen to improve the resolution of the objective lens.

Front 14

Contrast

Back 14

Differential absorption or reflection of electromagnetic radiation between an object and background that allows the object to be distinguished from the background.

Front 15

Counterstain

Back 15

A secondary stain used to visualize cells that do not retain the first stain.

Front 16

Cryocrystallography

Back 16

X-ray crystallography on crystals that are flash-cooled in liquid nitrogen

Front 17

Cryoelectron Microscopy (cryo-EM)

Back 17

Electron microscopy in which the sample is cooled rapidly in a cryoprotectant medium that prevents freezing. The sample does not need to be stained.

Front 18

Dark-field Microscopy

Back 18

The detection of microbes too small to be resolved by light rays by observing the light rays they scatter.

Front 19

Depth of field

Back 19

A region of the optical column over which a specimen appears in reasonable focus.

Front 20

Detection

Back 20

The ability to determine the presence of an object.

Front 21

Diaphragm

Back 21

A device in a microscope to vary the diameter of the light column, changing the amount of light admitted.

Front 22

Differential stain

Back 22

A stain that differentiates among objects by staining only particular types of cells or specific sub-cellular structures.

Front 23

Electron Microscope

Back 23

A microscope that obtains high resolution and magnification by focusing electron beams on samples using magnetic lenses.

Front 24

Emission Wavelength

Back 24

The wavelength of light emitted by a fluorescent molecule. It is of a lower energy and longer wave-length than the excitation wavelength.

Front 25

Empty Magnification

Back 25

Magnification without an increase in resolution.

Front 26

Excitation Wavelength

Back 26

The wavelength of light that must be absorbed by a molecule in order for the molecule to fluoresce.

Front 27

Fixation

Back 27

The adherence of cells to a slide by a chemical or heat treatment.

Front 28

Flagella

Back 28

A filimentous structure for motility. In prokaryotes, a helical protein filament attached to a rotary motor; in eukaryotes an undulating cell membrane-enclosed complex of microtubules and ATP driven motor proteins.

Front 29

Fluorescence

Back 29

The emission of light from a molecule that absorbed light of a shorter, higher energy wavelength.

Front 30

Fluorophore

Back 30

A fluorescent molecule used to stain specimens for fluorescent microscopy.

Front 31

Focal plane

Back 31

A plane that contains the focal point for a given lens.

Front 32

Focal point

Back 32

The position at which light rays that pass through a lens intersect.

Front 33

Focus

Back 33

A group of cells infected by a virus.

Front 34

Gram stain

Back 34

A differential stain that distinguishes between cells that possess a thick cell wall and retain a positively-charged stain (gram-positive) from cells with a thin cell wall and outer membrane that fail to retain the stain (gram-negative).

Front 35

Gram-negative

Back 35

Cells that do not retain the Gram stain.

Front 36

Gram-positive

Back 36

Cells that do retain the Gram stain and appear dark purple after staining.

Front 37

Immersion oil

Back 37

An oil with a refractive index similar to glass that minimizes light ray loss at wide angles, thereby minimizing wavefront interference and maximizing resolution.

Front 38

Interference

Back 38

The interaction of two wavefronts. Interference can be additive (amplitudes in phase, constructive) or subtractive (amplitudes out of phase, destructive).

Front 39

Interference Microscopy

Back 39

Observation of an object using contrast enhanced by superimposing interference bands upon an image to accentuate small differences in refractive indexes.

Front 40

Laser scanning confocal microscopy

Back 40

A type of fluorescence microscopy in which the excitation and emitted light are focused together, producing high resolution images.

Front 41

Light microscopy

Back 41

Observation of a microscopic object based on light absorption and transmission.

Front 42

Magnification

Back 42

An increase in the apparent size of a viewed object as an optical image.

Front 43

Microscope

Back 43

A tool that increases that magnification of specimens to enable viewing at higher resolution.

Front 44

Mordant

Back 44

A chemical binding agent that causes specimens to retain stains better.

Front 45

Negative stain

Back 45

A stain that colors the background and leaves the specimen unstained.

Front 46

Nuclear Magnetic Resonance (NMR)

Back 46

A technique that provides structural information based on the absorption and emission of electromagnetic radiation resulting from changes in the spin state of atomic nuclei.

Front 47

Numerical Aperature (NA)

Back 47

The product of the refractive index of the medium and sin theta. As NA increases the magnification increases.

Front 48

Objective lens

Back 48

In a compound microscope, the lens closest to the specimen that generates the initial magnification.

Front 49

Ocular lens

Back 49

In a compound microscope, the lens situated closest to the observer's eye. It is also called the eyepiece.

Front 50

Parfocal

Back 50

In a microscope with multiple objective lenses, having the objective lens set at different heights that maintain focus when switching among lenses.

Front 51

Reflection

Back 51

Deflection of an incident light ray by an object, at an angle equal to the incident angle.

Front 52

Refraction

Back 52

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Front 53

Refractive Index

Back 53

The degree to which a substance causes the refraction of light, a ratio of the speed of light in a vacuum to its speed in another medium.

Front 54

Resolution

Back 54

The smallest distance that two objects can be separated and still be distinguished as separate objects.

Front 55

Rods

Back 55

1) A bacteria with a linear shape (also referred to as a bacillus). 2) A photoreceptor cell.

Front 56

Scanning Electron Microscopy (SEM)

Back 56

Electron microscopy in which the electron beams scan accross the specimen's surface to reveal the three-dimensional topology of the specimen.

Front 57

Scattering

Back 57

Interaction of light with an object resulting in propagation of spherical light waves at relatively low intensity.

Front 58

Simple Stain

Back 58

A stain that makes an object more opaque, increasing its contrast with the external medium or surrounding tissues.

Front 59

Spirochete

Back 59

A bacterium with a tight, flexible spiral shape; a species of the phylum Spirochetes (Spirochaetes).

Front 60

Spore Stain

Back 60

A type of differential stain that is specific for the endospore coat of various bacteria, typically a firmicute species.

Front 61

Staining

Back 61

The process of treating microscopic specimens with a stain to enhance their detection or to visualize specific cell components.

Front 62

Tomography

Back 62

The acquisition of projected images of a transparent specimen from different angles that are digitally combined to visualized the entire specimen.

Front 63

Total Magnification

Back 63

The magnification of the ocular lens multiplied by the magnification of the objective lens.

Front 64

Transmission Electron Microscopy (TEM)

Back 64

A type of electron microscopy in which electron beams are transmitted through a thin specimen to reveal internal structure.

Front 65

Wet Mounts

Back 65

A technique to view living microbes with a microscope by placement of the microbes in water on a slide under a coverslip.

Front 66

X-Ray Crystallography

Back 66

A technique to determine the positions of atoms (atomic coordinates) within a molecule or molecular complex, based upon the diffraction of X-rays by the molecule.

Front 67

X-Ray Diffraction Analysis

Back 67

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Front 68

van der Waals force

Back 68

Weak, temporary electrostatic attraction between molecules caused by shifting electron clouds.