Chapter 3: Cells and Methods to Observe Them Flashcards

This set of 40 vocabulary flashcards covers microscopy principles, staining techniques, prokaryotic morphology, and the anatomy and functions of bacterial cell structures as described in the lecture notes.

Magnification

The apparent increase in size of an object, achieved in a light microscope using a combination of objective and ocular lenses.

Resolution

The ability to distinguish two objects that are very close together; for a light microscope, the maximum resolving power is $0.2\,\mu m$.

Contrast

The factor that determines how easily cells can be seen against a background; it can be increased by staining or specialized microscopy.

Total Magnification (TM)

Calculated by multiplying the power of the ocular lens by the power of the objective lens (e.g., $10\times$ ocular and $100\times$ objective = $1,000\times$ total).

Immersion oil

Used with a $100\times$ lens to reduce light refraction and enhance resolution; it has nearly the same refractive index as glass.

Brightfield Microscope

A type of light microscopy used to view colored or stained specimens.

Darkfield Microscope

Increases contrast of live specimens, making cells appear as bright objects against a dark background.

Phase-Contrast Microscope

Uses special optics to amplify differences between the refractive index of dense material and the surrounding medium to view internal structures of live organisms.

Electron Microscope

Uses electron beams instead of light, providing a resolving power of approximately $0.3\,nm$ and magnification up to $100,000\times$.

Scanning Electron Microscope (SEM)

A type of electron microscope used specifically to observe surface details of a specimen.

Transmission Electron Microscope (TEM)

A type of electron microscope used specifically to view internal details of cells.

Atomic Force Microscope (AFM)

A scanning probe microscope that uses a metal probe to feel the bumps and valleys of atoms, providing detailed images of surfaces.

Smear

A thin layer of cells dried and fixed onto a slide before a staining procedure is performed.

Basic dyes

Dyes carrying a positive charge that bond to and stain the slightly negatively charged bacterial cell; includes Methylene blue and Crystal violet.

Acidic dyes

Dyes carrying a negative charge that are repelled by the cell and commonly stain the background, such as Nigrosin.

Simple stain

A technique using one stain to increase contrast, allowing the size, shape, and arrangement of cells to be observed without differentiating cell types.

Differential Stains

Staining procedures, such as Gram stain and Acid-fast stain, used to distinguish different types of bacteria using a series of reagents.

Gram Stain

Developed by Dr. Hans Christian Gram, this procedure separates bacteria into two major groups based on cell wall structure and chemistry.

Gram-positive bacteria

Bacteria that retain the primary dye and stain purple; characterized by a thick layer of peptidoglycan and teichoic acids.

Gram-negative bacteria

Bacteria that lose the primary dye and stain red or pink; characterized by a thin layer of peptidoglycan and an outer membrane containing LPS.

Acid-fast Stain

Used to detect members of the genus Mycobacterium, which have cell walls with high concentrations of waxy mycolic acid.

Capsule stain

A special staining technique, often a negative stain using acidic dyes, used to observe the gel-like polysaccharide layer surrounding a cell.

Endospore stain

Uses heat to facilitate the uptake of malachite green by dormant structures formed by species of Bacillus and Clostridium.

Flagella stain

Uses dyes that coat and thicken thin protein appendages to make them visible under a light microscope.

Coccus

A spherical-shaped bacterial cell.

Bacillus

A rod or cylinder-shaped bacterial cell.

Spirochete

A bacterial cell with a helical shape.

Pleomorphic

Bacteria that can exhibit many different shapes.

Binary fission

The process by which most prokaryotes divide, often resulting in cells sticking together in characteristic groupings.

Streptococci

Chains of spherical bacteria formed by division along a single plane.

Chemotaxis

Movement where bacteria sense chemicals and move accordingly, using nutrients as attractants and toxic compounds as repellents.

Peptidoglycan (PTG)

A polymer of NAG and NAM cross-linked by tetrapeptide chains found only in the cell walls of bacteria.

Lipopolysaccharide (LPS)

A medically significant component of the Gram-negative outer membrane; contains O-specific polysaccharide and Lipid A (endotoxin).

Periplasm

The region between the cytoplasmic membrane and the outer membrane in Gram-negative bacteria; it contains degradative enzymes.

Active transport

The movement of molecules against a concentration gradient using transporter proteins and energy.

Group transport

A transport mechanism, such as the phosphorylation of glucose, that chemically alters a molecule during its passage across the membrane.

Nucleoid

The region in a prokaryotic cell where the single, circular, double-stranded DNA chromosome is tightly packed.

Plasmids

Extrachromosomal, circular DNA molecules that replicate independently and often encode survival-enhancing traits like antimicrobial resistance.

Prokaryotic Ribosomes

Involved in protein synthesis and designated as $70S$, composed of a $50S$ large subunit and a $30S$ small subunit.

Endosymbiotic theory

The theory that mitochondria and chloroplasts were derived from bacteria, supported by evidence like their circular chromosomes and $70S$ ribosomes.