Chapter 2: A Brief Journey to the Microbial World

Question 1

Bright-field scope

Answer 1

Specimens are visualized
because of differences in
contrast (density) between
specimen and surroundings

Question 2

Objective lens and ocular lens calculation

Answer 2

• Total magnification = objective
magnification x ocular
magnification
• Maximum magnification is
~2,000x

Question 3

Resolution:

Answer 3

– the ability to distinguish two adjacent
objects as separate and distinct
– Resolution is determined by the wavelength of light
used and numerical aperture of lens
– Limit of resolution for light microscope is about
0.2 u m

Question 4

True or false: Improving contrast results in a better final image

Answer 4

True

Question 5

Staining improves contrast

Answer 5

• Dyes are organic compounds that bind to specific cellular
materials
• Examples of common stains are methylene blue, safranin,
and crystal violet (basic dyes)

Question 6

Bacteria can be divided into two
major groups:

Answer 6

gram-positive and
gram-negative

Question 7

Differential stains: the Gram stain

Answer 7

Differential stains separate bacteria
into groups

Question 8

Phase-Contrast Microscopy

Answer 8

• Invented in 1936 by Frits Zernike
• Phase ring amplifies differences in
the refractive index of cell and
surroundings
• Improves the contrast of a sample
without the use of a stain
• Allows for the visualization of live
samples
• Resulting image is dark cells on a
light background (Figure 2.5b)

Question 9

Dark-Field Microscopy

Answer 9

• Light reaches the specimen from
the sides
• Light reaching the lens has been
scattered by specimen
• Image appears light on a dark
background (Figure 2.5c)
• Excellent for observing motility

Question 10

Fluorescence Microscopy

Answer 10

• Used to visualize specimens that
fluoresce
• Emit light of one color when
illuminated with another color of light
• Cells fluoresce naturally
(autofluorescence) or after they
have been stained with a
fluorescent dye like DAPI
• Widely used in clinical diagnostic
microbiology, microbial ecology for
enumerating bacteria in natural
samples, or in cell suspension

Question 11

Differential Interference Contrast
(DIC) Microscopy

Answer 11

• Uses a polarizer to create two
distinct beams of polarized light
• Gives structures such as
endospores, vacuoles, and granules
a three-dimensional appearance
(Figure 2.7a)
• Structures not visible using brightfield microscopy are sometimes
visible using DIC without staining

Question 12

Atomic Force Microscopy (AFM)

Answer 12

• A tiny stylus is placed close to a
specimen
• The stylus measures weak repulsive
forces between it and the specimen
• A computer generates an image
based on the data received from
the stylus

Question 13

Confocal Scanning Laser
Microscopy (CSLM)

Answer 13

• Uses a computerized microscope
coupled with a laser source to
generate a three-dimensional
image (Figure 2.8)
• Computer can focus the laser on
single layers of the specimen
• Different layers can then be
compiled for a three-dimensional
image
• Resolution is 0.1  m for CSLM

Question 14

Electron Microscopy

Answer 14

• Electron microscopes use electrons
instead of photons to image cells and
structures
• Two types of electron microscopes:
• Transmission electron microscopes (TEM)
• Scanning electron microscopes (SEM)

Question 15

Transmission Electron Microscopy
(TEM)

Answer 15

• Electromagnets function as lenses
• System operates in a vacuum
• High magnification and resolution
(0.2 nm)
• Enables visualization of structures
at the molecular level (Figure 2.10a
and b)
• Specimen must be very thin (20–60
nm) and be stained

Question 16

Scanning Electron Microscopy
(SEM)

Answer 16

• Specimen is coated with a thin film
of heavy metal (e.g., gold)
• An electron beam scans the object
• Scattered electrons are collected by
a detector and an image is
produced (Figure 2.10c)
• Even very large specimens can be
observed
• Magnification range of 15–
100,000 but only the surface of an
object is visualized

Question 17

All cells have the following in common:

Answer 17

• Cytoplasmic membrane
• Cytoplasm
• Ribosomes

Question 18

Elements of Microbial Structure: Eukaryotes

Answer 18

• DNA enclosed in a membrane bound nucleus
• Cells are generally larger and more complex
• Contain organelles

Question 19

Elements of Microbial Structure: Prokaryotes

Answer 19

No membrane-enclosed organelles, no nucleus

Generally smaller than eukaryotic cells

Question 20

Viruses

Answer 20

• Not considered cells
• No metabolic abilities of their own
• Rely completely on biosynthetic
machinery of infected cell
• Infect all types of cells
• Smallest virus is 10 nm in diameter

Question 21

Genome

Answer 21

A cell’s full complement of genes

Question 22

Prokaryotic cells generally have a
single, circular DNA molecule called

Answer 22

chromosome

Question 23

Plasmids

Answer 23

Prokaryotes also may have small
amounts of extra-chromosomal DNA
called plasmids that confer special
properties (e.g., antibiotic resistance)

Question 24

Eukaryotic DNA is linear and found within the nucleus

Answer 24

• Associated with proteins that help in folding of the DNA
• Usually more than one chromosome
• Typically two copies of each chromosome
• During cell division, nucleus divides by mitosis
• During sexual reproduction, the genome is halved by
meiosis

Question 25

Arrangement of DNA in Microbial Cells: Escherichia coli Genome

Answer 25

• 4.64 million base pairs
• 4,300 genes
• 1,900 different kinds of protein
• 2.4 million protein molecules

Question 26

Arrangement of DNA in Microbial Cells: Human Cell

Answer 26

• 1,000x more DNA per cell than E. coli
• 7x more genes than E. coli

Question 27

Evolution

Answer 27

The process of change over time that results in new varieties and species of organisms

Question 28

Phylogeny

Answer 28

• Evolutionary relationships between organisms
• Relationships can be deduced by comparing genetic information in the different specimens
• Ribosomal RNA (rRNA) is excellent for determining phylogeny
• Relationships visualized on a phylogenetic tree

Question 29

Comparative rRNA sequencing has defined three distinct lineages of cells called domains:

Answer 29

• Bacteria (prokaryotic)
• Archaea (prokaryotic)
• Eukarya (eukaryotic)

Question 30

Endosymbiosis

Answer 30

a term used to describe two organisms living together with one inside the other

Question 31

ancestors of multicellular organisms

Answer 31

eukaryotic microorganisms

Question 32

Metabolic Diversity

Answer 32

• The diversity in microbial cells is the product of
almost 4 billion years of evolution
• Microorganisms differ in size, shape, motility,
physiology, pathogenicity, etc.
• Microorganisms have exploited every conceivable
means of obtaining energy from the environment

Question 33

Chemoorganotrophs

Answer 33

• Obtain their energy from the
oxidation of organic molecules
• Aerobes use oxygen to obtain energy
• Anaerobes obtain energy in the
absence of oxygen

Question 34

Chemolithotrophs

Answer 34

• Obtain their energy from the
oxidation of inorganic molecules
• Process found only in prokaryotes

Question 35

Phototrophs

Answer 35

• Contain pigments that allow them to
use light as an energy source
• Oxygenic photosynthesis produces
oxygen
• Anoxygenic photosynthesis does not
produce oxygen

Question 36

All cells require ________ as a major nutrient

Answer 36

carbon

Question 37

Autotrophs use this as their carbon source

Answer 37

Carbon dioxide

Question 38

Sometimes referred to as primary producers

Answer 38

Autotrophs

Question 39

Heterotrophs

Answer 39

• Require one or more organic molecules for their carbon source
• Feed directly on autotrophs or live off products produced by
autotrophs

Question 40

extremophiles

Answer 40

organisms that inhabit extreme environments are
called

Question 41

Habitats of extremophiles

Answer 41

Habitats include boiling hot springs, glaciers, extremely salty bodies of water, and high-pH environments

Question 42

All known pathogenic
prokaryotes are

Answer 42

Bacteria

Question 43

Make up the largest phylum of Bacteria

Answer 43

Proteobacteria

Question 44

Gram-negative bacteria examples

Answer 44

E. coli, pseudomonas, salmonella

Question 45

Photosynthetic bacterias

Answer 45

Green sulfur and green nonsulfur bacteria

Question 46

Bacteria extremely resistant to radioactivity

Answer 46

Deinococcus

Question 47

Obligate intracellular parasites

Answer 47

Chlamydia

Question 48

Two Phyla of the Domain
Archaea

Answer 48

Euryarchaeota and crenarchaeota

Question 49

Euryarchaeota

Answer 49

• Methanogens: degrade organic
matter anaerobically, produce
methane (natural gas)
• Extreme halophiles: require high
salt concentrations for
metabolism and reproduction
• Thermoacidophiles: grow in
moderately high temperatures
and low-pH environments

Question 50

Crenarchaeota

Answer 50

• Vast majority of cultured Crenarchaeota are hyperthermophiles
• Some live in marine, freshwater,
and soil systems

Question 51

Ribosomal RNA are uses to infer evolutionary relationships between
organisms. Woese recognized genes encoding rRNA are:

Answer 51

(1) Universally distributed
(2) Functionally constant
(3) Highly conserved (slowly changing)
(4) Adequate length to provide a deep view of evolutionary relationships

Question 52

Eukaryotic microorganisms include

Answer 52

algae, fungi, protozoa, and slime
molds

Question 53

True or false: algae and protozoa are phototrophic

Answer 53

False

Question 54

Algae and fungi have _________,
whereas protozoa and slime molds do
not

Answer 54

cell walls

Question 55

mutualistic relationship
between two groups of protists

Answer 55

lichens

Question 56

Examples of lichens

Answer 56

• Fungi and cyanobacteria
• Fungi and algae