WGU Clinical Microbiology Exam 1
Questions and Answers
Discuss what is meant by "growth" when referring to microbes and the ways in which
it can be measured (describe the growth curve phases).(CORRECT ANSWERS)
Microbial growth is the increase in the number of cells in a culture. The increase in
number of cells occurs by cell division. This cell division usually occurs via binary
fission or budding. In binary fission, a cell duplicates its components and divides into
two separate cells. In budding, a small, new cell develops from the surface of an
existing cell and subsequently separates from the parent cell. There are four major
phases of microbial growth: 1) the lag phase. 2) The log phase. 3) The stationary
phase. 4) The decline/ death phase. The lag phase occurs when bacterium are first
transferred to a new culture. No bacterial growth occurs in the lag phase, instead the
bacterium are increasing in size, synthesizing enzymes, and absorbing nutrients
from the new medium. The length of this phase is determined by their genetics and
the condition of medium. Once the organisms have adapted to the medium, the log
phase begins. The log phase is a time of logarithmic growth (exponential growth).
During this time the organisms divide at their fastest rate. In a hypothetical situation
synchronous growth occurs. In synchronous growth, the population doubles every 20
min. However, in a real situation, some organisms take longer to go from the lag
phase to the log phase and they do not all divide at the same rate. In
nonsynchronous growth, about 1/20 or the organisms divide each minute. The time it
takes for the population to double is called generation time. When cell division
decreases to the point that new organisms are produced at the same rate organisms
are dying, the culture as reached the stationary phase. In this phase, the medium
contains a limited amount of nutrients are possibly large amounts of toxic waste. The
oxygen supply may be inadequate for aerobic organisms and damaging pH levels
may occur. The decline/ death phas
The type of cell reproduction in which small, new cells develop from the surface of an
existing cell and then separate from the parent cell is known as ____________ and
is the normal mode of replication in__________.(CORRECT ANSWERS) Budding,
yeasts.
Microbial growth(CORRECT ANSWERS) In a single generation time leads to double
the number of cells.
a bacterial culture can be kept in the log phase of growth indefinitely with the help of
a(CORRECT ANSWERS) chemostat
Which of the following bacterial counting methods relies on a statistical estimate to
determine the number of bacteria in a culture?(CORRECT ANSWERS) most
probable number
Most bacteria(CORRECT ANSWERS) do not immediately increase in number when
placed in a culture.
, Bacterial growth in colonies on agar plates______.(CORRECT ANSWERS) have all
phases of growth occurring simultaneously somewhere in the colony.
Acidophiles would be expected to growth best at a pH of(CORRECT ANSWERS) 3
Most human pathogenes are(CORRECT ANSWERS) mesophiles
Which type of cell generally shift to aerobic metabolism when oxygen is available but
will carry on fermentation otherwise.(CORRECT ANSWERS) faculative anaerobes
The toxic effects of the byproducts of oxygen metabolism are reduced by which of
the following?(CORRECT ANSWERS) catalase and superoxide dismutase.
Review the physical and nutritional factors that can influence microbial
growth.(CORRECT ANSWERS) Physical factors affecting microbial growth include
pH, temperature, quantity of oxygen, water, hydrostatic pressure, and osmotic
pressure. Microorganisms have an optimum pH- a pH at which they growth their
best. According to their tolerance of pH, bacteria are classified as acidophiles (.1-
5.4pH), neutrophiles (5.4-8.0), and alkaliphiles (7.0-11.5). Most of the disease
causing bacteria in humans are neutrophiles. Changes in pH can lead to denaturing
enzymes and other proteins and can interfere with pumping of ions through the cell
membrane. Other organisms appear to tolerate environmental acidity or alkalinity
because the cell itself is maintained at a nearly neutral pH because their cell walls
are relatively impervious so the cell wall protects the cell membrane from being
exposed to the extreme pH in the medium.
Most organisms can grow within a range of 30 degrees around their optimum
temperature. ACcording to the temperature range for growth, bacteria are classifed
as phychrophiles (cold-loving), mesophiles (room-temp), and thermophiles (heat-
loving). Obligate means that the organisms must have the specified environmental
condition. Faculative means that the organism is able to adjust and tolerate the
environmental condition but it it also able to live in other conditions. Mesophiles
include most bacteria and pretty much all human pathogens. The temperatyre range
over whch an organism grows is determined largely by the temperatures at which
enzymes function. Minimum growth rate occurs at the lowest temperature at which
cells can divide. Maximum growth rate occurs near the highest temperature at which
the cells can divide. The temperature range over which an organism grows is
determined largely by the temperatures at which enzymes function. Oxygen
concentration also effects bacterial growth. Bacteria, especially he
Halophiles require an environment with a high concentration of _______ for optimal
growth.(CORRECT ANSWERS) salt
which of the following counting techniqes does not differenciate between live and
dead bacterial cells in a culture.(CORRECT ANSWERS) direct microscopic count.
Which of the following is most likely to have evolved in the deep layers of mud,
where there is a complete lack of free oxygen?(CORRECT ANSWERS) obligate
anaerobe
Questions and Answers
Discuss what is meant by "growth" when referring to microbes and the ways in which
it can be measured (describe the growth curve phases).(CORRECT ANSWERS)
Microbial growth is the increase in the number of cells in a culture. The increase in
number of cells occurs by cell division. This cell division usually occurs via binary
fission or budding. In binary fission, a cell duplicates its components and divides into
two separate cells. In budding, a small, new cell develops from the surface of an
existing cell and subsequently separates from the parent cell. There are four major
phases of microbial growth: 1) the lag phase. 2) The log phase. 3) The stationary
phase. 4) The decline/ death phase. The lag phase occurs when bacterium are first
transferred to a new culture. No bacterial growth occurs in the lag phase, instead the
bacterium are increasing in size, synthesizing enzymes, and absorbing nutrients
from the new medium. The length of this phase is determined by their genetics and
the condition of medium. Once the organisms have adapted to the medium, the log
phase begins. The log phase is a time of logarithmic growth (exponential growth).
During this time the organisms divide at their fastest rate. In a hypothetical situation
synchronous growth occurs. In synchronous growth, the population doubles every 20
min. However, in a real situation, some organisms take longer to go from the lag
phase to the log phase and they do not all divide at the same rate. In
nonsynchronous growth, about 1/20 or the organisms divide each minute. The time it
takes for the population to double is called generation time. When cell division
decreases to the point that new organisms are produced at the same rate organisms
are dying, the culture as reached the stationary phase. In this phase, the medium
contains a limited amount of nutrients are possibly large amounts of toxic waste. The
oxygen supply may be inadequate for aerobic organisms and damaging pH levels
may occur. The decline/ death phas
The type of cell reproduction in which small, new cells develop from the surface of an
existing cell and then separate from the parent cell is known as ____________ and
is the normal mode of replication in__________.(CORRECT ANSWERS) Budding,
yeasts.
Microbial growth(CORRECT ANSWERS) In a single generation time leads to double
the number of cells.
a bacterial culture can be kept in the log phase of growth indefinitely with the help of
a(CORRECT ANSWERS) chemostat
Which of the following bacterial counting methods relies on a statistical estimate to
determine the number of bacteria in a culture?(CORRECT ANSWERS) most
probable number
Most bacteria(CORRECT ANSWERS) do not immediately increase in number when
placed in a culture.
, Bacterial growth in colonies on agar plates______.(CORRECT ANSWERS) have all
phases of growth occurring simultaneously somewhere in the colony.
Acidophiles would be expected to growth best at a pH of(CORRECT ANSWERS) 3
Most human pathogenes are(CORRECT ANSWERS) mesophiles
Which type of cell generally shift to aerobic metabolism when oxygen is available but
will carry on fermentation otherwise.(CORRECT ANSWERS) faculative anaerobes
The toxic effects of the byproducts of oxygen metabolism are reduced by which of
the following?(CORRECT ANSWERS) catalase and superoxide dismutase.
Review the physical and nutritional factors that can influence microbial
growth.(CORRECT ANSWERS) Physical factors affecting microbial growth include
pH, temperature, quantity of oxygen, water, hydrostatic pressure, and osmotic
pressure. Microorganisms have an optimum pH- a pH at which they growth their
best. According to their tolerance of pH, bacteria are classified as acidophiles (.1-
5.4pH), neutrophiles (5.4-8.0), and alkaliphiles (7.0-11.5). Most of the disease
causing bacteria in humans are neutrophiles. Changes in pH can lead to denaturing
enzymes and other proteins and can interfere with pumping of ions through the cell
membrane. Other organisms appear to tolerate environmental acidity or alkalinity
because the cell itself is maintained at a nearly neutral pH because their cell walls
are relatively impervious so the cell wall protects the cell membrane from being
exposed to the extreme pH in the medium.
Most organisms can grow within a range of 30 degrees around their optimum
temperature. ACcording to the temperature range for growth, bacteria are classifed
as phychrophiles (cold-loving), mesophiles (room-temp), and thermophiles (heat-
loving). Obligate means that the organisms must have the specified environmental
condition. Faculative means that the organism is able to adjust and tolerate the
environmental condition but it it also able to live in other conditions. Mesophiles
include most bacteria and pretty much all human pathogens. The temperatyre range
over whch an organism grows is determined largely by the temperatures at which
enzymes function. Minimum growth rate occurs at the lowest temperature at which
cells can divide. Maximum growth rate occurs near the highest temperature at which
the cells can divide. The temperature range over which an organism grows is
determined largely by the temperatures at which enzymes function. Oxygen
concentration also effects bacterial growth. Bacteria, especially he
Halophiles require an environment with a high concentration of _______ for optimal
growth.(CORRECT ANSWERS) salt
which of the following counting techniqes does not differenciate between live and
dead bacterial cells in a culture.(CORRECT ANSWERS) direct microscopic count.
Which of the following is most likely to have evolved in the deep layers of mud,
where there is a complete lack of free oxygen?(CORRECT ANSWERS) obligate
anaerobe
