Microbiology Chapter 4
True or false: A direct cell count typically determines only the number of live cells in a sample.
False A direct cell count generally does not distinguish between live and dead cells.
What term is used to describe essential organic compounds, such as a vitamin or amino acid, that must be provided in the diet?
Growth factors
Which type of organism requires organic compounds for its carbon and energy needs?
Heterotroph
Some species of microorganisms can be found in environments where no unprotected human could survive. true or false
True
True or false: A colony is a distinct mass of microorganisms which develop from a single cell growing on a solid medium.
True
______ describes the cloudiness or haziness of a fluid.
Turbidity
Some microorganisms live in harsh environments that kill most other organisms. The term used to describe an organism with this characteristic is----
extremophile or extremophiles
Some microorganisms live in harsh environments that kill most other organisms. The term used to describe an organism with this characteristic is
extremophiles
According to the figure, food stored for one to two hours at a temperature of 32 degrees Celsius would be safe to eat. true/false
false
Both human cells and bacterial cells divide by mitosis. true or false
false
Cell division is triggered exclusively when cells attain a threshold mass. true or false
false
DNA helicase is responsible for adding nucleotides to the growing end of the DNA. true/false
false
A -----factor is an organic compound, such as a vitamin or an amino acid, that a given microorganism cannot synthesize and therefore must be provided in the growth medium.
growth
A---factor is an organic compound, such as a vitamin or an amino acid, that a given microorganism cannot synthesize and therefore must be provided in the growth medium.
growth
A graphical representation of a changing population size over time is called which of the following?
growth curve
An organism that must consume organic matter is called a(n)
heterotroph,
An organism that must consume organic matter is called a(n)
heterotroph, chemoheterotroph, chemoorganoheterotroph, chemoorganotroph, organotroph, or chemotroph
A(n)--- aerobe, or strictly aerobic organism, requires O2 for survival.
obligate
A species grows most rapidly at its ___ growth temperature.
optimum, optimal, or ideal
Some microorganisms produce acids during metabolism. Which of the following would be a strong indication of this activity?
pH of the culture medium should be lower after growth
An autotrophic organism that uses light for energy and carbon dioxide as a carbon source is termed a-----
photoautotroph
An organism that gets its energy directly from sunlight is called a(n)
phototroph or photoautotroph
If the solute concentration is higher outside the cell than inside the cell, water will diffuse out due to osmosis. This will result in
plasmolysis
Microbial cells must maintain a near-neutral internal pH. Because of this, bacteria that grow in acidic environments have mechanisms to ______.
pump out H+ that enter the cell
A----culture contains only ONE species of microorganisms descended from a single cell.
pure
A medium that contains an ingredient that inhibits the growth of some bacteria, while allowing others to grow, is called a(n)---- medium.
seletive
The FtsZ protein is needed to form the ____
septum
The FtsZ protein is needed to form the _____.
septum
A photoautotroph obtains energy from ______ and carbon from ______ in order to make organic compounds.
sunlight; CO2
The environmental factor that influences bacterial growth the most is
temperature Correct
The safe temperature ranges for the storage of foods are determined by
the low temperature at which microbes stop multiplying and the high temperature at which they die. Correct
A direct cell count determines the number of ______ in a sample
total cells
The type of food-borne infection known as an intoxication is caused by
toxins produced by microbes as they grow in the food
The type of food-borne infection known as an intoxication is caused by
toxins produced by microbes as they grow in the food.
Bacteria may be involved in both the production or food and in its decay. true or false
true
Environmental factors control microbial growth through their effect on enzyme activity. true/false
true
Some species of microorganisms can be found in environments where no unprotected human could survive. true or false
true
The term that describes the appearance of a cloudy broth culture is
turbidity
If you want to determine the proportion of cells that have been killed by a particular antimicrobial treatment, it would be best to do which type of cell count before and after that treatment?
viable cell count
Consider the following environmental factors. Which have the most impact on microbial growth?
water availability oxygen availability pH temperature
Which of the following environmental factors is the most important in influencing the growth rate of bacteria?
Temperature
Which of the following environmental factors is the most important in influencing the growth rate of bacteria?
Temperature Correct
Which is the best definition of generation time?
The time it takes for the number of cells in a population to double.
Imagine you are a microbiologist trying to isolate new species of prokaryotes. You collect numerous samples and return to your lab, where you proceed to encourage any prokaryotes present to grow. Disappointingly, you are not successful. Which is the LEAST likely explanation for this outcome?
There were no prokaryotes present where you sampled.
Which describes the various laboratory media used to cultivate bacteria?
They are diverse in nutrient content and consistency.
How are liquid batch cultures most often aerated to support the growth of aerobic microbes?
They are grown in tubes or flasks that are shaken continuously.
According to the graph, what is the impact of cold temperatures on E. coli?
As temperatures decrease, the growth rate decreases.
Starting from a single bacterium, after six generations of binary fission, how many bacterial cells will be present?
64
Which of the following is most likely to be a pure culture?
A single colony growing on a streak plate.
What term is used to describe organisms that use CO2 as a carbon source?
Autotrophs
What term is used to describe a group of microbes co-existing in polymer-encased communities?
Biofilm
When bacteria or archaea are grown on agar plates or in tubes or flasks of broth, these closed systems are a -----culture. By contrast, cells can also be grown in an open system, or a continuous culture.
Blank 1: batch
A continuous culture system that adds nutrients and removes waste in order to maintain a constant growth rate and cell density is called a------ .
Blank 1: chemostat or bioreactor
The characteristic pattern that shows the changes in size of a bacterial population over time in a broth culture is called a bacterial---- -----
Blank 1: growth Blank 2: curve
Regardless of the pH of the external environment, microbial cells maintain a constant internal pH, typically near neutral. For example, prokaryotes that grow in alkaline conditions bring in -----into the cell.
Blank 1: protons or H+
In what ways is microbial growth in a colony the same as growth in a liquid?
Both involve a lag phase followed by exponential growth. In both cases, cells compete with one another for available nutrients.
Which of the following best describes how the atmospheric needs of aerobic microbes can be met?
By growing them in the air.
You are setting up an enrichment culture to look for bacteria that can use phenol as a carbon source. In your medium, you provide a variety of major elements and trace elements, plus phenol. Other than that contained in the phenol, what must you avoid adding if you hope to enrich for phenol-degraders?
Carbon
What happens to bacterial cells when their maximum growth temperature is exceeded?
Cells begin to die when their maximum growth temperature is exceeded.
Why are cells growing in a colony on solid media likely to be in many more different phases of growth than cells growing in liquid culture?
Cells in liquid culture experience a relatively uniform environment, so they are much more likely to be in the same phase of growth. Unlike cells on the edge of a colony, those in the center of a colony face depleted levels of nutrients and O2, yielding different phases of growth.
Which device is used to keep cells in a state of constant growth?
Chemostat
According to the figure, food stored for one to two hours at a temperature of 32 degrees Celsius would be safe to eat. true/false
False
Which of the following does not describe interactions of mixed microbial communities?
Conditions in mixed microbial associations are readily reproduced in the laboratory.
True or false: A direct cell count typically determines only the number of live cells in a sample.
False
In what ways is microbial growth in a colony the same as growth in a liquid?
In both cases, cells compete with one another for available nutrients. Both involve a lag phase followed by exponential growth.
Which of the following describe selective media?
Inhibit the growth of certain species Allow the growth of desired organisms
A batch culture has which of the following characteristics?
It is a closed system. It typically involves growth of bacteria or archaea either on agar plates or in tubes or flasks of broths. Nutrients are not renewed. Wastes are not removed.
Which of the following describes the optimum temperature of a psychrophile relative to a thermophile?
It is lower than a thermophile.
Which is the best general description of a medium used to support bacterial growth in a Petri dish?
It may have very few nutrients, or it may have many different nutrients to support widely varying growth requirements.
Which of the following describes a microbe that must have O2 to survive?
Obligate aerobe
Which term is used to describe organisms that can obtain energy directly from sunlight?
Phototrophs
Which environment is more dynamic and complex?
Soil and its surroundings
Why are cells growing in a colony on solid media likely to be in many more different phases of growth than cells growing in liquid culture?
Unlike cells on the edge of a colony, those in the center of a colony face depleted levels of nutrients and O2, yielding different phases of growth. Cells in liquid culture experience a relatively uniform environment, so they are much more likely to be in the same phase of growth.
How might an enrichment culture be used to isolate organisms capable of nitrogen fixation?
Using a media that does not contain any form of nitrogen, and exposing it to the atmosphere
A batch culture has which of the following characteristics?
Wastes are not removed. Nutrients are not renewed. It is a closed system. It typically involves growth of bacteria or archaea either on agar plates or in tubes or flasks of broths.
A single species of bacteria grows best at
a modest range around an optimum temperature
A single species of bacteria grows best at
a modest range around an optimum temperature.
If O2 is present in an environment, it is said to be _______.
aerobic
An environment with little or no O2 present is called a(n)--- environment.
anaerobic
A(n) ---requires only carbon dioxide as a sole carbon source.
autotroph, chemolithoautotroph, chemoautotroph, chemolithotroph, or photoautotroph
The most common organisms causing food spoilage are
bacteria, yeasts, and molds.
When bacteria or archaea are grown on agar plates or in tubes or flasks of broth, these closed systems are a---culture. By contrast, cells can also be grown in an open system, or a continuous culture.
batch
The presence of microbes in food can be ______.
beneficial, harmful, or neutral Correct
Bacteria and archaea typically divide by a process known as
binary fission
Many bacterial communities secrete polysaccharides and other hydrophilic polymers. This mesh-like accumulation can help protect the bacteria growing within from antibiotics or disinfectants. These communities are called
biofilms
Bacteria growing in a natural environment experience ______.
dynamic and complex conditions
If conditions are favorable, the generation time of bacteria
can be as short as 30 minutes.
Viable cell counts determine the number of ______.
cells capable of multiplying
An isolated----is a distinct mass of microorganisms appearing on a solid medium, arising from the multiplication of a single cell.
colony
In order to detect bacteria growing in patient blood samples, clinical labs can use a fluorescent sensor to detect the slight ______ in pH that accompanies the production of carbon dioxide.
decrease
By keeping food cold, the growth rate of food spoilage microorganisms is
decreased
