Microbiology Chapter 4

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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


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