Chapter 6: Questions

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Microbial Growth: Test 2

Pathogenic bacteria are classified as _____________ for their growth temperature requirements.
a) thermophiles
b) mesophiles
c) psychrotrophs
d) halophiles
e) psychrophiles

mesophiles

An organism that you are studying grows at 4°C and at 25°C. However, it grows best at 20°C. This organism would be classified as a:
a) halophile
b) psychrophile
c) psychrotroph
d) mesophile
e) thermophile

psychrotroph

Through metabolism pathogens often produce acids that interfere with their own growth. ________ are added to media to control pH changes.
a) Growth inhibitors
b) Oxygen
c) pH indicators
d) Salts
e) Buffers

Buffers

Which of the following are mismatched?
a) Extreme halophiles : 30% salt
b) Acidophiles : low pH
c) Psychrophiles : 0°C
d) Extreme thermophiles : 100°C
e) Hyperthermophiles : no water

Hyperthermophiles : no water

Bacteria require nitrogen for the synthesis of:
a) fatty acids.
b) carbohydrates.
c) sugars.
d) lipids.
e) proteins.

proteins.

Trace elements are added to microbiological media to provide:
a) reducing agents.
b) cofactors.
c) osmotic pressure.
d) buffers.
e) energy.

cofactors.

Which of the following is not a chemical requirement of all bacteria?
a) Nitrogen
b) Mineral elements
c) Sulfur
d) Molecular oxygen
e) Carbon

Molecular oxygen

An organism that grows both in the presence and the absence of oxygen and uses oxygen when it is available is called a/an:
a) Microaerophile
b) Aerobe
c) Facultative anaerobe.
d) Anaerobe
e) Aerotolerant anaerobe.

Facultative anaerobe.

A culture medium consisting of agar, peptone and beef heart extract is a/an:
a) selective medium.
b) chemically defined medium.
c) differential medium.
d) complex medium.
e) enrichment medium.

complex medium.

Which of the following is not a component of a defined media.
a) peptone
b) Mg SO4
c) water
d) glucose
e) nitrogen

peptone

Which of the following types of media is designed to suppress the growth of unwanted bacteria and encourage the growth of desired microbes?
a) Nutrient agar
b) Selective media
c) Defined media
d) Enriched media
e) Differential media

Selective media

Niacin, when added to a medium, would be considered a/an:
a) enzyme cofactor.
b) electron carrier.
c) organic growth factor.
d) reducing agent.
e) carbon source.

organic growth factor.

Which of the following is not a step in binary fission?
a) Crosswall formation.
b) Replication of chromosomal DNA.
c) Invagination of the plasma membrane.
d) Lysis of the existing cell wall.
e) Cell elongation.

Lysis of the existing cell wall.

If a single bacterium replicated every 30 minutes, how many bacteria would be present in 2 hours?
a) 16
b) 32
c) 8
d) 4

16

In which phase of the growth curve is the population doubling time fastest?
a) Log phase.
b) Lag phase.
c) Stationary phase.
d) Logarithmic decline phase.
e) Death phase.

Log phase.

During the lag phase:
a) cells are engaged in intense enzymatic activity.
b) cells are growing in number.
c) nutrients are depleted.
d) cells are decreasing in number.
e) changes in pH occur.

cells are engaged in intense enzymatic activity.

What phase of the cell cycle is extended in a chemostat?
a) Lag phase
b) Logarithmic decline phase.
c) Log phase
d) Death phase
e) Stationary phase

Log phase

All of the following are true of the plate count method except:
a) Involves cell plating and growth.
b) Most commonly used method for assay of bacterial cell number.
c) Fast - completed in minutes.
d) Dependable.
e) Measures number of viable cells.

Fast - completed in minutes.

An unknown culture is assayed via the plate count method. After dilution of cells and incubation, no colonies are observed. Which of the following is not a possible explanation?
a) The media did not support the growth of the microbes.
b) The incubation conditions were incorrect.
c) The wrong dilution was plated.
d) The bacterial cells formed invisible colonies.
e) There were no cells in the culture.

The bacterial cells formed invisible colonies.

Blood agar used to observe hemolysis or clearing around Streptococcus pyogenes colonies is an example of a/an:
a) selective media.
b) reducing media.
c) differential media.
d) isolation media.
e) enrichment media.

differential media.

Psychrotrophic organisms are often responsible for food spoilage in refrigerated foods.
a) True
b) False

True

The addition of salts to a solution increases osmotic pressure and is used to preserve food.
a) True
b) False

True

Microaerophiles do not require oxygen for growth.
a) True
b) False

False

Aerotolerant organisms can grow in the presence of oxygen because their cell wall protects them from toxic products of oxygen.
a) True
b) False

False

Reducing media such as that containing thioglycolate may be used to grow anaerobic organisms.
a) True
b) False

True

Differential media are used to encourage growth of some bacteria while preventing the growth of others.
a) True
b) False

False

When using the spread plate technique to inoculate culture media, some colonies form within the agar.
a) True
b) False

False

In a direct microscopic count, dead cells are easily differentiated from live cells.
a) True
b) False

False

Turbidity, or cloudiness, of cell cultures measured by spectrophotometry is useful in detecting small amounts of microbial contamination in liquids.
a) True
b) False

False

Cells growing in a rich medium will have a steeper log phase slope than those growing in a nutrient poor medium.
a) True
b) False

True

Shrinking of the plasma membrane in response to osmotic loss of water is called ___________ .

plasmolysis

The ability of microbes to utilize N2 as a nitrogen source is called ______________ .

nitrogen fixation

The enzyme __________ catalyzes the conversion of peroxide to water and oxygen.

catalase

The __________ (3 words) is the most common technique used to obtain pure cultures of microbes.

streak plate method; streak plate technique

Bacteria that require increased concentrations of carbon dioxide are grown in a/an ____________ (2 words).

candle jar

An unknown organism grows at the top of a tube of thioglycollate broth. This organism is best described as a/an ___________ for its oxygen requirements.

aerobe; strict aerobe

Salt agar tends to inhibit the growth of most organisms, except Staphylococcus. This is an example of a/an ___________ media.

selective

In a/an _____________ (2 words), cells are added to melted agar and poured into a petri dish.

pour plate

When 1 ml of culture is added to 99 ml of saline in a dilution tube, the dilution achieved is ___________ .

1:100

In a pour plate technique, 32 bacterial colonies are counted on the 10-2 dilution of milk. How many bacteria were in the original milk? (Don't use scientific notation in your answer.)

3200

Which of the following organisms is an obligate anaerobe?

Clostridium (Aerobic growth -, Anaerobic growth +, Catalase -)

Which of the following organisms is an aerotolerant anaerobe?

Enterococcus (Aerobic growth +, Anaerobic growth +, Catalase -)

Which of the following organisms is a facultative anaerobe?

Salmonella (Aerobic growth +, Anaerobic growth +, Catalase +)

A medium that contains lauryl sulfate inhibits growth of gram-positive bacteria. This medium is:

selective.

S-S agar inhibits gram-positive bacteria. On this medium, bacteria that ferment lactose produce red colonies and bacteria that do not ferment lactose produce colorless colonies. This medium is:

selective & differential

You inoculate two tubes of liquid culture media with 100 bacterial cells and incubate one tube at 37° C and the other at 55° C. After 48 hours, there are 20,000 bacteria/ml in the 37° C tube and 1,568,000 bacteria/ml in the 55° C tube. You conclude that this species is a:

thermophile.

You inoculate two tubes of liquid culture media with 100 bacterial cells and incubate one tube at 15° C and the other at 35° C. After 18 hours, there are 100 bacteria/ml in the 15° C tube and 996,000 bacteria/ml in the 35° C tube. You conclude that this species is a:

mesophile.

You inoculate two tubes of liquid culture media with 100 bacterial cells and incubate one tube at 20° C and the other at 37° C. After 48 hours, there are 798,000 bacteria/ml in the 20° C tube and 2,532 bacteria/ml in the 37° C tube. You conclude that this species is a:

mesophile.

In order to look for bacteria that degrade petroleum, a culture medium containing crude oil, sodium nitrate, phosphate buffer, and magnesium sulfate is inoculated with soil. This medium is:

complex.

The following steps occur during binary fission. What is the third step?

inward growth of membrane

Bacteria that spoil food in the refrigerator are most likely:

psychrotrophs.

You inoculate a glass of milk with three mesophilic bacterial cells, and then refrigerate the milk at 7° C. How many bacterial will be in the milk after five generations?

96

If 52 bacterial colonies grow on a nutrient agar plate inoculated with one ml of a 1:1000 dilution of hamburger, how many bacteria are in the original hamburger sample?

52,000 bacteria/g

During log phase, bacteria are:

dividing at the fastest possible rate.

Assume that you inoculated potato salad with 10 bacterial cells and stored it at room temperature. After three hours there are 640 cells. How many generations did the cells go through?

6

Which of the following is the best definition of generation time?
A) The duration of log phase
B) The length of time needed for a cell to divide
C) The minimum rate of doubling
D) The time needed for nuclear division
E) The length of time needed for lag phase

The length of time needed for a cell to divide

Most bacteria grow best at pH
A) 5.
B) 14.
C) 7.
D) 1.
E) 9.

7

Which sections of a Bacterial Growth Chart illustrate a logarithmic change in cell numbers?

Log phase & Death phase

During which growth phase will gram-positive bacteria be most susceptible to penicillin?
A) Stationary phase
B) The culture is equally susceptible during all phases.
C) Death phase
D) Log phase
E) Lag phase

Log phase

A culture medium consisting of agar, peptone, and beef heart extract is a/an ________.
A) complex medium
B) chemically defined medium
C) selective medium
D) enrichment medium
E) differential medium

complex medium

Three cells with generation times of 30 minutes are inoculated into a culture medium. How many cells are there after 5 hours?
A) 1024
B) 3 x 2^10
C) 16
D) 243
E) 48

3 x 2^10

Which of the following is an advantage of the standard plate count?
A) Cannot be used to count bacteria in food
B) Determines the number of viable cells
C) Chemical and physical requirements are determined by media and incubation.
D) Requires incubation time
E) Can readily count cells that form aggregates

Determines the number of viable cells

An organism that grows both in the presence and the absence of oxygen and uses oxygen when it is available is called a/an ________.
A) aerobe
B) facultative anaerobe
C) aerotolerant anaerobe
D) microaerophile
E) anaerobe

facultative anaerobe

Most bacteria divide by which method?
A) meiosis
B) binary fission
C) mitosis
D) fusion of gametes

binary fission

Which of the following is an organic growth factor?
A) NH4H2PO4
B) H2O
C) Glucose
D) Peptone
E) NAD+

NAD+

The term facultative anaerobe refers to an organism that
A) Uses oxygen or grows without oxygen.
B) Doesn't use oxygen but tolerates it.
C) Prefers to grow without oxygen.
D) Is killed by oxygen.
E) Requires less oxygen than is present in air.

Uses oxygen or grows without oxygen.

Which enzyme catalyzes the reaction: 2H2O2 2H2O + O2?
A) Peroxidase
B) Oxidase
C) Superoxide dismutase
D) Catalase

Catalase

Salts and sugars work to preserve foods by creating a
A) Depletion of nutrients.
B) Hypotonic environment.
C) Hypertonic environment.
D) Lower osmotic pressure.
E) Lower pH.

Hypertonic environment.

During which phase of bacterial growth would you see cell dividing most rapidly?
A) stationary phase
B) death phase
C) lag phase
D) log phase

log phase

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