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If cells are grown in media containing amino acids labeled with radioactive nitrogen (¹⁵N), most of
radioactivity will be found in the cells'
A) DNA.
B) proteins.
C) phospholipids.
D) DNA and proteins.
E) DNA and phospholipids.

DNA and proteins.

Which of the following elements is NOT correctly matched with its cellular function?
A) magnesium and potassium — required as cofactors for enzymes
B) sulfur — used for synthesis of thiamin and biotin
C) nitrogen — needed for amino acid synthesis
D) phosphorus — incorporated into nucleic acids
E) None of the answers is correct; all of the elements are correctly matched.

None of the answers are correct; all of the elements are correctly matched.

Pathogenic bacteria isolated from the respiratory or intestinal tracts of humans are
A) capnophiles that grow best in carbon dioxide incubators.
B) facultative anaerobes that require reducing media for growth.
C) strict aerobes that grow best in candle jars.
D) capnophiles that prefer highly oxygenated growth conditions.
E) strict aerobes that grow best in reducing media.

Capnophiles that grow best in carbon dioxide incubators.

The biosafety level (BSL) for most introductory microbiology laboratories is
A) BSL-1. B) BSL-2.
C) BSL-3. D) BSL-4.

Biosafety Level 1

The biosafety level for a clinical microbiology laboratory working with potentially airborne pathogens, like tuberculosis bacteria, is
A) BSL-1. B) BSL-2.
C) BSL-3. D) BSL-4.

Biosafety Level 3

A sample of milk is tested for its bacterial content in a plate count assay. A one-milliliter sample of
the milk is diluted in a 1:10 dilution series. One milliliter of the third dilution tube is plated in a
pour plate. After incubation, the plate has 54 colonies, indicating that the original milk sample contained
A) 54 cells. B) 540 cells.
C) 5400 cells. D) 54,000 cells.
E) 540,000 cells.

540,000 cells.

Salts and sugars work to preserve foods by creating A) lower osmotic pressure.
B) hypotonic environment.
C) lower pH.
D) hypertonic environment.
E) depletion of nutrients.

Hypertonic Environment

The term aerotolerant anaerobe refers to an organism that
A) does not use oxygen but tolerates it.
B) uses oxygen or grows without oxygen.
C) requires less oxygen than is present in air.
D) is killed by oxygen.
E) requires more oxygen than is present in air.

Does not use oxygen but tolerates it.

Which of the following is an advantage of the standard plate count?
A) provides immediate results
B) determines the number of viable cells
C) can be used to count heat-sensitive bacteria
D) can readily count cells that form aggregates
E) can be performed on very dilute samples, such as lake water

Determines the number of viable cells.

Which of the following is an advantage of the direct microscopic count?
A) can easily distinguish live from dead cells
B) requires a large number of cells
C) sample volume is unknown
D) requires no incubation time
E) can readily count organisms that are motile

Requires no incubation time.

Most bacteria reproduce by
A) binary fission. B) fragmentation.
C) mitosis. D) aerial hyphae. E) budding.

Binary Fission.

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

pH 7 (Neutral)

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

pH 5 (Acidic)

A culture medium on which only gram-positive organisms grow and a yellow halo surrounds
Staphylococcus aureus colonies is called a(n)
A) enrichment culture.
B) selective medium.
C) differential medium.
D) selective and differential medium.
E) differential and enrichment culture.

It is a selective and differential medium.

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

Complex Medium

Which of the following pairs is mismatched?
A) hyperthermophiles — growth at 85°C
B) psychrotroph — growth at 0°C
C) psychrophile — growth at 15°C
D) thermophile — growth at 37°C
E) mesophile — growth at 25°C

Thermophile → growth at 37°C

During which growth phase will gram-positive bacteria be most susceptible to penicillin?
A) death phase
B) stationary phase
C) lag phase
D) log phase
E) The culture is equally susceptible during all phases.

Log Phase

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

The length of time needed for a cell to divide.

Which of the following is NOT a direct method to measure microbial growth?
A) direct microscopic count
B) standard plate count
C) filtration
D) most probable number (MPN)
E) metabolic activity

Metabolic Activity

Which group of microorganisms is most likely to spoil a freshwater trout preserved with salt?
A) thermophiles
B) anaerobes
C) psychrophiles
D) hyperthermophiles
E) facultative halophiles

Facultative Halophiles

Which of the following is an organic growth factor?
A) glucose
B) NH₄H₂PO₄
C) peptone
D) vitamin B1
E) H₂O

Vitamin B1

Which of the following is an example of a metabolic activity that could be used to measure
microbial growth?
A) MPN
B) standard plate count
C) glucose consumption
D) turbidity
E) direct microscopic count

Glucose Consumption

An experiment began with 4 cells and ended with 128 cells. How many generations did the
cells go through?
A) 64
B) 32
C) 6
D) 5
E) 4

5 generations.

The source of nutrients in nutrient agar is
A) agar.
B) nutrient.
C) peptone and beef extract.
D) peptone and NaCl.
E) agar and NaCl.

Peptone and beef extract.

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