Deck 5: Microbial Growth and Control

Question 1

What temperature is most commonly used for autoclaves to sterilize growth media and other devices prior to experimentation?

A)95°C
B)101°C
C)121°C
D)140°C

Answer 1

C

Question 2

Optical density and viable cell concentration are LEAST proportional to each other during

A)lag phase.
B)exponential growth phase.
C)stationary phase.
D)death phase.

Answer 2

D

Question 3

The time interval required for the formation of two cells from one is called the

A)generation time.
B)growth time.
C)growth rate.
D)division rate.

Answer 3

A

Question 4

Enumerating cells in a biofilm is especially challenging for

A)microscopic direct counting.
B)measuring turbidity.
C)viability counts with spread plating.
D)microscopic direct county,measuring turbidity,and viability counts with spread plating.

Question 5

Most mesophilic organisms can grow in a temperature range of

A)0-15°C.
B)10-20°C.
C)20-40°C.
D)50-65°C.

Question 6

The time between inoculation and the beginning of growth is usually called the

A)lag phase.
B)log phase.
C)dormant phase.
D)death phase.

Question 7

Cell density in a chemostat is controlled by

A)the concentration of the limiting nutrient.
B)the dilution factor.
C)the size of the initial inoculum.
D)the concentration of the limiting nutrient,the dilution factor,and the size of the initial inoculum.

Question 8

An agar plate for counting colonies and maximizing statistical validity should ideally contain

A)1 to 100 colonies.
B)50 to 100 colonies.
C)30 to 300 colonies.
D)100 to 1000 colonies.

Question 9

Relative to enzymes in mesophilic microorganisms,which of the following is NOT characteristic of enzymes in psychrophiles?

A)decreased alpha helices
B)decreased beta sheets
C)less hydrogen bonds
D)less ionic bonds

Question 10

Where would it be best to isolate bacteria from to study the mechanism of the sodium motive force?

A)human gut
B)hot springs
C)soda lakes
D)volcanoes

Question 11

To determine viable cell counts of a heat-sensitive bacterial isolate,which cell counting method would be best to AVOID?

A)spread-plate method
B)pour-plate method
C)live staining and direct counting with a microscope
D)both spread- and pour-plate methods

Question 12

Which of the following is/are transferred to daughter cells during cell division?

A)genomic DNA,the blueprint for everything the cell needs
B)individual genes and enzymes to later be brought together to form the genome
C)chromosome and enzymes to immediately begin cellular metabolism
D)chromosome,proteins,and all other cellular constituents

Question 13

The MOST effective antibiotics in preventing growth of disease-causing bacteria are

A)bacteriocidal.
B)bacteriostatic.
C)bacteriolytic.
D)bacteriolytic or bacteriocidal.

Question 14

The process by which two cells arise from one is known as

A)conjugation.
B)binary fission.
C)meiosis.
D)mitosis.

Question 15

Which is most abundant and active in divisome complexes?

A)FtsZ
B)DNA replication forks
C)MinCD
D)MreB

Question 16

The number of colonies obtained in a plate count does NOT depend on the

A)inoculum volume.
B)size of the colonies.
C)type of culture medium.
D)incubation time.

Question 17

The addition of thioglycylate into a growth medium would NOT support the growth of a(n)

A)aerotolerant anaerobe.
B)facultative aerobe.
C)microaerophilic aerobe.
D)obligate anaerobe.

Question 18

Many aromatic compounds used for growth substrates by bacteria are broken down during high heat autoclaving.Which is the BEST way to sterilize these aqueous solutions?

A)ethylene oxide gas treatment
B)gamma irradiation
C)0)2 μm filter sterilization
D)ultraviolet radiation

Question 19

Bacteria that are able to grow in humans and cause disease have likely evolved to be

A)psychrophiles.
B)mesophiles.
C)thermophiles.
D)hyperthermophiles.

Question 20

A bacterium that lacks the mreB gene will have a ________ shape.

A)bacillus
B)coccoid
C)short bacillus
D)vibrio

Question 21

In general,which group is MOST resistant to radiation?

A)microscopic fungi
B)viruses
C)thermotolerant bacteria
D)spore-forming bacteria

Question 22

The partition that is a result of the inward growth of the cytoplasmic membrane and cell wall from opposing directions is known as the

A)divisome.
B)septum.
C)autolysin.
D)colony.

Question 23

Organisms able to live in environments with high sugar concentrations are

A)halotolerant.
B)osmophiles.
C)xerophiles.
D)anaerobic fermenting bacteria.

Question 24

Which term is most relevant in describing the efficacy of an antimicrobial for use in a clinical setting?

A)effective dose
B)sterilization coefficient
C)lethal dosage
D)minimum inhibitory concentration

Question 25

Which of the following methods to enumerate cells often requires specialized staining to observe non-pigmented bacteria?

A)spectrophotometry/turbidity
B)spread-plating
C)microscopy
D)spread-plating,turbidity,and microscopy

Question 26

Which of these statements is/are TRUE?

A)In general,prokaryotic organisms can grow at higher temperatures than eukaryotic organisms.
B)The most thermophilic prokaryotes are species of Archaea.
C)Nonphototrophic organisms are able to grow at higher temperatures than phototrophic organisms.
D)All of the statements are true.

Question 27

A bacterium containing ________ provided with hydrogen peroxide will produce oxygen bubbles.

A)catalase
B)superoxide dismutase
C)superoxide reductase
D)peroxidase

Question 28

When water activity is low,an organism must

A)increase its internal solute concentration.
B)increase its external solute concentration.
C)decrease its internal solute concentration.
D)decrease its external solute concentration.

Question 29

A halotolerant facultative anaerobic bacterium would grow BEST in a ________ environment.

A)oxygen depleted saline
B)oxygenated saline
C)oxygen depleted non-saline
D)oxygenated non-saline

Question 30

An antibiotic that increased the activity of ________ would likely result in cell death.

A)autolysin
B)binary fission
C)stationary growth
D)ionic bonds in proteins

Question 31

A microbe growing in a refrigerator is likely

A)psychrophilic.
B)mesophilic.
C)psychrotolerant or psychrophilic.
D)hyperthermophilic.

Question 32

A chemical that denatures proteins is MOST likely to be classified as a(n)________ agent.

A)antiseptic
B)bacteriostatic
C)bacteriocidal
D)detergent

Question 33

Consider solution A (pH 6)and solution B (pH 9).Which of the following statements is CORRECT?

A)Solution A is 3 times more acidic than solution B.
B)Solution A is 300 times more acidic than solution B.
C)Solution B is 1,000 times more alkaline (basic)than solution A.
D)Solution B is 3,000 times more alkaline (basic)than solution A.

Question 34

Superoxide dismutase and catalase work together to convert superoxide into

A)peroxide.
B)oxygen.
C)ozone.
D)water.

Question 35

What is the function of bactoprenol?

A)It is a hydrophobic alcohol that transports peptidoglycan precursors across the cytoplasmic membrane.
B)It is responsible for forming the peptide cross-links between muramic acid residues in adjacent glycan chains.
C)It triggers the recruitment of FtsZ and the initiation of the divisome.
D)It supplies the energy necessary for transpeptidation to occur.

Question 36

By controlling the concentration of nutrients added into a chemostat continuously,cells can constantly be maintained at

A)exponential growth phase.
B)stationary growth phase.
C)log or stationary growth phase.
D)death growth phase.

Question 37

Which method would be LEAST effective at sterilizing a glass hockey stick to use in the spread-plate method?

A)autoclaving
B)gamma radiation
C)ethanol soaking
D)ultrahigh-temperature pasteurization

Question 38

The ratio of the vapor pressure of the air in equilibrium with a substance to the vapor pressure of pure water is known as

A)water activity.
B)vapor activity.
C)positive water balance.
D)osmosis.

Question 39

Which of the following forms of oxygen is/are generally toxic to living organisms?

A)superoxide anion
B)hydrogen peroxide
C)hydroxyl radical
D)superoxide,hydrogen peroxide,and hydroxyl radicals are all toxic

Question 40

To determine the specific growth rate of a bacterial population,it is essential to know

A)cell concentrations at varied time points.
B)total number of cells in the population at varied time points.
C)cell concentrations at varied time points or the generation time.
D)turbidity measurements and the total number of cells in the population at varied time points.

Question 41

By using a stain targeting living cells only,microscopy would be a better approach to enumerate the number of living cells in a soil sample compared to viability counts of serially diluted soil.

Question 42

In a chemostat,growth rate and growth yield can be controlled independently.

Question 43

Direct microscope counting of stained cells is an accurate method for calculating the exact number of cells in a sample.

Question 44

In fast-growing Escherichia coli cells,multiple replication forks of genomic DNA allows binary fission to occur before the genome has been fully duplicated.

Question 45

The death phase applies to individual cells rather than populations.

Question 46

Counting chambers are used for estimating the number of cells present in a liquid culture.

Question 47

Generation of new bacillus-shaped cells starts with one cell elongating and terminates when split into two separate bacilli.

Question 48

The rates of exponential growth (in the exponential phase)vary greatly according to the bacterial species as well as the bioavailable nutrients.

Question 49

The duration of logarithmic growth would increase if bacterial cells divided into three equal daughter cells rather than two.

Question 50

When viable cell concentrations are too high to count on an agar medium,it is most common to use larger sized plates to increase the surface area for counting the colonies.

Question 51

Growing bacteria that degrade an environmental pollutant,which is also toxic to the cells at artificially high concentrations,might require ________ to obtain a sufficient population for biochemistry studies.

A)a continuous batch culture
B)a second growth substrate to keep the culture in exponential growth phase
C)steady state growth kinetics
D)the use of a chemostat

Question 52

The lag phase does NOT occur if all the cells in the culture are viable.

Question 53

An antiseptic (or germicide)is distinguished from other sterilizing compounds by

A)being able to inhibit growth of microorganisms but not necessarily kill all of them.
B)being able to be used on living tissues without harm.
C)its ability to protect from subsequent microbial infections-not just initial sterilization.
D)killing all bacteria and microscopic fungi but not being effective against viruses.

Question 54

A drug targeting ________ would NOT be an effective antibiotic.

A)ZipA
B)FtsI
C)MreB
D)transpeptidation

Question 55

The activity of MinC and MinD direct whether a bacterial cell will be coccoid or bacillus shaped.

Question 56

One laboratory group repeated the same experiment described by others with the identical bacterial isolate and the same growth medium and conditions used but were unable to achieve the same O.D.at 600 nm.What is the LEAST likely cause for this discrepancy of turbidity measured?

A)One lab used 16 mm wide test tubes and the other used 18 mm wide test tubes.
B)One lab subtracted the yellow color of the growth medium away from the final turbidity reported whereas the other lab used colorless water.
C)One lab vigorously dispersed the biofilm-forming bacteria with vortexing and the other did not.
D)The two labs varied with 1000 m elevation and did not consider the influence of pressure.

Question 57

Microbial growth is generally described as the increased number of cells rather than the expanding size of an individual microbial cell.

Question 58

Heterotrophic bacteria will run out of organic growth substrates in batch cultures but chemostats can provide constant nutrient source for them to grow.Chemostats for photoautotrophic bacteria are not necessary to maintain them at a constant growth phase because a light can artificially be turned on constantly.

Question 59

For most purposes of studying bacterial isolates,viable counting usually gives accurate information about the number of active cells present in a culture volume.

Question 60

In both lag and stationary phase,there is no net increase or decrease in viable cells.

Question 61

In principle,the chemical composition of membranes in obligate acidophiles could be distinguished from neutrophiles.

Question 62

The optimum temperature is usually closer to the minimum temperature than the maximum temperature.

Question 63

Knowing the concentration of microorganisms in a sample is often an important consideration for environmental,industrial,and medical microbiologists,yet a microscope is sometimes not used to accomplish this task.Explain five major limitations to using a light microscope to directly count microorganisms.

Question 64

Some microbes can grow in boiling water.

Question 65

Use the formulas N = N₀2ⁿ and g = t/n.
N = final cell number,N₀ = initial cell number,
n = number of generations,t = time,g = generation time.
Find the generation time if N = 2 × 10⁸,N₀ = 3 × 10⁶ and t = 3 hours.

Question 66

One reason food is refrigerated to control microbial growth is because irreversible cell damage is more likely to occur at low rather than high temperatures.

Question 67

Explain the difference between the division rate and the generation time.

Question 68

A bacterium's pH optimum reflects the optimal pH of its intracellular environment.

Question 69

Taq polymerase was isolated from a thermophile and is used in the polymerase chain reaction (PCR)technique because it does not become inactivated at high temperatures.

Question 70

The sensitivity of DNA and RNA is one major reason water activity can limit microbial growth.

Question 71

Due to the relationship between the rate of enzyme catalysis and temperature,organisms living in boiling hot springs are also rapid growers with fast doubling times.

Question 72

Identifying bactoprenol inside the rare bacteria that lack peptidoglycan would be unexpected considering its role in membrane biosynthesis.

Question 73

A non-aerated or shaken liquid growth medium inoculated with a bacterium is one of the best ways to culture an obligate anaerobe.

Question 74

Compare and contrast the spread plate method and the pour plate method of doing plate counts.Also describe which group of organisms would not be quantifiable in the pour plate method but would still be observed in the spread plate method.

Question 75

Sterility of a laminar flow hood is accomplished by filter-sterilized air passed through the hood quickly enough that non-sterile air does not flow into the work area.

Question 76

Explain why a hyperthermophile is unlikely to be a human pathogen.

Question 77

A bacterium such as a snow alga that is able to survive a cold temperature is called a psychrophile.

Question 78

Enumerating the viable and total cell concentration of a population of a microbial isolate can be a really laborious task for a microbiologist.Especially when a microbiologist studies the same isolate for several years,it often becomes practical to determine the relationship between optical density (OD)and cell concentration.Once this relationship (determined by a standard curve)is determined,the OD of an isolate in a broth can be routinely used to determine the population's concentration.Why must a standard curve be prepared for each isolate when using OD measurements to determine cell concentration? Also describe an experiment that would generate this type of standard curve.

Question 79

An unpressurized autoclave would not be able to sterilize a growth medium with contaminating bacteria but could still pasteurize it.

Question 80

During elongation of a cell during binary fission,small gaps caused by transglycosylases are formed before cell membrane precursors can be inserted.