chapter four: dynamics of microbial growth

If there are 10^3 cells per mL at the middle of log phase, and the generation time of the cells is 30 minutes, how many cells will there be 2 hours later? a) 2 x 10^3 b) 4 x 10^3 c) 8 x 10^3 d) 1.6 x 10^4 e) 1 x 10^7

1.6 x 10^4

The generation time of a bacterium was measured at two different temperatures. Which results would be expected of a thermophile? a) 20 minutes at 10°C; 220 minutes at 37°C b) 220 minutes at 10°C; 20 minutes at 37°C c) no growth at 10°C; 20 minutes at 37°C d) 20 minutes at 45°C; 220 minutes at 65°C e) 220 minutes at 37°C; 20 minutes at 65°C

220 minutes at 37C; 20 minutes at 65C

chemically defined medium

A culture medium made of pure chemicals so that its exact chemical composition is known; generally used only for specific experiments when nutrients must be precisely controlled.

complex medium

A culture medium that contains protein digests, extracts, or other ingredients that vary in their chemical composition.

differential medium

A culture medium with an ingredient that certain microorganisms change in a recognizable way; used to differentiate microbes based on their metabolic traits.

selective medium

A culture medium with an ingredient that inhibits the growth of microbes other than the one being sought.

pure culture

A population descended from a single cell.

obligate anaerobe

Organism that cannot multiply, and often is killed, in the presence of O2.

facultative anaerobe

Organism that grows best if O2 is available, but can also grow without it.

obligate aerobe

Organism that requires O2.

biofilm

Polymer-encased community of microorganisms.

exponential (log) phase

Stage in the growth curve during which cells divide at a constant rate; generation time is measured during this period of active multiplication.

generation time

The time it takes for a population to double in number.

binary fission

a cell increases its size and then divides asexually

growth curve

a growth pattern observed in closed systems and has five phases

which of the following is most likely to be a pure culture? a) a bacterial lawn of growth covering an agar plate b) a broth culture growing in a flask c) a single colony growing on a streak plate d) a petri dish covered with bacteria following inoculation from a single patient

a single colony growing on a streak plate

You take absorbance readings on a spectrophotometer across a 6-hour culture of E. coli cells growing in tryptic soy broth (TSB). Your absorbance readings clearly indicate a lag phase, a log phase, and a stationary phase. You come back in and take readings at 8, 10, 12, 14, and 16 hours, but the absorbance number remains the same. Shouldn't it start coming down as the closed batch culture enters death phase? What's the most likely thing that is happening? a) Something is likely wrong with the spectrophotometer and it isn't measuring the correct values. Perhaps something is on the detector, making it register falsely high absorbance numbers. b) A spectrophotometer can measure absorbance as an indicator of cell number, but can't discriminate between a live cell and a dead one. The presence of dead cells keeps the absorbance high even into the death phase. c) E. coli just grows slowly, and has a long generation time. After 16 hours the cells are still in stationary phase, so the cell numbers are expectedly constant. d) Perhaps there's a big smudge of something on the tube that is blocking some of the light. This would lead to an elevated reading for every timepoint after the smudge was placed on the tube. e) There is no point in measuring the absorbance of the culture because the cells are bacterial. It would make more sense to measure would the transmission value.

a spectrophotometer can measure absorbance as an indicator of cell number, but can't discriminate between a live cell and a dead one. the presence of dead cells keeps the absorbance high even into the death phase

which name is given to microbes that grow in environments where the pH is lower than 7? a) neutrophiles b) mesophiles c) thermophiles d) acidophiles e) alkainophiles

acidophiles

Microbes that grow readily on the bench top or in a temperature-controlled incubator that is not sealed from the atmosphere in the room are ______. a) capnophiles b) microaerophiles c) obligate anaerobes d) all pathogens e) aerobes

aerobes

which of the following organisms does not use O2 at all for growth? a) microaerophile b) aerotolerant anaerobe c) facultative anaerobe

aerotolerant anaerobe

the polysaccharide found in marine algae that is commonly used to solidify culture media is called ______. a) peptone b) starch c) agar d) gelatin

agar

if you searched around the world, where would you expect to find live prokaryotes? a) volcanic vents b) polar regions c) within animal hosts d) temperatures above boiling e) ocean depths f) all of the above g) none of the above

all of the above

which of the following are examples of growth factors? (choose all that apply) a) starch b) amino acids c) phospholipids d) cholesterol e) vitamins f) nucleotides g) polysaccharides h) water

amino acids vitamins nucleotides

a sterile medium is characterized by which of the following? a) an absence of nutrients b) an absence of viable microbes c) the lack of growing microbes

an absence of viable microbes

Which best describes the intestinal tract? a) An open system with a chemically defined medium b) An open system with a complex medium c) A closed system with a chemically defined medium d) A closed system with a complex medium

an open system with a complex medium

from which body site could a facultative anaerobe be isolated? a) surface of skin b) deep wound c) intestine d) any of these locations

any of these locations

You are setting up an enrichment culture to look for methylotrophic bacteria in a sample of water from Lake Washington in Seattle. Methylotrophs are capable of obtaining their carbon and energy needs from single carbon compounds such as methanol. In your enrichment culture, you provide methanol and a variety of macro- and micro-nutrients to encourage growth. However, which of the following must you leave out if you are to successfully enrich for methylotrophs? a) Iron b) A source of phosphorous c) Any other carbon source d) A source of nitrogen e) Potassium

any other carbon source

In the cultivation of microaerophilic and anaerobic bacteria, a) a(n) candle/anaerobe jar is sufficient. b) atmospheric oxygen in a(n) candle/anaerobe jar is converted to water. c) a packet containing chemicals that generate CO2 and hydrogen is used in a(n) candle/anaerobic jar. d) oxidizing agents are incorporated into the media that react with oxygen. e) selective and differential media must always be used.

atmospheric oxygen in a(n) candle/anaerobe jar is converted to water

in what ways is microbial growth in a colony the same as growth in a liquid? (choose all that apply) a) cells in both situations experience the same levels of nutrients b) both involve a lag phase followed by exponential growth c) cells in either situations are all in the same phase of growth at the same time d) in both cases, cells compete with one another for available nutrients

both involve a lag phase followed by exponential growth in both cases, cells compete with one another for available nutrients

ingredients that could be in complex media but not chemically defined media include which of the following? (choose all that apply) a) cell secretions b) disodium hydrogen phosphate c) blood and serum d) sodium chloride e) extracts of animals, plants, or yeasts

cell secretions blood and serum extracts of animals, plants, or yeasts

viable cell counts determine the number of ______. a) total cells (live and dead) b) cells capable of multiplying c) live cells

cells capable of multiplying

major elements

chemical elements that make up cells

culture media whose compositions are precisely defined are called which of the following? a) nonsynthetic media b) enriched media c) chemically defined media d) complex media

chemically defined media

If the pH indicator were left out of MacConkey agar, the medium would be a) complex. b) differential. c) defined. d) defined and differential. e) complex and differential.

complex

growth factors

compounds bacteria requires in its surroundings because it cannot synthesize them

enrichment culture

culture method used to isolate an organism in a mixed population

in which phase of the growth curve are more cells dying than reproducing? a) log b) stationary c) death d) lag

death

chemostat

device used to grow bacteria that allows nutrients to be added and waste to be removed

______ media support the growth of many microbes but contain substances that certain microbes change in a recognizable way.

differential

bacteria growing in a natural environment experience ______. a) dynamic and complex conditions b) conditions similar to that of the laboratory

dynamic and complex conditions

trace elements

elements required in very small amounts

Cells are most sensitive to penicillin during which phase of the growth curve? a) Lag b) Exponential c) Stationary d) Death e) More than one of these

exponential

the log phase of a normal growth curve is also referred to as the ______ phase. a) stationary b) lag c) exponential d) decline

exponential

True or False: differential media only allow certain bacteria to grow

false

True or False: freezing is an effective means of destroying bacteria

false

True or False: selective media cannot be differential

false

Microorganisms that have complicated nutritional requirements are a) heterotrophic b) fastidious c) autotrophic d) ubiquitous e) mesophiles

fastidious

bacteria that require growth factors and specific nutrients are called ______ organisms.

fastidious

which of the following are true regarding freezing? (choose all that apply) a) freezing prevents all microbial growth b) freezing is a common method used to preserve stock cultures of bacteria c) freezing is an effective means of destroying microbes d) freezing is a good method for preserving foods for long-term storage

freezing is a common method used to preserve stock cultures of bacteria freezing is a good method for preserving foods for long-term storage

what term is used to describe the amount of time a particular microbial species takes to double in number? a) generation time b) mitosis time c) growth time d) binary fission

generation time

Medically important bacteria are often a) grown on agar containing blood AND grown at 4°C. b) grown at 37°C AND grown at a pH of 5. c) grown on agar containing blood AND grown at 37°C. d) grown on agar containing chocolate AND grown at 4°C. e) grown at a pH of 5 AND grown at 4°C.

grown on agar containing blood AND grown at 37C

a graphical representation of the change in population size over time is a bacterial ______ curve.

growth

an extreme ______ specifically requires a high concentration of salt for growth.

halophile

a microorganism that has a temperature optimum close to the boiling point of water is a ______.

hyperthermophile

Trace elements a) include zinc, copper, and manganese AND may be needed for enzyme function. b) include zinc, copper, and manganese AND are required in large amounts. c) may be needed for enzyme function AND are involved in maintaining pH in the cell. d) are required in large amounts AND may be needed for enzyme function. e) are involved in maintaining pH in the cell AND include zinc, copper, and manganese.

include zinc, copper, and manganese AND may be needed for enzyme function

______ phase describes the initial phase after bacterial cells are placed into a new environment and are gearing up for cell division, but their numbers have not yet increased.

lag

E. coli, a facultative anaerobe, is grown for 24 hours on the same type of solid medium, but under two different conditions: one aerobic, the other anaerobic. The size of the colonies would be a) the same under both conditions. b) larger when grown under aerobic conditions. c) larger when grown under anaerobic conditions.

larger when grown under aerobic conditions

A soil sample is placed in liquid and the number of bacteria in the sample determined in two ways: (1) colony count and (2) direct microscopic count. How would the results compare? a) Methods 1 and 2 would give approximately the same results. b) Many more bacteria would be estimated by method 1. c) Many more bacteria would be estimated by method 2. d) Depending on the soil sample, sometimes method 1 would be higher and sometimes method 2 would be higher.

many more bacteria would be estimated by method 2

in the laboratory, a liquid or solid ______ provides nutrients for microbial growth. a) agar b) broth c) medium

medium

Compared with their growth in the laboratory, bacteria in nature generally grow a) more slowly. b) faster. c) at the same rate.

more slowly

a ______ is a microbe that prefers environments near or at a pH of 7.

neutrophile

a batch culture has which of the following characteristics? (choose all that apply) a) it is an open system b) nutrients are not renewed c) it is a closed system d) wastes are not removed e) cells are maintained in a state of continuous growth f) it typically involves growth of bacteria or archaea either on agar plates or in tubes or flasks of broth

nutrients are not renewed it is a closed system wastes are not removed it typically involves growth of bacteria or archaea either on agar plates or in tubes or flasks of broth

An enclosed compartment filled with an inert gas such as nitrogen would be most appropriate for growing ______. a) aerobes b) all pathogens c) obligate anaerobes d) microaerophiles e) capnophiles

obligate anaerobes

extremophiles

organisms living in harsh environments that would kill other organisms

Shake tubes are used to determine the a) pH requirements for bacterial growth. b) temperature requirements for bacterial growth. c) oxygen requirements for bacterial growth. d) salt requirements for bacterial growth. e) nutrient requirements for bacterial growth.

oxygen requirements for bacterial growth

some microorganisms produce acids during metabolism. which of the following would be a strong indication of this activity? a) pH of the culture medium should be lower after growth b) pH of the culture medium would remain unchanged after growth c) pH of the culture medium would be higher after growth

pH of the culture medium should be lower after growth

Anabaena is a genus of filamentous cyanobacteria commonly found in aquatic environments, where it harvests energy from sunlight and fixes both carbon dioxide and nitrogen. Knowing this, how would you classify Anabaena? a) Photoautotroph b) Photoheterotroph c) Chemolithoautotroph d) Chemoorganoheterotroph e) Chemoorganoautotroph

photoautotroph

You inoculate fern spores onto the surface of a growth medium in Petri dishes and wait for them to develop into gametophytes, a stage in the life cycle of a fern. The medium contains sources of nitrogen, phosphate, and a number of other macro- and micro-nutrients, but no carbon. After a few weeks, you see a contaminant growing on your plates. Assuming the organism is not digesting the agar itself, which of the following is most likely your contaminant? a) Photoautotrophic species of bacteria, archaea, or protists. b) Chemoorganoheterotrophic species of fungi or yeast. c) Photoautotrophic species of yeasts or fungi. d) Nitrogen fixing species of chemoorganoheterotrophic bacteria or archaea. e) Chemoorganoheterotrophic species of bacteria or archaea.

photoautotrophic species of bacteria, archaea, or protists

If the concentration of E. coli in a broth is between 10^4 and 10^6 cells per mL, the best way determine the precise number of living cells in the sample would be to a) use a counting chamber. b) plate out an appropriate dilution of the sample on nutrient agar. c) determine cell number by using a spectrophotometer. d) Any of these three methods would be satisfactory. e) None of these three methods would be satisfactory.

plate out an appropriate dilution of the sample on nutrient agar

which term describes a microorganism that has an optimal temperature between 15C and 30C, but grows well on refrigerated food? a) thermophile b) psychrotroph c) mesophile

psychrotroph

Which of the following is false? a) E. coli grows faster in nutrient broth than in glucose-salts medium. b) Organisms require nitrogen to make amino acids. c) Some eukaryotes can fix N2. d) An organism that grows on ham is halotolerant. e) Blood agar is used to detect hemolysis.

some eukaryotes can fix N2

during which phase of growth does the number of new cells balance the number of declining cells? a) death phase b) log phase c) lag phase d) stationary phase

stationary phase

a ______ medium means that the medium does not contain any viable microbes.

sterile

the method of using a sterile loop to spread a small culture sample over a medium in a pattern that gradually thins out the sample, resulting in isolated colonies, is called which of the following? a) loop dilution/pour plate method b) spread plate method c) streak plate method d) inoculation plate method

streak plate method

A physician sends a stool sample to your lab, and wants to know if there are lactose fermenting microbes in the sample. How might you determine if these microbes are present or not from this mixed-microbe specimen? a) Streak the sample for isolation on Thayer-Martin agar (which contains lactose and particular antibiotics for selectivity). b) Streak the sample for isolation on a blood agar plate (which contains lactose and red blood cells that enrich the culture for iron). c) Streak the sample for isolation on a MacConkey agar plate (which contains lactose and a pH indicator that turns pink when acid byproducts are present). d) Either Thayer-Martin agar or blood agar would work, as long as the plates are incubated in an anaerobic chamber. e) None of the answer choices would work—there's no way to reliably determine this feature from the specimen given.

streak the sample for isolation on a macconkey agar plate (which contains lactose and a pH indicator that turns pink when acid byproducts are present)

The simplest technique for isolating bacteria in growth media is referred to as the a) streak-plate method. b) pour-plate method. c) serial dilution method. d) MPN method. e) bacterial growth method.

streak-plate method

You inoculate a flask containing a complex medium with a culture of bacteria and use a spectrophotometer to measure the absorbance of the culture to detect growth. Initial measurements show a modest turbidity (cloudiness) that remains unchanged for the first few hours, followed by a steady increase for the rest of the day. Why was there this delay in growth following inoculation? a) The spectrophotometer was not sensitive enough to detect growth in the first few hours. b) A spectrophotometer is not the correct equipment to measure the turbidity of a growing culture. c) The bacteria had reached stationary phase and were entering the phase of prolonged decline. d) The bacteria were experiencing exponential growth and therefore could not be measured. e) The bacteria were actively expressing genes and synthesizing enzymes in order to grow in their new environment.

the bacteria were actively expressing genes and synthesizing enzymes in order to grow in their new environment

You are culturing a new bacterium in the laboratory. You cannot find any glucose it the lab when you are making growth medium, so you decide to use honey instead. You add twice as much honey than is called for in the medium recipe, because you want to give the organism the best opportunity or growth. To your surprise, the organism does not grow on your modified medium. Select the most likely explanation. a) The growth medium became hypotonic with the addition of so much honey; the bacteria underwent plasmolysis and died. b) The growth medium became hypertonic with the addition of so much honey; the bacteria underwent plasmolysis and died. c) The growth medium became halophilic with the addition of so much honey; the bacteria underwent plasmolysis and died. d) The growth medium became hypertonic with the addition of so much honey; the bacteria underwent osmotic lysis and died. e) The growth medium became hypotonic with the addition of so much honey; the bacteria underwent simple diffusion and burst.

the growth medium became hypertonic with the addition of so much honey; the bacteria underwent plasmolysis and died

which of the following correctly describe facultative anaerobes? (choose all that apply) a) they can only grow in the absence of O2 b) their growth is faster when O2 is available c) they can grow in the presence of O2 but do not use it to harvest energy d) they can grow without O2

their growth is faster when O2 is available they can grow without O2

microorganisms with an optimum temperature between 45C and 70C, commonly found in hot springs and compost heaps, are ______. a) psychrophiles b) thermophiles c) psychrotrophs d) mesophiles

thermophiles

how are liquid batch cultures most often aerated to support the growth of aerobic microbes? a) they are grown in tubes or flasks that are shaken continuously b) air is pumped into the tubes or flasks to supply sufficient O2 c) pure O2 flows under pressure from a gas cylinder into the tubes or flasks to supply maximum O2

they are grown in tubes or flasks that are shaken continuously

how do high levels of salt or sugar work to preserve food? a) they reduce water availability, making it difficult for food spoilage microbes to grow b) they create a hypotonic environment that leads to plasmolysis of bacterial cells c) they encourage growth of beneficial microbes, which outcompete food spoilage microbes

they reduce water availability, making it difficult for food spoilage microbes to grow

a direct cell count determines the number of ______ in a sample a) dead cells only b) total cells c) live cells only

total cells

True or False: a pure colony is a distinct mass of microorganisms which develop from a single cell growing on a solid medium.

true

True or False: it is sometimes difficult to obtain pure cultures of microbes that grow naturally in mixed communities

true

True or False: many medically important bacteria grow best in aerobic atmospheres that have additional CO2

true

True or False: microbes will only grow until the least represented (limiting) nutrient is used up.

true

True or False: the spread-plate technique uses a sterile tool, such as an L-shaped glass rod, to distribute the sample evenly around the surface of a plate.

true

based on your understanding of the microbial world, which of the following would you anticipate would need phosphorus? (choose all that apply) a) prions b) viruses c) bacteria d) viroids e) helminths

viruses bacteria viroids helminths

consider the following environmental factors. which have the most impact on microbial growth? (choose all that apply) a) water availability b) temperature c) wind speed d) odor e) oxygen availability f) pH

water availability temperature oxygen availability pH

Phosphate is typically a limiting nutrient in waterways. Phosphate was historically widely used in detergents, but because wastewater treatment plants do not fully remove phosphate before discharging their treated water, it has been mostly removed from these detergents in order to protect our waterways. Some complain that modern detergents do not clean as well following this change. Predict what would happen if phosphate was returned to detergents. a) Phosphate would make it difficult for microorganisms to grow, leading to lifeless waterways. b) Phosphate would increase the growth rate of fish, leading to overpopulation in our waterways. c) We would experience blooms of cyanobacteria and algae in our waterways. d) There would be phosphate poisoning in the rivers that would kill off fish. e) As a limiting nutrient, phosphate would prevent the growth of cyanobacteria and algae.

we would experience blooms of cyanobacteria and algae in our waterways

Following the Exxon Valdez oil spill, beaches in Prince William Sound were treated with nitrogen compounds in order to enhance the bioremediation of the oil. What does this tell you about the ecosystem of these beaches? a) With the arrival of large quantities of nitrogen, carbon was a limiting nutrient for microbial growth. b) With the arrival of large quantities of hydrocarbons, phosphorous was a limiting nutrient for microbial growth. c) Microorganisms are unable to grow on the abundant hydrocarbons found in oil. d) With the arrival of large quantities of hydrocarbons, nitrogen was a limiting nutrient for microbial growth. e) Nitrogen was used to react with the hydrocarbons of oil in order to enhance its degradation.

with the arrival of large quantities of hydrocarbons, nitrogen was a limiting nutrient for microbial growth