Deck 5: Environmental Influences and Control of Microbial Growth

Question 1

Most bacteria require water activity to be greater than

A) 0.10.
B) 0.25.
C) 0.74.
D) 0.91.
E) 1.0.

Answer 1

D

Question 2

Which of the following enzymes are stable in part because they contain relatively low amounts of the small amino acid glycine?

A) psychrophilic
B) acidophilic
C) thermophilic
D) halophilic
E) barophilic

Answer 2

C

Question 3

Which of the following are prominent members of microbial communities beneath icebergs in the Arctic and Antarctic?

A) barophiles
B) psychrophiles
C) mesophiles
D) thermophiles
E) acidophiles

Answer 3

B

Question 4

The fastest growth rate for a species occurs at temperatures where a cell's ________ work most efficiently.

A) lipids
B) membranes
C) nucleic acids
D) proteins
E) polysaccharides

Question 5

Which temperature is lethal to any mesophile?

A) its optimum growth temperature
B) its minimum growth temperature
C) its maximum growth temperature
D) refrigeration temperature
E) autoclave temperature

Question 6

Which of the following grows in the indicated pH range shown in the figure below?

A) psychrophiles
B) mesophiles
C) piezophiles
D) alkaliphiles
E) acidophiles

Question 7

Psychrophiles favor the cold, since their membranes are more fluid at low temperature as a result of the high proportion of ________ present.

A) saturated fatty acids
B) unsaturated fatty acids
C) lipopolysaccharides
D) transport proteins
E) water

Question 8

Which of the following have evolved to grow in conditions extremely different from those optimal for humans?

A) psychrophiles
B) extremophiles
C) halophiles
D) thermophiles
E) acidophiles

Question 9

All of the following are true about microbes and temperature EXCEPT

A) microbes have mechanisms to control their temperature.
B) temperature affects the average rate of molecular motion.
C) changes in temperature affect membrane fluidity.
D) changes in temperature affect transport.
E) every organism has an optimum temperature for growth.

Question 10

The membrane needs to remain ________ so that it can expand as cells grow larger and so that proteins needed for solute transport can be inserted into the membrane.

A) rigid
B) warm
C) fluid
D) hypertonic
E) polarized

Question 11

Which of the following is NOT true about thermophiles?

A) Their proteins contain less glycine.
B) They have more unsaturated linear lipids in their membranes.
C) They have chaperone proteins.
D) Their genomes are packed with numerous DNA-binding proteins that stabilize DNA.
E) They have special enzymes that function to tightly coil DNA.

Question 12

Organisms adapted to grow at overwhelmingly high pressures are called

A) psychrophiles.
B) thermophiles.
C) barophiles.
D) acidophiles.
E) mesophiles.

Question 13

The general result of the Arrhenius equation is that growth rate roughly doubles for every ________°C rise in temperature.

A) 5
B) 10
C) 15
D) 20
E) 25

Question 14

One function of programmed cell death is to

A) increase the pH of the local environment.
B) release antibiotic resistance compounds.
C) increase the solute concentration of a hypotonic solution.
D) decrease the pH of the local environment.
E) release nutrients that neighboring cells use to survive.

Question 15

Organisms that grow at temperatures as high as 121°C as well as high pressure are known as

A) thermophiles.
B) extreme halophiles.
C) psychrophiles.
D) hyperpsychrophiles.
E) hyperthermophiles.

Question 16

Which of the conditions can be labeled as "extreme"?

A) near-neutral pH
B) 25°C
C) pressure of 400 atm
D) a salt concentration of 0.9%
E) pressure of 14 psi

Question 17

At the bottom of the ocean, hydrostatic pressure averages a crushing 400 atm (atmospheres) and can go as high as ________ atm.

A) 700
B) 1,000
C) 1,500
D) 3,000
E) 3,500

Question 18

Cyanobacterial blooms such as those shown in the figure below are typically due to human-caused

A) antibiotic resistance.
B) warming.
C) oxygenation.
D) salinity increase.
E) eutrophication.

Question 19

A measure of the number of solute molecules in solution and is inversely related to water activity is known as

A) osmolarity.
B) hypertonic.
C) hypotonic.
D) isotonic.
E) d-value.

Question 20

Human pathogens are

A) halophilic.
B) psychrophilic.
C) mesophilic.
D) thermophilic.
E) extreme thermophilic.

Question 21

Which of the following is an important signaling molecule that controls global gene expression during starvation?

A) cyclic AMP
B) ADP
C) ATP
D) glucose
E) water

Question 22

A bacterium that thrives in your stomach is probably a(n)

A) thermophile.
B) neutrophile.
C) alkaliphile.
D) acidophile.
E) psychrophile.

Question 23

An organism that grows in the circled region of the tube of medium containing thioglycolate shown below is probably a(n)

A) strict aerobe.
B) facultative anaerobe.
C) aerotolerant anaerobe.
D) microaerophile.
E) strict anaerobe.

Question 24

Which best describes microaerophiles?

A) They require atmospheric oxygen levels to grow.
B) They cannot grow in the presence of oxygen.
C) They will use oxygen if it is present, but can grow even if oxygen is not present.
D) They require a small oxygen concentration to grow.
E) They can't use oxygen to grow, but oxygen won't kill them.

Question 25

Microbes accumulate ________ in the cell to prevent cell water loss in a hypertonic environment.

A) water
B) proteins
C) sugars
D) protons
E) compatible solutes

Question 26

Which of the following is true of microbes and their membranes?

A) They are relatively permeable to protons.
B) Protons can leak through directly when the difference in intracellular and extracellular pH is very high.
C) Membrane-permeant organic acids can prevent the leakage of protons.
D) They are able to change the pH optima of their enzymes.
E) Acidophiles use Na+/H+ antiporters to remove internal protons.

Question 27

An organism that requires atmospheric oxygen levels for growth is

A) aerobic.
B) microaerophilic.
C) aerotolerant.
D) anaerobic.
E) facultative.

Question 28

The use of oxygen as the terminal electron acceptor is called

A) aerobic respiration.
B) anaerobic respiration.
C) fermentation.
D) oxygenic photosynthesis.
E) carbon dioxide fixation.

Question 29

What is depicted in the following figure?

A) Antibiotic production has inhibited bacterial growth.
B) A bacteriophage has preyed on the bacterial colonies.
C) Weak acid production has inhibited bacterial growth.
D) A biofilm has become resistant to disinfectants.
E) Starving cells have undergone programmed cell death.

Question 30

Many ________ bacteria cause horrific human diseases, such as tetanus, botulism, and gangrene.

A) aerobic
B) anaerobic
C) psychrophilic
D) halophilic
E) fermentative

Question 31

The proteins and cell components of halophiles have remarkably high intracellular levels of ________, which helps to maintain their cell structure.

A) oxygen
B) potassium
C) calcium
D) sodium
E) hydrogen

Question 32

An organism that grows at the top of a tube of medium containing thioglycolate is probably a(n)

A) strict aerobe.
B) facultative anaerobe.
C) aerotolerant anaerobe.
D) microaerophile.
E) strict anaerobe.

Question 33

Which of the following are often chemolithotrophs that oxidize reduced metals and generate strong acids, such as sulfuric acid?

A) acidophiles
B) psychrophiles
C) halophiles
D) mesophiles
E) barophiles

Question 34

Alkaliphiles use ________ force in addition to proton motive force to maintain pH.

A) potassium motive
B) sodium motive
C) calcium motive
D) magnesium motive
E) sulfur motive

Question 35

Which category best describes E. coli?

A) strict aerobe
B) aerotolerant anaerobe
C) facultative anaerobe
D) microaerophile
E) strict anaerobe

Question 36

Which of the following are commonly used to control microbial growth in foods?

A) weak acids
B) strong acids
C) weak bases
D) strong bases
E) enzymes

Question 37

A ________ medium is one of higher osmolarity than the cell.

A) hypertonic
B) hypotonic
C) isotonic
D) defined
E) complex

Question 38

Special channels for helping water move across the membrane quickly are called

A) compatible solutes.
B) osmolarity.
C) aquaporins.
D) mechanosensitive channels.
E) chaperones.

Question 39

E. coli tolerates a pH range from 2 to 9, which is a ________-fold difference in hydrogen ion concentration.

A) 7
B) 100
C) 1,000
D) 10,000
E) 10,000,000

Question 40

What piece of equipment is represented by the following schematic diagram?

A) a membrane filtration device
B) a pressure cooker
C) an autoclave
D) a biological safety cabinet
E) a food irradiation device

Question 41

Filtration of samples to remove microbial cells typically use micropore filters with pore sizes of

A) 1.5 mm.
B) 0.2 mm.
C) 0.1 nm.
D) 150 mm.
E) 0.2 mm.

Question 42

Runoff from agricultural fields, lawns, and golf courses can cause an overgrowth of microbes due to

A) eutrophication.
B) starvation response.
C) oligotrophy.
D) antisepsis.
E) pasteurization.

Question 43

What alkaliphile do pink flamingos eat, and how is it involved in making the flamingo pink?

Question 44

How are some organisms able to survive temporary exposures to elevated temperatures?

Question 45

A virus that infects bacteria is called a

A) bacteriophage.
B) viroid.
C) spore.
D) probiotic.
E) porin.

Question 46

A useful biocontrol alternative to antibiotics for treatment of biofilms that can potentially lead to chronic infections is

A) phenolics.
B) high temperatures and pressures.
C) commercial disinfectants.
D) x-rays.
E) bacteriophages.

Question 47

Halophiles require high salt concentrations to survive. Describe a mechanism involving compatible solutes that has evolved to achieve low internal sodium ion concentrations.

Question 48

Deinococcus radiodurans resists extreme drought and radiation by what mechanism?

A) biofilm formation
B) producing aquaporins
C) producing multidrug efflux pumps
D) endospore formation
E) repairing DNA damage

Question 49

Disposable plasticware such as petri dishes can be sterilized using which of the following?

A) ethylene oxide gas
B) steam autoclave
C) low-temperature, long-time pasteurization
D) phenol
E) 70% ethanol

Question 50

Describe one method that enables researchers to study extremophilic organisms that we cannot culture in the laboratory.

Question 51

Which of the following is NOT true concerning irradiation of foods?

A) Food consumed by NASA astronauts is sterilized by irradiation.
B) Foods become radioactive when irradiated.
C) Viruses are resistant to doses approved for foods.
D) A higher dose of radiation is necessary to kill microbes in frozen foods.
E) It is effective in eliminating parasites and bacteria.

Question 52

Why are thermophiles able to survive at temperatures that would quickly kill most mesophiles? Describe at least three adaptations.

Question 53

How does pH affect proteins? Why do proteins have an optimum, minimum, and maximum pH at which they will function?

Question 54

Give an example of a naturally occurring organic acid stress situation in the food industry. How does the food industry mimic this, and why?

Question 55

During the starvation response, only a limited number of organisms can

A) retool transport systems for the uptake of different nutrients.
B) form metabolically inactive endospores.
C) protect against reactive oxygen species.
D) protect against temperature extremes.
E) protect against pH extremes.

Question 56

The D-value of a bacterial culture heated to 100°C is the time it takes to kill ________% of the population.

A) 99
B) 90
C) 50
D) 10
E) 1

Question 57

Describe three mechanisms organisms use to reduce osmotic stress.

Question 58

Why are many barophiles also psychrophiles, and how are the adaptations for barophiles and psychrophiles similar?

Question 59

No one ever expected to find microbes thriving in our stomachs. What organism was found there, what problem does it cause, and how does it survive there?

Question 60

The conditions used in an autoclave may be reproduced at home in

A) a rice cooker.
B) a double-boiler.
C) a microwave.
D) a pressure cooker.
E) boiling water.

Question 61

What is biocontrol? Describe two examples.

Question 62

Describe the studies with Salmonella that showed that in vitro conditions do not always model what happens in vivo (in this case in the phagocytic vacuole).

Question 63

If you have a food sample contaminated with anthrax spores, which sterilization approach would make sure the sample is free of spores without compromising the quality of the food sample-autoclaving or irradiation? Why?

Question 64

Why is moist heat more efficient at killing microbes than dry heat? How does an autoclave kill microbes so efficiently?

Question 65

If a disinfectant is added to a culture containing 1 ´ 10⁶ CFU per milliliter and the D-value of the disinfectant is 2 minutes, how many viable cells are left after 4 minutes of exposure?

Question 66

Why is oxygen so dangerous for cells and how do cells deal with these problems?

Question 67

Why do some microorganisms produce antibiotics, and how do they avoid being harmed by the antibiotics they produce?

Question 68

Briefly describe three techniques used to culture anaerobes in the laboratory.

Question 69

How is the phenol coefficient calculated? Why is phenol the standard for testing other disinfectants?

Question 70

Why is death a logarithmic function and not an instantaneous event upon treatment?