1 Inquire through: | Professional | Confidential Support
Chapter 6: Microbial Growth Questions and
Answers (100% Correct Answers)
Why are hyperthermophiles that grow at temperatures above 100°C seemingly
limited to oceanic depths? 6-1
Ans: The immense pressure in the ocean depths prevents water from boiling even at
temperatures well above 100°C.
Other than controlling acidity, what is an advantage of using phosphate salts as
buffers in growth media? 6-2
Ans: 1. They are nontoxic,
2. they provide phosphorus, an essential nutrient
why might primitive civilizations have used food preservation techniques that rely
on osmotic pressure? 6-3
Ans: Growth of the cell is inhibited as the plasma membrane pulls away from the
cell wall. The high salt or sugar concentrations draw water out of any microbial cells,
thus prevent their growth.
If bacterial cells were given a sulfur source containing radioactive sulfur (35S) in
their culture media, in what molecules would the 35S be found in the cells? 6-4
Ans: amino acids, proteins, RNA and DNA
How would one determine whether a microbe is a strict anaerobe? 6-5
Ans: Bacteria only grows @ bottom of tube where where 0 oxygen has touched or
diffused
Oxygen is so pervasive in the environment that it would be very difficult for a
microbe to always avoid physical contact with it. What, therefore, is the most
obvious way for a microbe to avoid damage? 6-6
Ans: cannot avoid contact w/ O2, must have mechanisms to turn O2 into something
less harmful:
SOD (superoxide dusmutase), catalase, peroxidase, hydroxyl radical
Identify a way in which pathogens find it advantageous to form biofilms. 6-7
Ans: Cell-to-cell communication, aka quorum sensing.
Single species of a diverse group of microorganisms.
Share nutrients & shelter
Could humans exist on chemically defined media, at least under laboratory
conditions? 6-8
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Ans: Yes. Has energy source + carbon, nitrogen, sulfur, phosphorus, and organic
growth factors (organism unable to synthesize itself)
Could Louis Pasteur, in the 1800s, have grown rabies viruses in cell culture instead
of in living animals? 6-9
Ans: No. Viruses need a living host to reproduce in
What BSL is your laboratory? 6-10
Ans: BSL1-basic microbio teaching lab
(BSL2-moderate infection risk
BSL3- highly infectious airborne pathogens
BSL4- "hot zone"- dangerous microbes)
Can you think of any reason why a colony does not grow to an infinite size, or at
least fill the confines of the Petri plate? 6-11
Ans: Limited nutrients in petri dish
Could a pure culture of bacteria be obtained by the streak plate method if there were
only one desired microbe in a bacterial suspension of billions? 6-12
Ans: Possible. Need selective media first to kill unwanted microbes THEN streak
plate to isolate
If the Space Station in Earth orbit suddenly ruptured, the humans on board would die
instantly from cold and the vacuum of space. Would all the bacteria in the capsule
also be killed? 6-13
Ans: No. Can survive and be revived by hydration (liquid nutrient medium)
Can a complex organism, such as a beetle, divide by binary fission? 6-14
Ans: No. MITOSIS (more complex)
If two mice started a family within a fixed enclosure, with a fixed food supply, would
the population curve be the same as a bacterial growth curve? 6-15
Ans: Yes.
Lag phase: mice slowly reproduce
Log phase: exponential population increase
Stationary phase: born at same rate dying
Death phase: more dying than reproducing
Chapter 6: Microbial Growth Questions and
Answers (100% Correct Answers)
Why are hyperthermophiles that grow at temperatures above 100°C seemingly
limited to oceanic depths? 6-1
Ans: The immense pressure in the ocean depths prevents water from boiling even at
temperatures well above 100°C.
Other than controlling acidity, what is an advantage of using phosphate salts as
buffers in growth media? 6-2
Ans: 1. They are nontoxic,
2. they provide phosphorus, an essential nutrient
why might primitive civilizations have used food preservation techniques that rely
on osmotic pressure? 6-3
Ans: Growth of the cell is inhibited as the plasma membrane pulls away from the
cell wall. The high salt or sugar concentrations draw water out of any microbial cells,
thus prevent their growth.
If bacterial cells were given a sulfur source containing radioactive sulfur (35S) in
their culture media, in what molecules would the 35S be found in the cells? 6-4
Ans: amino acids, proteins, RNA and DNA
How would one determine whether a microbe is a strict anaerobe? 6-5
Ans: Bacteria only grows @ bottom of tube where where 0 oxygen has touched or
diffused
Oxygen is so pervasive in the environment that it would be very difficult for a
microbe to always avoid physical contact with it. What, therefore, is the most
obvious way for a microbe to avoid damage? 6-6
Ans: cannot avoid contact w/ O2, must have mechanisms to turn O2 into something
less harmful:
SOD (superoxide dusmutase), catalase, peroxidase, hydroxyl radical
Identify a way in which pathogens find it advantageous to form biofilms. 6-7
Ans: Cell-to-cell communication, aka quorum sensing.
Single species of a diverse group of microorganisms.
Share nutrients & shelter
Could humans exist on chemically defined media, at least under laboratory
conditions? 6-8
, 2 Inquire through: | Professional | Confidential Support
Ans: Yes. Has energy source + carbon, nitrogen, sulfur, phosphorus, and organic
growth factors (organism unable to synthesize itself)
Could Louis Pasteur, in the 1800s, have grown rabies viruses in cell culture instead
of in living animals? 6-9
Ans: No. Viruses need a living host to reproduce in
What BSL is your laboratory? 6-10
Ans: BSL1-basic microbio teaching lab
(BSL2-moderate infection risk
BSL3- highly infectious airborne pathogens
BSL4- "hot zone"- dangerous microbes)
Can you think of any reason why a colony does not grow to an infinite size, or at
least fill the confines of the Petri plate? 6-11
Ans: Limited nutrients in petri dish
Could a pure culture of bacteria be obtained by the streak plate method if there were
only one desired microbe in a bacterial suspension of billions? 6-12
Ans: Possible. Need selective media first to kill unwanted microbes THEN streak
plate to isolate
If the Space Station in Earth orbit suddenly ruptured, the humans on board would die
instantly from cold and the vacuum of space. Would all the bacteria in the capsule
also be killed? 6-13
Ans: No. Can survive and be revived by hydration (liquid nutrient medium)
Can a complex organism, such as a beetle, divide by binary fission? 6-14
Ans: No. MITOSIS (more complex)
If two mice started a family within a fixed enclosure, with a fixed food supply, would
the population curve be the same as a bacterial growth curve? 6-15
Ans: Yes.
Lag phase: mice slowly reproduce
Log phase: exponential population increase
Stationary phase: born at same rate dying
Death phase: more dying than reproducing
