Question 1

Nitrogen is a growth-limiting nutrient for many organisms because
A) it is necessary for the biosynthesis of amino acids.
B) it is required for synthesis of nucleotides.
C) it is required for lipid synthesis.
D) only a small number of bacteria are able to extract it from the atmosphere.
E) only a few microbes can extract it from the atmosphere, but all organisms require it for amino acid and nucleotide synthesis.

Accepted Answer

Nitrogen is a crucial element for all living organisms as it is a fundamental component of amino acids (which make up proteins) and nucleotides (which make up DNA and RNA). However, despite its abundance in the atmosphere, most organisms cannot directly utilize atmospheric nitrogen. Only certain bacteria and archaea have the capability to fix atmospheric nitrogen into a form that can be used by other organisms. This process is known as nitrogen fixation. Therefore, nitrogen becomes a growth-limiting nutrient because its bioavailable form is relatively scarce, and its fixation is limited to certain microorganisms, making it a bottleneck for the biosynthesis of essential biomolecules like amino acids and nucleotides.

Question 2

Which of the following organisms would be most likely to contaminate a jar of pickles?
A) a neutrophile
B) a thermophile
C) an acidophile
D) an obligate anaerobe
E) a mesophile

Accepted Answer

Acidophiles thrive in acidic environments, making them the most likely to contaminate a jar of pickles due to the acidic nature of the pickling solution.

Question 3

A fastidious organism might be grown on which of the following types of media?
A) transport media
B) reducing media
C) enriched media
D) differential media
E) selective media

Accepted Answer

Enriched media contains a variety of nutrients that support the growth of fastidious organisms, which have specific nutritional requirements. This type of media is commonly used to culture organisms that require additional nutrients, growth factors, or vitamins to proliferate. Selective media may inhibit the growth of certain bacteria, and differential media may highlight metabolic differences between different species, but neither of these types of media is necessarily designed to support the growth of fastidious organisms.

Question 4

A microorganism grows in the lab on medium containing mineral salts but no organic compounds. The organism is likely to be a(n)
A) heterotroph.
B) autotroph.
C) chemotroph.
D) chemoheterotroph.
E) The answer cannot be determined from the information provided.

Accepted Answer

The medium containing mineral salts but no organic compounds is essentially a minimal medium, which means that the microorganism must be able to synthesize all its necessary organic compounds using inorganic sources. This rules out the possibility of the microorganism being a heterotroph, which requires preformed organic compounds, or a chemoheterotroph, which derives energy from organic compounds. Therefore, the microorganism is likely to be an autotroph, which can synthesize its own organic compounds from inorganic sources. It could also be a phototroph if it uses light as an energy source, but this information is not given in the question.

Question 5

An epidemiologist is investigating a new disease and observes what appear to be bacteria inside tissue cells in clinical samples from victims. The scientist wants to try to isolate the bacteria in the lab. What culture conditions are most likely to be successful?
A) culturing on blood agar plates
B) inoculation of EMB plates
C) incubation in an anaerobic culture system
D) inoculation of cell cultures
E) inoculation of a minimal medium broth

Accepted Answer

Since the bacteria are found inside tissue cells, it is likely that they are obligate intracellular bacteria that require host cells to grow. Therefore, inoculation of cell cultures would be the most appropriate culture condition to successfully isolate the bacteria in the lab.

Question 6

The absence of ________ leaves obligate anaerobes susceptible to killing by oxygen.
A) carotenoids
B) superoxide dismutase
C) peroxidase
D) vitamin E
E) catalase

Accepted Answer

The answer of The absence of ________ leaves obligate anaerobes...

Question 7

In the process of ________, microbes detect the presence and density of other microbes and modify their metabolic activity in response.
A) quorum sensing
B) antagonism
C) mutualism
D) symbiosis
E) synergy

Accepted Answer

Quorum sensing is a process by which microbes detect the presence and density of other microbes in their environment through the secretion and detection of signaling molecules. This allows them to coordinate their behavior and modify their metabolic activity in response to the population density of other microbes.

Question 8

Ted heats some food just to boiling, and stores some of it immediately in a container which he places in the refrigerator. A week later he takes the food out and finds it has spoiled. The microbes responsible are probably
A) thermoduric.
B) thermophiles.
C) mesophiles.
D) hyperthermophiles.
E) psychrophiles.

Accepted Answer

Thermoduric microbes can survive heating to boiling, but they cannot grow at refrigeration temperatures.

Question 9

The carotenoid pigments of some phototrophs interact with ________ to reduce its toxicity.
A) singlet oxygen (¹O₂)
B) hydroxyl radical (HO⁻)
C) peroxide anion (O₂²⁻)
D) superoxide radical (O₂⁻)
E) molecular oxygen (O₂)

Accepted Answer

The carotenoid pigments of some phototrophs interact with singlet oxygen (¹O₂) to reduce its toxicity by quenching it and converting it to a ground state. This helps prevent oxidative damage to cells and tissues.

Question 10

Organisms that can grow with or without oxygen present are
A) obligate aerobes.
B) facultative anaerobes.
C) aerotolerant anaerobes.
D) obligate anaerobes.
E) either facultative anaerobes or aerotolerant anaerobes.

Accepted Answer

Facultative anaerobes can grow in the presence or absence of oxygen, adjusting their metabolism accordingly. Aerotolerant anaerobes can also grow in the presence or absence of oxygen, but unlike facultative anaerobes, they do not use oxygen for growth.

Question 11

Obligate anaerobes may be cultured in the laboratory
A) in a reducing medium.
B) in a standard incubator.
C) in standard Petri plates.
D) on blood agar plates.
E) in standard complex media.

Accepted Answer

Obligate anaerobes require an environment devoid of oxygen for growth. Therefore, they can be cultured in a reducing medium that eliminates oxygen from the culture.

Question 12

Joan wants to discover a microbe capable of degrading an environmental contaminant. Which of the following culturing methods would be most effective for isolation of such an organism?
A) cell culture
B) chemostat
C) quorum sensing
D) enrichment culture
E) differential culture

Accepted Answer

Enrichment culture is the most effective culturing method for isolating microorganisms capable of degrading specific compounds from complex environmental samples. In this method, the sample is enriched in a selective medium that favors the growth of microorganisms with the desired metabolic activity, and inhibits the growth of other organisms. This can be done by manipulating variables such as the pH, nutrient availability, and temperature to create a specific environment that favors the growth of the target organism. Once the organism is isolated, it can be further studied and characterized to determine its potential for bioremediation applications.

Question 13

A microbe that grows only at the bottom of a tube of thioglycollate medium is probably a(n)
A) obligate aerobe.
B) facultative anaerobe.
C) aerotolerant anaerobe.
D) microaerophile.
E) obligate anaerobe.

Accepted Answer

Microbes that grow only at the bottom of a tube of thioglycollate medium are likely to be obligate anaerobes. Thioglycollate medium is a type of differential medium used to test the oxygen requirements of microorganisms. It contains a reducing agent (thioglycollate) that removes oxygen and creates an anoxic environment at the bottom of the tube. Obligate anaerobes are microorganisms that require an oxygen-free environment to grow, as they cannot tolerate oxygen. Therefore, they will only grow at the bottom of the tube where there is no oxygen present.

Question 14

An organism that requires chemical nutrients which serve as final electron acceptors is a(n)
A) chemotroph.
B) phototroph.
C) lithotroph.
D) autotroph.
E) aerobe.

Accepted Answer

Chemotrophs are organisms that obtain energy by oxidizing electron donors in their environments. These electron donors can be organic or inorganic chemicals. In the process, the chemical energy is converted to ATP through cellular respiration, where chemical nutrients serve as final electron acceptors.

Question 15

The events of binary fission are
I. the cell doubles in size
II. the DNA is replicated
III. the cell forms a septum
IV. the cell separates from its offspring
The CORRECT order of these events is
A) I, III, II, IV.
B) II, III, I, IV.
C) IV, I, III, II.
D) II, I, III, IV.
E) I, II, IV, III.

Accepted Answer

The correct order of events in binary fission starts with the replication of DNA (II), followed by the cell doubling in size (I), then the formation of a septum (III), and finally, the cell separates from its offspring (IV).

Question 16

An aquatic microbe that can grow only near the surface of the water is probably which of the following?
A) a phototroph
B) a heterotroph
C) a chemotroph
D) a lithotroph
E) an anaerobe

Accepted Answer

A microbe that can grow only near the surface of the water is likely to be a phototroph, as it needs sunlight for photosynthesis. Heterotrophs can grow at various depths as they obtain their energy from organic matter. Chemotrophs obtain their energy from chemicals and do not require sunlight, but they can grow at various depths. Lithotrophs obtain their energy from inorganic compounds and can also grow at various depths. Anaerobes do not require oxygen, but their depth preference depends on their source of energy.

Question 17

At temperatures higher than the maximum growth temperature for an organism
A) proteins are permanently denatured.
B) membranes become too fluid for proper function.
C) hydrogen bonds within molecules are broken.
D) hydrogen bonds are broken and proteins are permanently denatured.
E) hydrogen bonds are broken, proteins are denatured, and membranes become too fluid.

Accepted Answer

At temperatures higher than the maximum growth temperature for an organism, several detrimental effects occur: hydrogen bonds within molecules are broken, which can lead to the denaturation of proteins, and the membranes can become too fluid, impairing their function. These changes disrupt cellular processes and can lead to cell death.

Question 18

A cell that uses an organic carbon source and obtains energy from light would be called a
A) photoheterotroph.
B) lithoautotroph.
C) photoautotroph.
D) chemoheterotroph.
E) chemoautotroph.

Accepted Answer

A cell that uses an organic carbon source and obtains energy from light is a photoheterotroph. This is because it obtains its energy from light and its carbon from organic compounds.

Question 19

A microbiologist inoculates a flask of broth to a concentration of 100 bacterial cells per ml. The generation time of the species is 1 hour, and there is no lag phase. How long will it be before the culture contains more than 6,000 cells per ml?
A) 12 hours
B) 6 hours
C) 2 hours
D) 4 hours
E) 10 hours

Accepted Answer

The answer of A microbiologist inoculates a flask of broth...

Question 20

A(n) ________ organism require(s) oxygen for growth.
A) anaerobic
B) facultative anaerobic
C) aerotolerant
D) obligate aerobic
E) aerotolerant and an anaerobic

Accepted Answer

Obligate aerobes require oxygen for growth and metabolism. They cannot survive in the absence of oxygen.

Quiz 6: Microbial Nutrition and Growth

Nitrogen is a growth-limiting nutrient for many organisms because

Which of the following organisms would be most likely to contaminate a jar of pickles?

A fastidious organism might be grown on which of the following types of media?

A microorganism grows in the lab on medium containing mineral salts but no organic compounds. The organism is likely to be a(n)

An epidemiologist is investigating a new disease and observes what appear to be bacteria inside tissue cells in clinical samples from victims. The scientist wants to try to isolate the bacteria in the lab. What culture conditions are most likely to be successful?

The absence of ________ leaves obligate anaerobes susceptible to killing by oxygen.

In the process of ________, microbes detect the presence and density of other microbes and modify their metabolic activity in response.

Ted heats some food just to boiling, and stores some of it immediately in a container which he places in the refrigerator. A week later he takes the food out and finds it has spoiled. The microbes responsible are probably

The carotenoid pigments of some phototrophs interact with ________ to reduce its toxicity.

Organisms that can grow with or without oxygen present are

Obligate anaerobes may be cultured in the laboratory

Joan wants to discover a microbe capable of degrading an environmental contaminant. Which of the following culturing methods would be most effective for isolation of such an organism?

A microbe that grows only at the bottom of a tube of thioglycollate medium is probably a(n)

An organism that requires chemical nutrients which serve as final electron acceptors is a(n)

The events of binary fission are I. the cell doubles in size II. the DNA is replicated III. the cell forms a septum IV. the cell separates from its offspring The CORRECT order of these events is

An aquatic microbe that can grow only near the surface of the water is probably which of the following?

At temperatures higher than the maximum growth temperature for an organism

A cell that uses an organic carbon source and obtains energy from light would be called a

A microbiologist inoculates a flask of broth to a concentration of 100 bacterial cells per ml. The generation time of the species is 1 hour, and there is no lag phase. How long will it be before the culture contains more than 6,000 cells per ml?

A(n) ________ organism require(s) oxygen for growth.