Question 1

You inoculate a bacterium into three tubes of nutrient broth medium containing added salt: 0.5% NaCl, 5% NaCl, and 15% NaCl. After incubation, you notice signi?cant turbidity in the 15% NaCl medium and modest turbidity in the 5% NaCl medium. There is no growth in the third tube. This organism would be termed ______.

Accepted Answer

The organism's growth in high salt concentrations (5% and 15% NaCl) but not in lower salt concentration (0.5% NaCl) indicates it is halophilic, meaning it thrives in high salt environments.

Question 2

In a close relationship, a change in one partner that results from a change in the other partner is termed ______.

Accepted Answer

Coevolution refers to the process where changes in one species lead to changes in another species, often seen in close relationships like those between partners.

Question 3

In a commensal relationship, the commensal bene?ts but the cohabitant is neither harmed nor bene?ted.

Accepted Answer

In a commensal relationship, only one organism benefits, while the other is not affected positively or negatively.

Question 4

Organisms called _______ live on or in the body of a host and cause some degree of harm.

Accepted Answer

Pathogens are organisms that live on or in a host organism and cause disease or harm to the host. This includes a wide range of organisms, such as viruses, bacteria, fungi, and parasites.

Question 5

Which of the following properties is likely to be found in a pioneer colonizer of a bioﬁlm on an artiﬁcial joint implant?

Accepted Answer

Surface structures for attaching to tissue are likely to be found in a pioneer colonizer of a biofilm on an artificial joint implant because they would allow the bacterium to adhere to the implant and form a biofilm.

Question 6

What is the difference between mutualism and synergism?

Accepted Answer

In a mutualistic relationship, both organisms benefit from the interaction and often, though not always, depend on each other to a certain extent. This dependency can vary in degree, but mutualism is characterized by the mutual benefit derived from the relationship. Synergism, on the other hand, refers to the interaction of two or more agents, factors, or substances to produce a combined effect greater than the sum of their separate effects, and does not inherently imply a biological relationship or dependency as mutualism does.

Question 7

A halophile would grow best in ______.

Accepted Answer

Halophiles are organisms that thrive in high salt concentrations, such as those found in salt lakes.

Question 8

The bio?lm that forms in your shower ("shower curtain scum") can tolerate exposure to hot water when you shower and is resistant to desiccation between showers. The microbes in the bio?lm are not endospores, so what is the best explanation for their survival under these conditions?

Accepted Answer

Biofilms provide a protective environment for the microbes within them, allowing some to survive harsh conditions by being embedded deeply away from direct exposure. This protection is not necessarily due to the presence of endospores or thermophiles but is a characteristic of the biofilm structure itself.

Question 9

When microbes are in a close nutritional relationship and one beneﬁts but the other is not harmed, it is called ______.

Accepted Answer

Commensalism describes a relationship where one organism benefits and the other is neither harmed nor helped.

Question 10

The majority of microbes live and grow in habitats between pH 7 and 9.

Accepted Answer

Most microbes prefer a neutral pH environment (around pH 7) for growth and survival, although some can tolerate or thrive in more acidic or basic conditions.

Question 11

You have inoculated a Clostridium species into a tube of media. After incubation, you observe that there is no growth, and you remember that Clostridium is an obligate anaerobe. What is the best explanation for the observed lack of growth?

Accepted Answer

Clostridium species are obligate anaerobes, meaning they cannot tolerate oxygen. The lack of growth is likely because they do not possess the necessary enzymes to neutralize toxic oxygen species, leading to their inability to survive in oxygenated environments.

Question 12

Termites are insects that require the protozoan Trichonympha in their gut to synthesize the enzyme cellulase to degrade the cellulose in wood. The protozoan uses the end products of the cellulose breakdown (glucose). This is a/an ______ relationship.

Accepted Answer

This is a mutualistic relationship because both the termites and the protozoan Trichonympha benefit from each other. The termites get help in breaking down cellulose into glucose, which they can use for energy, while the protozoans get a habitat and access to food (the glucose produced from cellulose breakdown).

Question 13

Microorganisms that live in severe habitats, such as very hot, acidic, or salty environments, are called ______.

Accepted Answer

Extremophiles are microorganisms that thrive in physically or geochemically extreme conditions that are detrimental to most life on Earth.

Question 14

When microbes live independently but cooperate and share nutrients, it is called ______.

Accepted Answer

Synergism refers to the interaction between two or more organisms to produce a combined effect greater than the sum of their separate effects, often involving the sharing of nutrients while living independently.

Question 15

A barophile would grow best in ______.

Accepted Answer

Barophiles are organisms that thrive under high pressure conditions, such as those found in deep oceans.

Question 16

A bacterium is inoculated into a tube of thioglycollate and incubated. After incubation, turbidity appears throughout, top to bottom, with the greatest turbidty at the very top. This bacterium would be called a(n) ______.

Accepted Answer

Facultative anaerobes can grow throughout the medium but show more growth at the top where oxygen is present, indicating they can use oxygen but can also grow without it.

Question 17

Most microorganisms can only grow in habitats that are similar to human body conditions.

Accepted Answer

Most microorganisms can grow in a wide range of habitats, including extreme environments that are very different from human body conditions.

Question 18

After using jelly on a sandwich, you close the jar and place it on a room temperature shelf instead of in the refrigerator. When you open the jar several weeks later, you notice microbial growth on the surface. What type of organism is likely to grow in this environment?

Accepted Answer

Fungus is likely to grow in this environment because fungi can thrive in environments with high sugar content, like jelly, especially when it is not refrigerated. They are more capable of growing in such conditions compared to viruses, bacteria, and protozoa, which might require more specific conditions to grow, such as moisture or a living host in the case of viruses.

Question 19

Anaerobes can be cultured in a CO₂ environment.

Accepted Answer

Anaerobes can grow in an environment that contains little to no oxygen, such as a CO₂ environment. This is commonly done in laboratory settings to culture anaerobic bacteria.

Question 20

The production of antibiotics is a form of antagonism called ______.

Accepted Answer

Antibiosis is the correct term for the production of antibiotics, which is a form of antagonism where one organism produces substances to inhibit or kill another organism.

Quiz 7: Microbial Nutrition and Growth