Question 1

The average adult carries 10 times more microbial cells (10¹⁴)than human cells (average about 10¹³).

Accepted Answer

This is a well-established fact in the field of microbiology. The vast majority of these microbial cells are harmless or even beneficial to our health.

Question 2

Microorganisms in the human colon are more often being described as mutualistic with human hosts rather than commensalistic.Why has this change in the definition of a symbiotic relationship occurred?

Accepted Answer

The change in definition from commensalistic to mutualistic has occurred as we learn more about the important roles that microorganisms play in the human immune system, vitamin production, and other essential processes. It has become clear that humans depend on these microorganisms for various benefits, and thus the relationship between microorganisms and humans can be seen as mutualistic rather than simply commensalistic.

Question 3

Although the intestinal microbiota for most people consists of the same types of organisms,the relative percentages of organisms varies significantly from person to person.

Accepted Answer

The answer of Although the intestinal microbiota for most people...

Question 4

Which of the following types of experimental evidence suggests that a particular organism thought to be part of the human microbiome is,in fact,just a laboratory contaminant?

Accepted Answer

CThe absence of ribosomal RNA evidence in a specific host location where the organism was believed to have colonized (A) suggests that the organism may not actually be a part of the microbiome but rather a contaminant, as its genetic material cannot be found where it was expected. Similarly, the absence of ribosomal RNA evidence in a location where the organism was not expected to have colonized (C) can also indicate contamination, as it suggests the organism's presence is not consistent with known colonization patterns, potentially due to laboratory contamination rather than actual colonization.

Question 5

Biofilm formation by Pseudomonas bacteria on the surface of a natural loofa sponge kept in the shower is an example of which type of relationship?

Accepted Answer

Commensalism is a type of relationship where one organism benefits and the other organism is neither helped nor harmed. In this case, Pseudomonas bacteria form biofilms on the surface of a natural loofa sponge in a shower, which does not harm the sponge, but the bacteria benefit from the nutrients and protection the sponge provides.

Question 6

The oral cavity of humans normally becomes colonized with microorganisms within hours after birth.

Accepted Answer

This is true. Babies are exposed to microorganisms during birth and through contact with their mothers and the environment, leading to rapid colonization of the oral cavity with microorganisms.

Question 7

When members of the normal microbiota of the human body become pathogenic and produce disease under certain circumstances,they are referred to as ______________ pathogens.

Accepted Answer

Opportunistic pathogens are members of the normal microbiota that can cause disease under certain conditions, such as when the immune system is weakened or when the normal microbiota is disrupted. The other choices (partial, conditional, occasional) do not accurately describe this phenomenon.

Question 8

The relationship between Trichonympha protozoa and its termite host,and Xenorhabdus bacteria and its nematode host,are both obligatory relationships.

Accepted Answer

The answer of The relationship between Trichonympha protozoa and its...

Question 9

A germfree mouse that is not born by cesarean section is not a suitable animal model for investigating the interaction between a host and one type of bacteria.

Accepted Answer

A germfree mouse must be delivered by cesarean section to ensure it is not exposed to any microorganisms, maintaining its germfree status for controlled studies on host-bacteria interactions.

Question 10

Why were the advent of metagenomics,and the application of molecular techniques such as single-cell and next-generation sequencing,important for defining a microbial relationship?

Accepted Answer

The advent of metagenomics and molecular techniques such as single-cell and next-generation sequencing allowed for a deeper understanding of microbial communities and their relationships with hosts. These methods revealed that symbiotic relationships can exist between a host and one to thousands or more microorganisms, challenging the former definition of a symbiotic relationship as one that occurs between a single microbe and its host. This new understanding has implications for fields such as medicine and agriculture, where microbial relationships play an important role.

Question 11

Insects frequently contain bacteria in their cytoplasm,and these bacteria form a mutualistic association with their host.

Accepted Answer

Many insects have symbiotic bacteria that they require for their survival, such as those that aid in digestion or provide essential nutrients. These bacteria live within the insect's cytoplasm and benefit from the stable environment and nutrients provided by the host. This relationship is known as mutualism.

Question 12

Recent research has demonstrated a correlation between the presence of certain types of Gram-positive bacteria in the human gut with obesity and type 2 diabetes.These findings best support which of the following statements?

Accepted Answer

The findings suggest that the normal microbiota in the human gut may greatly impact human health and disease. The presence of certain Gram-positive bacteria in the gut is correlated with obesity and type 2 diabetes, indicating the importance of the microbiota in these conditions. However, this does not prove causation, as other factors may also be involved. Therefore, A is the best answer. B, C, and D are not supported by the evidence presented.

Question 13

How are termite-related protists and aphid-related proteobacteria similar?

Accepted Answer

Both termite-related protists and aphid-related proteobacteria are mutualists with their respective hosts. The termite-related protists help break down wood in the termite's digestive system, while the aphid-related proteobacteria provide essential amino acids to the aphid.

Question 14

Pseudonocardia is an organism that is hosted by

Accepted Answer

Pseudonocardia is commonly found in ants that cultivate fungal gardens. These ants rely on Pseudonocardia to produce antibiotics that protect their fungal crops from harmful bacteria and fungi.

Question 15

A researcher proposes that the relationship between a particular bacterial species that produces a fat-soluble vitamin is mutualistic with its insect host.Which of the following procedures would best test the researcher's hypothesis?

Accepted Answer

This procedure directly tests the relationship between the bacterial species and the insect host by determining if the insect can grow without the vitamin produced by the bacteria. The use of an antibiotic that selectively targets only the bacteria ensures that any changes in growth are due to the removal of the bacteria and not the antibiotic itself. The other procedures do not directly test the mutualistic relationship between the bacterial species and the insect host.

Question 16

Several cases of an emerging infectious disease are reported in workers at a research station that borders a tropical rainforest region.The pathogen is identified as a species of bacteria carried by nematodes that infect mosquitos,and disease transmission occurs in a human host following a mosquito bite.Which organisms should be targeted in the treatment of infected patients?

Accepted Answer

The primary target for treatment in infected patients should be the nematode and the bacteria, as these are the direct causes of the disease in humans. The mosquito serves as a vector for transmission, but targeting the mosquito does not treat an existing infection.

Question 17

Microorganisms commonly associated with the human body are traditionally referred to as the

Accepted Answer

Both choices A and C are correct and interchangeable in referring to microorganisms commonly found on and in the human body. Choice B is not as commonly used and does not specify the relationship to the human body. Therefore, choice D is the best option as it includes both A and C, which are the most commonly used terms.

Question 18

A microbiologist studying the human microbiome is interested in how a particular bacterial species may impact water absorption in the large intestine.Which of the following models is appropriate for this investigation?

Accepted Answer

The answer of A microbiologist studying the human microbiome is...

Question 19

Which of the following processes is not one that is common to all symbionts?

Accepted Answer

Predation is not a process common to all symbionts as predation involves one organism consuming another, while symbiosis is a long-term, close association between two or more different species.

Question 20

A _________ is any disease-producing microorganism.

Accepted Answer

The answer of A _________ is any disease-producing microorganism....

Quiz 32: Microbial Interactions

The average adult carries 10 times more microbial cells (1014)than human cells (average about 1013).