BIOL124 Discussion Questions

Molecular Koch’s postulates were developed primarily to address which limitation of the original Koch’s postulates?

A. The inability to culture obligate intracellular pathogens

B. The presence of asymptomatic carriers

C. The difficulty of assigning disease causation to specific virulence factors

D. The ethical concerns of infecting healthy hosts

C

Which of the following scenarios most clearly violates the original Koch’s postulates but is still widely accepted as evidence of causation?

A. A bacterium that can only be cultured at low temperatures

B. A virus identified solely by electron microscopy

C. A pathogen detected by PCR in both diseased and healthy individuals

D. A pathogen whose disease association is supported by epidemiological and genetic evidence but lacks an animal model

D

Which experimental finding would provide the strongest functional support for disease causation under molecular Koch’s postulates?

A. The pathogen genome is consistently detected in diseased tissue

B. Deletion of a specific gene abolishes virulence, and restoration of that gene restores virulence

C. Antibodies against the pathogen are found in infected individuals

D. The pathogen induces inflammation in cell culture

B

Which statement best explains why mucosal surfaces require additional defense mechanisms beyond a physical barrier?

A. Mucosal surfaces lack immune cells

B. Mucosal epithelia are thinner and frequently exposed to the external

environment

C. Mucosal tissues are unable to regenerate after damage

D. Microorganisms cannot survive on mucosal surfaces

B

Which scenario best demonstrates a breakdown of physical barrier defenses leading to increased infection risk?

A. Increased antibody production following vaccination

B. Disruption of the gut microbiota after broad-spectrum antibiotic use

C. Activation of macrophages at a site of inflammation

D. Expansion of memory T cell populations

B

Antimicrobial proteins such as defensins and lysozyme primarily contribute to host defense by:

A. Activating adaptive immune responses

B. Enhancing antibody specificity

C. Directly damaging microbial cell structures

D. Preventing antigen presentation by host cells

C

Which statement best distinguishes symbionts from pathobionts within the normal human microbiota?

A. Symbionts are always beneficial to the host, whereas pathobionts are always pathogenic.

B. Pathobionts are transient microbes acquired from the environment, whereas symbionts are permanently colonizing organisms.

C. Symbionts participate in long-term interactions with the host, while pathobionts are normally harmless members of the microbiota that can cause disease under specific conditions.

D. Pathobionts lack co-evolutionary history with the host, whereas symbionts do not interact with the immune system.

C

Activation of Toll-like receptors (TLRs) mainly leads to:

A. Antibody secretion

B. Cytokine and chemokine production

C. DNA synthesis

D. Red blood cell maturation

B

Which type of pathogen is mainly recognized by NOD2?

A. Viruses

B. Gram-negative bacteria

C. Gram-positive bacteria

D. Fungi

C

Which complement protein mainly helps phagocytosis by coating bacteria?

A. C1

B. C3b

C. C5a

D. C9

B

What is the main role of the membrane attack complex (MAC)?

A. Activate T cells

B. Kill bacteria by making holes in the membrane

C. Produce antibodies

D. Block inflammation

B

What is a main function of cytokines?

A. Digest pathogens directly

B. Serve as energy molecules

C. Regulate and coordinate immune cell activity

D. Form antibodies

C

Which is a common outcome of the acute phase reaction?

A. Decreased immune activity

B. Fever and systemic inflammatory response

C. Reduced protein production

D. Loss of all immune cells

B

Which cytokine mainly stimulates the liver to produce acute-phase proteins?

A. IL-1

B. IL-6

C. IL-8

D. IL-12

B

Antibody Fab region is mainly responsible for:

A. Activating complement

B. Binding antigen

C. Binding Fc receptors

D. Crossing the placenta

B

During class switching, which part of the antibody is changed?

A. The antigen-binding site

B. The light chain

C. The constant region of the heavy chain

D. The variable region of the heavy chain

C

Which antibody is the dominant antibody in blood (serum)?

A. IgA

B. IgM

C. IgE

D. IgG

D

Flagellar movement in bacteria can be driven by:

A. Chemical signals (chemotaxis)

B. Light (phototaxis)

C. Oxygen (aerotaxis)

D. Random chance with no stimulus

ABC

Which bacterial structure is recognized by Toll-like receptor 5 (TLR5)?

A. Capsule

B. Lipopolysaccharide (LPS)

C. Flagellin

D. Peptidoglycan

C

A biofilm is best described as:

A. Free-floating single bacterial cells in liquid

B. A dense community of bacteria attached to a surface

C. A virus-infected host cell

D. A group of dead bacteria

C

Why is PCR amplification an essential step in building a 16S rRNA clone library?

A. To obtain complete bacterial genomes for functional analysis

B. To enrich the 16S rRNA gene from complex environmental DNA

C. To eliminate sequencing errors introduced during cloning

D. To ensure equal representation of all bacterial species

B

Which research goal is least well addressed using 16S rRNA clone library

sequencing?

A. Identifying which bacterial taxa are present in a community

B. Comparing broad differences in community composition between samples

C. Determining the metabolic capabilities of the microbial community

D. Detecting previously unknown bacterial lineages

C

Two bacterial species are present at equal cell numbers in a sample, but one species appears much more abundant in a 16S rRNA clone library. Which factor is most likely responsible for this discrepancy?

A. Differences in cell size between the two species

B. Differences in the number of 16S rRNA gene copies per genome

C. Differences in growth rate under laboratory conditions

D. Differences in GC content of the whole genome

B

Which limitation is most specifically associated with PhyloChip technology?

A. Inability to process many samples simultaneously

B. Dependence on cloning prior to analysis

C. Cross-hybridization between closely related sequences

D. Requirement for full genome sequencing

C

Which of the following microbial groups is most likely to be missed by T-RFLP or PhyloChip analysis?

A. Highly abundant bacteria with well-characterized genomes

B. Bacteria whose 16S rRNA genes match known probe sequences

C. Low-abundance or previously uncharacterized bacteria

D. Bacteria with multiple 16S rRNA gene copies

C

Why should band intensity (DGGE/TGGE) or peak height (T-RFLP) not be interpreted as a direct measure of microbial abundance?

A. DNA extraction efficiency is identical for all species

B. PCR amplification and detection introduce bias

C. These methods sequence the entire genome

B

What does “high-throughput sequencing” mean?

A. Sequencing one DNA molecule with very high accuracy

B. Sequencing many DNA molecules at the same time

C. Sequencing very long DNA fragments

D. Sequencing DNA without amplification

B

Which sequencing method is lowest throughput?

A. Illumina sequencing

B. Ion Torrent sequencing

C. PacBio sequencing

D. Sanger sequencing

D

Why does generating more sequences help detect low-abundance microbes?

A. It increases read length

B. It reduces sequencing error

C. It increases the chance of sampling rare sequences

D. It improves genome assembly

C

Which sequencing feature is most useful for sequencing many 16S samples at

once?

A. Long read length

B. High accuracy per base

C. Massively parallel sequencing

D. Manual sample processing

C

A metagenomic study finds that Bacterium X is significantly more abundant in patients with inflammatory bowel disease than in healthy controls. Which conclusion is most scientifically appropriate?

A. Bacterium X is the direct cause of inflammatory bowel disease

B. Bacterium X contributes to disease severity in all patients

C. Bacterium X is associated with inflammatory bowel disease

D. Bacterium X must be targeted to cure the disease

C

Why does the increased abundance of a microbe in diseased individuals not automatically satisfy Koch’s postulates?

A. Koch’s postulates require that the microbe be present only during disease

B. Koch’s postulates require experimental evidence that the microbe causes disease

C. Koch’s postulates apply only to viruses, not bacteria

D. Koch’s postulates require sequencing of the entire microbial genome

B