Q: A scientist is studying a bacterial culture that doubles every 30 minutes. If she starts with 1,000 cells, how many cells will there be after 2 hours? Use the formula $$N = N_0$ \times 2^n$$, where $$N is $$the final number of cells, $$N_0 is $$the initial number, and $$n is $$the number of generations.

$$N = 1,000 \times 2^4$ = 16,000$$ cells

Question 1

Which of the following best explains how Louis Pasteur disproved the theory of spontaneous generation?

Accepted Answer

He used a swan-neck flask to show that microorganisms did not grow in sterilized broth unless exposed to air, supporting biogenesis.

Question 2

A patient is diagnosed with tuberculosis. Which staining technique would be most appropriate to confirm the presence of Mycobacterium tuberculosis in a sputum sample, and why?

Accepted Answer

Acid-fast stain, because Mycobacterium species have waxy mycolic acids in their cell walls that retain the primary stain.

Question 3

Which of the following best describes the difference between an opportunistic pathogen and a true pathogen?

Accepted Answer

An opportunistic pathogen causes disease only when the host's defenses are compromised, while a true pathogen can cause disease in healthy individuals.

Question 4

A scientist is studying a bacterial culture that doubles every 30 minutes. If she starts with 1,000 cells, how many cells will there be after 2 hours? Use the formula $$N = N_0$ 	imes 2^n$$, where $$N is $$the final number of cells, $$N_0 is $$the initial number, and $$n is $$the number of generations.

Accepted Answer

$$N = 1,000 	imes 2^4$ = 16,000$$ cells

Question 5

Which of the following statements about Gram-positive and Gram-negative bacterial cell walls is correct?

Accepted Answer

Gram-positive bacteria have a thick peptidoglycan layer and teichoic acids, while Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane containing lipopolysaccharide.

Question 6

A patient is prescribed a beta-lactam antibiotic. Which of the following best describes the mechanism of action of this drug class?

Accepted Answer

They inhibit the synthesis of peptidoglycan, weakening the bacterial cell wall and leading to cell lysis.

Question 7

Which of the following best explains why RNA viruses tend to evolve more rapidly than DNA viruses?

Accepted Answer

RNA-dependent RNA polymerases lack proofreading activity, leading to higher mutation rates.

Question 8

A patient with a history of repeated antibiotic use develops a Clostridium difficile infection. Which of the following best explains why this occurs?

Accepted Answer

Antibiotic use disrupts normal gut microbiota, allowing C. difficile to proliferate and cause disease.

Question 9

Which of the following best describes the function of NAD+ in cellular metabolism?

Accepted Answer

It acts as an electron carrier, accepting electrons during redox reactions and becoming reduced to NADH.

Question 10

A patient is exposed to a pathogen with a high ID50 and a low LD50. What does this indicate about the pathogen?

Accepted Answer

A high ID50 means a large number of organisms are needed to cause infection, while a low LD50 means it is highly lethal.

Question 11

Which of the following best describes the difference between sterilization and disinfection?

Accepted Answer

Sterilization destroys all forms of microbial life, including endospores, while disinfection reduces or eliminates most pathogens but may not remove endospores.

Question 12

A researcher is using Koch’s postulates to determine the causative agent of a new disease. Which step would be impossible to fulfill if the suspected pathogen only infects humans and cannot be ethically tested in animals?

Accepted Answer

The step requiring the pathogen to be introduced into a healthy host to reproduce the disease.

Question 13

Which of the following best describes the role of buffers in biological systems?

Accepted Answer

Buffers stabilize pH by accepting or donating protons ($$H^+) to $$minimize changes in hydrogen ion concentration.

Question 14

A patient is diagnosed with a type I hypersensitivity reaction. Which of the following best describes the immunological mechanism involved?

Accepted Answer

IgE antibodies bind to mast cells and basophils, leading to degranulation and release of histamine upon allergen exposure.

Question 15

Which of the following best explains why endospores are a challenge in healthcare sanitation practices?

Accepted Answer

Endospores are highly resistant to heat, desiccation, chemicals, and radiation, making them difficult to eliminate with standard disinfection methods.

Question 16

A patient receives a live attenuated vaccine. Which of the following is a key advantage of this type of vaccine?

Accepted Answer

It stimulates a strong, long-lasting immune response by mimicking a natural infection.

Question 17

Which of the following best describes the function of the complement system in innate immunity?

Accepted Answer

It enhances the ability of antibodies and phagocytic cells to clear microbes by promoting opsonization, inflammation, and cell lysis.

Question 18

A patient is exposed to a chemical mutagen that causes thymine dimers in DNA. If these dimers are not repaired, what is the most likely consequence?

Accepted Answer

DNA replication will be blocked or result in mutations, potentially leading to cell death or cancer.

Question 19

Which of the following best describes the difference between an epidemic and a pandemic?

Accepted Answer

An epidemic is a sudden increase in cases in a specific region, while a pandemic is a global outbreak affecting multiple countries or continents.

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