Question 1

Which of the following best describes the process of Gram staining and explains why it differentiates between Gram-positive and Gram-negative bacteria?

Accepted Answer

Gram staining involves a series of steps: crystal violet, iodine (mordant), alcohol decolorization, and safranin counterstain. Gram-positive bacteria retain the crystal violet-iodine complex because of their thick peptidoglycan layer, while Gram-negative bacteria lose the primary stain due to their thin peptidoglycan and outer membrane.

Question 2

A patient is diagnosed with tuberculosis. Which staining technique would be most appropriate to confirm the presence of Mycobacterium tuberculosis, and what unique cell wall component does this technique target?

Accepted Answer

Acid-fast staining; targets mycolic acid.

Question 3

Which of the following statements about the endosymbiotic theory is correct?

Accepted Answer

It proposes that eukaryotic organelles such as mitochondria and chloroplasts originated from free-living prokaryotes that were engulfed by ancestral eukaryotic cells.

Question 4

A microbiologist is attempting to isolate a single bacterial species from a mixed culture. Which technique should they use, and what is the primary goal of this method?

Accepted Answer

Streak plate technique; to obtain isolated colonies for pure culture.

Question 5

Which of the following best explains why immersion oil is used with the 100x objective lens in bright field microscopy?

Accepted Answer

Immersion oil increases the refractive index between the specimen and the lens, reducing light refraction and increasing resolution. The resolution ($$R) is $$given by $$R = \frac{\lambda}{2NA}$$, where $$\lambda is $$the wavelength and $$NA is $$the numerical aperture.

Question 6

A bacterial cell is placed in a hypertonic solution. Predict the outcome and explain the process involved.

Accepted Answer

Water will move out of the cell by osmosis, causing plasmolysis (cell shrinkage).

Question 7

Which of the following is a key difference between prokaryotic and eukaryotic ribosomes, and how does this support the endosymbiotic theory?

Accepted Answer

Prokaryotic ribosomes are 70S, while eukaryotic cytoplasmic ribosomes are 80S; mitochondria and chloroplasts have 70S ribosomes, supporting their prokaryotic origin.

Question 8

A patient develops a healthcare-acquired infection (HAI) after surgery. Which of the following best describes the likely cause and prevention strategy?

Accepted Answer

The infection was likely caused by opportunistic pathogens introduced due to a breach in aseptic technique. Prevention involves strict adherence to aseptic procedures.

Question 9

Which of the following best describes the process of binary fission in prokaryotes?

Accepted Answer

A form of asexual reproduction where the cell duplicates its DNA, elongates, and divides into two genetically identical daughter cells.

Question 10

Which of the following statements about viral replication is correct?

Accepted Answer

Enveloped animal viruses typically enter host cells by fusion with the plasma membrane and acquire their envelope as they bud from the host cell.

Question 11

A scientist is studying a mutation that changes a codon from UAU (tyrosine) to UAA (stop codon). What type of mutation is this, and what is its likely effect on the protein?

Accepted Answer

Nonsense mutation; it introduces a premature stop codon, likely resulting in a truncated, nonfunctional protein.

Question 12

Which of the following best explains the difference between simple diffusion and facilitated diffusion across a prokaryotic plasma membrane?

Accepted Answer

Simple diffusion involves movement of molecules down their concentration gradient without the need for membrane proteins, while facilitated diffusion requires specific transport proteins but does not require energy.

Question 13

Which of the following best describes the function of a bacterial capsule and how it can be visualized?

Accepted Answer

A capsule is a polysaccharide-rich layer that protects bacteria from phagocytosis and can be visualized using negative staining.

Question 14

Which of the following statements about prions is correct?

Accepted Answer

Prions are infectious proteins that cause neurodegenerative diseases such as Creutzfeldt-Jakob disease and do not contain nucleic acids.

Question 15

A scientist is using Koch’s postulates to identify the etiological agent of a new disease. Which of the following is NOT a limitation of Koch’s postulates?

Accepted Answer

Koch’s postulates can always be applied to viruses because they grow on standard media.

Question 16

Which of the following best describes antigenic shift in influenza viruses and its impact on public health?

Accepted Answer

Antigenic shift is a major change in viral genome due to reassortment of gene segments, leading to new viral strains that can cause pandemics.

Question 17

Which of the following best explains the difference between mutualism and commensalism in host-microbe interactions?

Accepted Answer

Mutualism benefits both the host and the microbe, while commensalism benefits the microbe without affecting the host.

Question 18

A researcher observes a prokaryotic cell with a periplasmic space, thin peptidoglycan layer, and an outer membrane containing lipopolysaccharide. Which type of cell wall does this organism have?

Accepted Answer

Gram-negative cell wall.

Question 19

Which of the following best describes the role of reverse transcriptase in retrovirus replication?

Accepted Answer

Reverse transcriptase synthesizes complementary DNA (cDNA) from an RNA template, allowing integration into the host genome.

Comprehensive Study Notes: Microbiology Chapters 1, 3, 4, 5, and 6

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