Q: Which of the following equations correctly represents the calculation of the titer in an agglutination assay?

$\text{Titer} = \text{Reciprocal of the highest dilution of serum that still causes agglutination}$

Question 1

Which of the following best describes a Type I hypersensitivity reaction?

Accepted Answer

It is an antibody-mediated response involving IgE and rapid onset after exposure to an allergen.

Question 2

A patient receives an allergy shot containing increasing doses of a specific allergen over several months. What is the primary immunological mechanism behind this desensitization therapy?

Accepted Answer

Promotion of IgG 'blocking antibodies' that compete with IgE for allergen binding.

Question 3

Which of the following is an example of a Type III hypersensitivity reaction?

Accepted Answer

Post-streptococcal glomerulonephritis.

Question 4

A patient develops a red, indurated area at the site of a tuberculin skin test 48 hours after injection. Which type of hypersensitivity reaction is this, and what is the main immune cell involved?

Accepted Answer

Type IV; T lymphocytes

Question 5

Which of the following best explains the function of clavulanic acid in the antibiotic combination Augmentin?

Accepted Answer

It inhibits beta-lactamase enzymes, protecting amoxicillin from degradation.

Question 6

Which of the following equations correctly represents the calculation of the titer in an agglutination assay?

Accepted Answer

$	ext{Titer} = 	ext{Reciprocal of the highest dilution of serum that still causes agglutination}$

Question 7

Which of the following statements about the polymerase chain reaction (PCR) is correct?

Accepted Answer

PCR requires Taq DNA polymerase because it is heat-stable and can withstand the denaturation step at $95^\circ$C.

Question 8

Which of the following best describes the process of denitrification in the nitrogen cycle?

Accepted Answer

Conversion of nitrate to nitrogen gas by anaerobic bacteria.

Question 9

A hospital is deciding between using boiling, autoclaving, and pasteurization to sterilize surgical instruments. Which method is most effective for sterilization and why?

Accepted Answer

Autoclaving, because it uses pressurized steam at $121^\circ$C to kill all forms of microbial life including spores.

Question 10

Which of the following is a major advantage of using recombinant vaccines over whole-agent vaccines?

Accepted Answer

Recombinant vaccines are safer because they do not contain the entire pathogen, reducing the risk of infection.

Question 11

A patient is diagnosed with AIDS. Which of the following laboratory findings is most consistent with this diagnosis?

Accepted Answer

CD4+ T cell count below 200 cells/mm$^3$ and presence of AIDS-defining illnesses.

Question 12

Which of the following best explains why the ELISA (enzyme-linked immunosorbent assay) is a sensitive method for detecting specific antibodies in a patient's serum?

Accepted Answer

It uses an enzyme-linked secondary antibody that produces a color change when the substrate is added, allowing detection of even small amounts of antibody.

Question 13

Which of the following is the correct order of resistance to disinfectants, from most resistant to least resistant?

Accepted Answer

Endospores > Mycobacteria > Gram-negative bacteria > Enveloped viruses

Question 14

Which of the following best describes the mechanism of action of quinine derivatives in treating malaria?

Accepted Answer

They disrupt the parasite's ability to detoxify heme, leading to toxic buildup within the parasite.

Question 15

A laboratory is using restriction endonucleases and T4 ligase in a cloning experiment. What is the primary function of T4 ligase in this process?

Accepted Answer

To join DNA fragments by forming phosphodiester bonds between adjacent nucleotides.

Question 16

Which of the following best explains why it is important to use antibiotics responsibly?

Accepted Answer

Responsible use of antibiotics reduces the risk of developing antibiotic-resistant bacteria.

Question 17

Which of the following is a key difference between direct and indirect ELISA?

Accepted Answer

Direct ELISA detects antigen using a labeled primary antibody, while indirect ELISA detects antibody using a labeled secondary antibody.

Question 18

Which of the following best describes the function of a vector in recombinant DNA technology?

Accepted Answer

A vector is a DNA molecule used to carry foreign genetic material into a host cell.

Question 19

A patient presents with fever, chills, and a black eschar after handling animal hides. Which microorganism is most likely responsible, and what is the most probable route of infection?

Accepted Answer

Bacillus anthracis; cutaneous

Question 20

Which of the following best explains why the smallpox vaccine is effective in eradicating the disease?

Accepted Answer

The vaccine is a live attenuated virus that induces strong, long-lasting immunity and there are no animal reservoirs for smallpox.

Comprehensive Study Notes: unit 4

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