Question 1

Which of the following best describes the primary function of the membrane attack complex (MAC) in the complement system?

Accepted Answer

To induce lysis of target cells by forming pores in their membranes

Question 2

Which complement component acts as the major opsonin, facilitating phagocytosis of microbes?

Accepted Answer

C3b

Question 3

A patient with a genetic deficiency in C1q would have impaired activation of which complement pathway?

Accepted Answer

Classical pathway

Question 4

Which of the following is the correct sequence of events in the classical pathway of complement activation?

Accepted Answer

C1q binds antigen-antibody complex → C4 and C2 cleavage → C3 convertase formation → C3 cleavage

Question 5

Which of the following fragments acts as a chemoattractant for neutrophils during inflammation?

Accepted Answer

C5a

Question 6

The alternative pathway of complement activation is initiated by:

Accepted Answer

Recognition of foreign cell-surface constituents such as lipopolysaccharide

Question 7

Which of the following best explains why the complement system is considered a cascade?

Accepted Answer

Each step amplifies the response by activating multiple downstream components

Question 8

A researcher adds purified C3b to a bacterial culture and observes increased phagocytosis by neutrophils. This effect is best explained by which biological function of the complement system?

Accepted Answer

Opsonization

Question 9

Which of the following equations correctly represents the formation of the classical pathway C3 convertase?

Accepted Answer

$$C4b + C2a \rightarrow C4b2a$$

Question 10

Which of the following statements about the lectin pathway is correct?

Accepted Answer

It uses MBL to recognize mannose residues on microbial surfaces

Question 11

A patient with a deficiency in Factor D would have impaired formation of which complex in the alternative pathway?

Accepted Answer

C3bBb

Question 12

Which of the following best describes the role of properdin (Factor P) in the alternative pathway?

Accepted Answer

It stabilizes the C3 convertase complex

Question 13

Which of the following is a unique feature of the classical pathway compared to the alternative and lectin pathways?

Accepted Answer

Activation by antigen-antibody complexes

Question 14

Which complement component is directly responsible for initiating the assembly of the membrane attack complex (MAC)?

Accepted Answer

C5b

Question 15

A bacterial infection triggers the release of C5a. What is the most likely effect of this event?

Accepted Answer

Recruitment of neutrophils to the site of infection

Question 16

Which of the following best explains why deficiencies in complement components can lead to increased susceptibility to infections?

Accepted Answer

Impaired opsonization and reduced lysis of pathogens

Question 17

Which of the following equations represents the formation of the alternative pathway C5 convertase?

Accepted Answer

$$C3bBb + C3b \rightarrow C3bBbC3b$$

Question 18

Which of the following is NOT a function of the complement system?

Accepted Answer

Activation of T cell receptors

Question 19

A mutation prevents the production of C3. Which of the following outcomes is most likely?

Accepted Answer

Impaired formation of both C3 and C5 convertases

Question 20

Which of the following best describes the role of C3a in the immune response?

Accepted Answer

Acts as a chemoattractant for eosinophils

Complement System: Structure, Function, and Activation Pathways

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