Nokea
Phagocytosis is not a characteristic of which groups?
- A. protozoans
- B. algae
- C. fungi
- D. Archaea
Correct Answer: D
Rationale: Phagocytosis is a process where cells engulf and digest particles. Archaea lack membrane-bound organelles, including phagosomes, making phagocytosis impossible. Protozoans, algae, and fungi have the necessary cellular structures for phagocytosis. Therefore, the correct answer is D. Protozoans, algae, and fungi can perform phagocytosis due to their cellular structure and function, making choices A, B, and C incorrect.
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A structural domain essential for the assembly of the inflammasome is
- A. Leucine rich repeats
- B. TIR domain
- C. CARD
- D. All of the above
Correct Answer: C
Rationale: The correct answer is C: CARD. CARD stands for Caspase Activation and Recruitment Domain, which is crucial for the assembly of the inflammasome complex. It facilitates the recruitment and activation of caspase enzymes, leading to inflammatory responses. Leucine rich repeats (A) and TIR domain (B) are not directly involved in the assembly of the inflammasome. Therefore, the correct choice is C, as it specifically pertains to the structural domain essential for this process.
Multi-photon microscopy has proved to be an invaluable tool for the evaluation of the dynamics of immune responses in vivo. The following is a list of observations derived from intra-vital microscopy. Identify the incorrect statement.
- A. T cells make stable and prolonged contacts with APC presenting the specific antigen in the paracortex
- B. In the absence of antigens B cells move at the same speed and randomly in follicles
- C. In the presence of infection specific B cells quickly direct themselves towards the source of antigen
- D. Dendritic cells move rapidly through the germinal centre during an immune response
Correct Answer: D
Rationale: The correct answer is D because dendritic cells do not typically move rapidly through the germinal center during an immune response. Dendritic cells usually interact with T cells in the paracortex to present antigens, and they are not known to migrate rapidly through the germinal center.
A: This statement is correct as T cells do make stable and prolonged contacts with APCs in the paracortex during immune responses.
B: This statement is incorrect as B cells do not move at the same speed and randomly in follicles in the absence of antigens. They respond to signals and cues in the microenvironment.
C: This statement is correct as specific B cells can quickly direct themselves towards the source of antigen during an infection.
In summary, choice D is incorrect because dendritic cells do not move rapidly through the germinal center during an immune response, while the other choices accurately describe behaviors of immune cells during immune responses.
What is a key concept of the evolutionary arms race between hosts and pathogens?
- A. Both evolve to outcompete the other
- B. Pathogens evolve faster due to slow host mutation rates
- C. Hosts rely on chemical barriers rather than evolution
- D. Pathogens only evolve when hosts fail to adapt
Correct Answer: A
Rationale: Step 1: Evolutionary arms race involves a continuous cycle of adaptations by both hosts and pathogens to gain an advantage.
Step 2: Both parties strive to outcompete each other to survive and reproduce.
Step 3: This leads to a dynamic process where hosts evolve defense mechanisms while pathogens evolve ways to overcome them.
Step 4: Therefore, the key concept is that both hosts and pathogens evolve to outcompete each other in the evolutionary arms race.
Summary:
- Option B is incorrect as hosts can also evolve rapidly through mechanisms like recombination.
- Option C is incorrect as hosts do evolve through genetic changes, not just relying on chemical barriers.
- Option D is incorrect as pathogens continuously evolve strategies, not just when hosts fail to adapt.
Which of the following statements is NOT true?
- A. B cells are important in the defense against extracellular pathogens
- B. The number of memory B cells recognizing antigen X is always smaller than the number of naïve B cells recognizing antigen X, as most specific B cells are killed when the immune response subsides
- C. Memory B cells are B cells differentiated from cells that have encountered the antigen and are long-lived
- D. The B cell repertoire is virtually infinite and includes specificities for any possible antigen
Correct Answer: B
Rationale: The correct answer is B because the statement is false. Memory B cells are formed during an immune response and persist long-term, allowing for a faster and more robust response upon reinfection with the same antigen. The number of memory B cells recognizing an antigen is typically greater than the number of naïve B cells, as they are specifically primed and preserved. In contrast, naïve B cells are naive to the antigen and need to undergo activation and differentiation upon encountering the antigen for the first time. Therefore, statement B is incorrect as it inaccurately suggests that memory B cells are always fewer than naïve B cells recognizing the same antigen.
Thymocytes undergoing positive selection express:
- A. TCR
- B. CD4
- C. CD8
- D. All of the above
Correct Answer: D
Rationale: Thymocytes undergoing positive selection express both CD4 and CD8 co-receptors along with a functional T-cell receptor (TCR). CD4 and CD8 help in recognizing MHC molecules, while TCR is crucial for antigen recognition. Positive selection ensures that thymocytes with a functional TCR that can interact with self-MHC molecules survive. Therefore, the correct answer is D, as thymocytes undergoing positive selection express TCR, CD4, and CD8. Choice A, TCR alone, is incorrect as CD4 and CD8 are also expressed. Choices B and C are incorrect as positive selection involves the expression of both CD4 and CD8, not just one or the other.