Nokea
Which cells are responsible for antigen presentation to T cells?
- A. Plasma cells
- B. Antigen-presenting cells (APCs)
- C. NK cells
- D. Eosinophils
Correct Answer: B
Rationale: The correct answer is B: Antigen-presenting cells (APCs). APCs, such as dendritic cells, macrophages, and B cells, are specialized cells that capture, process, and present antigens to T cells to initiate an immune response. They express major histocompatibility complex (MHC) molecules for antigen presentation. Plasma cells (A) produce antibodies, NK cells (C) are involved in killing infected cells, and eosinophils (D) are primarily involved in parasitic infections and allergic responses, not antigen presentation to T cells.
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The immunoglobulin Joining chain (J-chain) is
- A. only produced by T-Cells
- B. only produced by neutrophils
- C. associated with only multimeric forms of IgM and IgA
- D. associated with IgE for histamine release
Correct Answer: C
Rationale: Step-by-step rationale:
1. The J-chain is a polypeptide involved in the formation of polymeric IgM and IgA.
2. Polymeric forms of IgM and IgA contain the J-chain, aiding in their multimeric structure.
3. The J-chain is not exclusive to T-cells or neutrophils, making choices A and B incorrect.
4. IgE is associated with FcεRI receptors for histamine release, so choice D is incorrect.
Summary:
The correct answer is C because the J-chain is specifically associated with the multimeric forms of IgM and IgA, helping to form their structure. Choices A, B, and D are incorrect as the J-chain is not solely produced by T-cells, neutrophils, or associated with IgE for histamine release.
The rearrangement of B cell antigen receptor genes occurs in
- A. Germinal centres
- B. Cortical areas of lymph nodes
- C. Bone marrow
- D. All secondary lymphoid organs
Correct Answer: C
Rationale: The rearrangement of B cell antigen receptor genes occurs in the bone marrow. This process involves the assembly of variable (V), diversity (D), and joining (J) gene segments to generate a diverse repertoire of B cell receptors. The bone marrow provides the necessary environment for this gene rearrangement to take place, ensuring the development of functional B cells. Germinal centers and cortical areas of lymph nodes are involved in B cell activation and differentiation, not gene rearrangement. While secondary lymphoid organs support B cell activation and immune responses, they are not specifically where the gene rearrangement occurs.
Which factor is primarily responsible for the division of bacterial populations into specific zones within sediments?
- A. predation by protozoans
- B. free oxygen availability
- C. competition for suitable electron acceptors
- D. cometabolism of organic compounds
Correct Answer: B
Rationale: The correct answer is B: free oxygen availability. In sediment environments, free oxygen availability plays a crucial role in determining bacterial population distribution due to oxygen gradients. Bacteria that require oxygen will be found in aerobic zones where oxygen is present, while anaerobic bacteria will thrive in zones with limited or no oxygen. This division is primarily responsible for the spatial organization of bacterial populations within sediments.
Choice A: Predation by protozoans is not primarily responsible for division of bacterial populations within sediments as it focuses on interactions between different organisms rather than the environmental factor of oxygen availability.
Choice C: While competition for suitable electron acceptors is important for microbial communities, it is not the primary factor responsible for the division of bacterial populations within sediments.
Choice D: Cometabolism of organic compounds refers to the metabolism of compounds alongside the primary substrate, and it is not directly related to the spatial distribution of bacterial populations within sediments based on oxygen availability.
Which cells are involved in innate immunity?
- A. B lymphocytes
- B. T lymphocytes
- C. Natural killer cells
- D. Plasma cells
Correct Answer: C
Rationale: The correct answer is C: Natural killer cells. Natural killer cells are part of the innate immune system and play a crucial role in identifying and destroying infected or abnormal cells. They are able to recognize and target cells that lack specific markers, providing a rapid response to infections.
Explanation for incorrect choices:
A: B lymphocytes are part of the adaptive immune system, not innate immunity.
B: T lymphocytes are also part of the adaptive immune system, not involved in innate immunity.
D: Plasma cells are differentiated B cells that produce antibodies in the adaptive immune response, not part of innate immunity.
Which complement protein is the main component of the Membrane Attack Complex (MAC)?
- A. C1
- B. C3
- C. C5b
- D. C4b
Correct Answer: C
Rationale: The correct answer is C: C5b. The Membrane Attack Complex (MAC) is formed by a sequence of complement proteins, with C5b playing a crucial role as the initiator. After C5b binds to the target cell membrane, it triggers the assembly of C6, C7, C8, and multiple C9 molecules to form the MAC pore. C1 (A) is the initiator of the classical pathway, not a component of the MAC. C3 (B) is involved in the formation of the C3 convertase and opsonization but is not the main component of the MAC. C4b (D) is part of the classical pathway and is involved in the formation of the C3 convertase, not the MAC.