Nokea
Neutrophils cannot
- A. Produce ROS
- B. Produce Defensins
- C. Produce NETs
- D. Present antigens to T cells
Correct Answer: D
Rationale: Neutrophils lack the ability to present antigens to T cells due to their short lifespan and absence of major histocompatibility complex (MHC) class II molecules. This process requires MHC class II presentation, which is typically done by antigen-presenting cells such as dendritic cells, macrophages, and B cells. Neutrophils primarily function in phagocytosis, releasing reactive oxygen species (ROS), defensins, and neutrophil extracellular traps (NETs) to combat pathogens. Thus, the correct answer is D. Other choices are incorrect because neutrophils are capable of producing ROS (A), defensins (B), and NETs (C).
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Which group(s) of microorganisms is (are) thought to be the oldest living organisms?
- A. eukaryotes
- B. heterotrophic prokaryotes
- C. Archaea
- D. viruses
Correct Answer: C
Rationale: The correct answer is C: Archaea. Archaea are thought to be the oldest living organisms due to their unique characteristics and genetic similarities to the earliest forms of life. They are known for thriving in extreme environments, resembling conditions on early Earth. Other choices are incorrect because eukaryotes are more complex and evolved later, heterotrophic prokaryotes came after autotrophic prokaryotes, and viruses are not considered living organisms.
Rolling circle replication refers to:
- A. DNA replication in every prokaryotic cell division
- B. DNA transfer during conjugation
- C. mitosis
- D. meiosis
Correct Answer: B
Rationale: Rolling circle replication is a mechanism commonly observed in DNA transfer during bacterial conjugation. The process involves the transfer of a single strand of DNA that acts as a template for the synthesis of a complementary strand in the recipient cell. This results in the formation of a circular DNA molecule in the recipient cell. This mechanism is distinct from the semiconservative replication seen in prokaryotic cell division (Choice A), the cell division process of mitosis (Choice C), and the reduction division of meiosis (Choice D). Rolling circle replication is specific to the transfer of genetic material between bacterial cells during conjugation, making Choice B the correct answer.
is a gaseous by-product of natural gas combustion plant hormone
- A. auxin
- B. Gibberellins
- C. Ethylene
- D. All above
Correct Answer: C
Rationale: The correct answer is C: Ethylene. Ethylene is indeed a gaseous plant hormone produced during the combustion of natural gas. It plays a crucial role in various plant processes such as fruit ripening, senescence, and stress responses.
A: Auxin is not a gaseous hormone and is primarily involved in promoting cell elongation and root growth.
B: Gibberellins are not gaseous hormones and mainly regulate plant growth processes like stem elongation and seed germination.
D: The statement "All above" is incorrect as auxin and gibberellins are not gaseous hormones, only ethylene fits the description.
Therefore, choice C, Ethylene, is the correct answer as it is the gaseous by-product of natural gas combustion and a plant hormone.
The differentiation of activated Th cells into various effector subsets depends mostly on:
- A. Signal 1 of activation
- B. The influence of polarizing cytokines secreted by dendritic cells
- C. Whether the T cell expresses CD4 or CD8
- D. The duration of signaling induced by TCR binding to peptide-MHC
Correct Answer: B
Rationale: The correct answer is B because polarizing cytokines secreted by dendritic cells play a crucial role in determining the differentiation of activated Th cells into specific effector subsets. These cytokines guide the Th cells towards different functional phenotypes, such as Th1, Th2, Th17, or Treg cells. This process helps tailor the immune response to the specific type of pathogen encountered. Choices A, C, and D are incorrect because while signal 1 of activation, T cell receptor co-receptors, and duration of signaling are important factors in T cell activation and differentiation, they do not have as direct and significant an impact on effector subset differentiation as the influence of polarizing cytokines.
The discovery of immunoglobulin gene rearrangement helped to explain:
- A. How the number of different immunoglobulins produced by an individual can be far greater than the number of genes in the human genome
- B. How the number of genes in the human genome can be far greater than the number of different immunoglobulins produced by an individual
- C. How thousands of immunoglobulin chains of different sequence may be produced by a single B cell
- D. Both A and C are correct
Correct Answer: A
Rationale: The correct answer is A: How the number of different immunoglobulins produced by an individual can be far greater than the number of genes in the human genome. Immunoglobulin gene rearrangement occurs during B cell development, leading to the generation of a diverse repertoire of antibodies from a limited number of genes. This process allows for the production of a vast array of immunoglobulins through mechanisms like V(D)J recombination. Choice B is incorrect because the gene rearrangement process actually enables a single gene to encode for multiple immunoglobulins. Choice C is partially correct but does not fully capture the significance of gene rearrangement in expanding the diversity of immunoglobulins beyond what the genome would suggest. Choice D is incorrect as it combines a correct statement (A) with an incomplete statement (C).