Which of the following is NOT a feature of T cells?

Correct Answer: A

Rationale: The correct answer is A because T cells do not recognize three-dimensional structures of a pathogen. T cell receptors interact with processed antigen fragments presented by MHC molecules on antigen-presenting cells. Choice B is correct because T cell receptors possess specificity for antigens. Choice C is incorrect because T cell receptors have multiple antigen-binding sites. Choice D is incorrect as T cell receptors can be secreted as soluble forms.

Correct Answer: C

Rationale: The correct answer is C: 1-b, 2-d, 3-a, 4-c. 1. The first match should be b, as it aligns with the order given. 2. The second match should be d, as it aligns with the order given. 3. The third match should be a, as it aligns with the order given. 4. The fourth match should be c, as it aligns with the order given. Therefore, option C is the correct match based on the given order. Other choices are incorrect because they do not align with the given order of matches.

Correct Answer: B

Rationale: The correct answer is B: Passive natural immunity occurs. This type of immunity is achieved through the transfer of antibodies (IgG) from the mother to the fetus during pregnancy. The antibodies provide protection to the newborn for the first few months of life. It is considered passive because the newborn is not actively producing the antibodies themselves. A: Active natural immunity occurs when the body produces its antibodies in response to exposure to an antigen. This is not the case for newborns receiving maternal IgG. C: Active artificial immunity occurs when the body is intentionally exposed to an antigen, such as through vaccination, to stimulate an immune response. This is not relevant to the scenario described. D: Passive artificial immunity occurs when pre-formed antibodies are transferred to an individual through a medical intervention, such as receiving immune globulin. This is not applicable to the situation of maternal transmission of IgG to newborns.

Correct Answer: B

Rationale: The correct answer is B: mycoplasmas. Mycoplasmas have cell walls, which contain peptidoglycan, making them structurally similar to typical bacteria. Algae (choice A) have cell walls made of cellulose, Gram-positive bacteria (choice C) have cell walls containing thick layers of peptidoglycan, and fungi (choice D) have cell walls made of chitin. Mycoplasmas lack a cell wall, but they have a flexible cell membrane that provides them with shape and protection.

Correct Answer: D

Rationale: The correct answer is D: Desulfovibrio. Archaea are distinguished by their unique 16S ribosomal RNA sequences and cell wall composition. Desulfovibrio belongs to the Archaea domain due to its 16S rRNA sequence similarity and lack of peptidoglycan in the cell wall. Halobacterium, Methanococcus, and Sulfolobus are all classified as Archaea based on these criteria, making them incorrect choices.