Which of the following statements regarding the antigenic shift is NOT true?

Correct Answer: D

Rationale: The correct answer is D because antigenic shift is a major change in the influenza virus where genetic material from different influenza viruses mix to create a new subtype. This is a large-scale change that results in a novel virus with a different antigenic composition. Option A and B are incorrect because antigenic shift does involve the exchange of genetic information between animal and human influenza A viruses, and it does occur when animal or avian influenza viruses of type A directly pass into the human population. Option C is incorrect because antigenic shift is not related to the recirculation of a previously circulating influenza strain.

Correct Answer: C

Rationale: To calculate the total magnification, we multiply the magnification of the ocular lens by the magnification of the objective lens. In this case, 10 (ocular) x 40 (objective) = 400. This is why choice C (400) is correct. Choices A, B, and D are incorrect because they do not represent the correct calculation of total magnification based on the given magnification powers of the ocular and objective lenses.

Correct Answer: D

Rationale: The correct answer is D: Erysipeloid. Erysipeloid is a bacterial infection caused by Erysipelothrix rhusiopathiae commonly found in animals like cattle. The patient's occupation as a cattle-ranch worker puts them at risk for this infection. Symptoms such as high body temperature, severe headache, carbuncle on the forearm with edema, and regional lymphadenitis are typical of erysipeloid. Anthrax (A) is more associated with skin lesions and severe systemic symptoms. Carcinoma of skin (B) presents differently with slow-growing skin lesions. Erysipelas (C) is a different bacterial infection characterized by red, swollen patches on the skin.

Correct Answer: D

Rationale: The correct answer is D: III, IV, V. 1. RNA viruses belong to Group III of the Baltimore classification system because their genetic material is single-stranded RNA. 2. They are also categorized under Group IV as they use reverse transcriptase to replicate their genetic material. 3. Finally, RNA viruses fall under Group V as they have an envelope derived from the host cell membrane. Therefore, options A, B, and C are incorrect as they do not include all the correct groups that RNA viruses belong to according to the Baltimore classification system.

Correct Answer: A

Rationale: The correct answer is A: Icosahedral structures. Icosahedral symmetry is commonly found in viruses due to its efficient way of packing genetic material. The icosahedron has 20 equilateral triangular faces, making it ideal for viral capsids. The other choices, B: Hexahedral, C: Tetrahedral, and D: Dodecahedral structures, do not accurately describe the cubic type of symmetry seen in viruses. Hexahedral refers to a six-faced polyhedron, tetrahedral to a four-faced polyhedron, and dodecahedral to a twelve-faced polyhedron, none of which align with the structure commonly observed in viruses.

Correct Answer: A

Rationale: The Burri-Gins staining technique is used to identify the presence of capsules around bacteria. Capsules are protective structures that some bacteria produce to evade the immune system. This technique stains the capsule, making it visible under a microscope. Therefore, the correct answer is A: Capsule formation. Incorrect: B: Spore formation - Spores are not typically identified using the Burri-Gins staining technique. C: Acid resistance - This property is not specifically identified by Burri-Gins staining. D: Alkali resistance - This property is not specifically identified by Burri-Gins staining.

Correct Answer: B

Rationale: The correct answer is B because humoral immunity involves the formation of specific antibodies by B cells. B cells differentiate into plasma cells that produce antibodies to target specific antigens. T cells are involved in cell-mediated immunity, not humoral immunity. Choice A is incorrect because T cells do not produce antibodies. Choice C is incorrect as only B cells are responsible for antibody production in humoral immunity. Choice D is incorrect as B cells play a crucial role in the humoral immune response.

Correct Answer: C

Rationale: The correct answer is C: ensure survival under harsh conditions. Bacterial endospores are dormant, resistant structures that form under adverse conditions to protect the bacterial DNA and allow the bacterium to survive extreme environments. This function is crucial for the bacterium's long-term survival. Choice A is incorrect as endospores do not directly produce exotoxins. Choice B is incorrect as endospores do not store nutrients but rather protect the bacterium's genetic material. Choice D is incorrect as endospores do not enhance motility but rather enable survival during unfavorable conditions.

Correct Answer: B

Rationale: Correct Answer: B - Plasmids are circular DNA molecules Rationale: 1. Plasmids are extrachromosomal DNA molecules found in bacteria. 2. Plasmids are typically circular in structure, not linear. 3. Circular plasmids are easily replicated and transferred between bacteria. 4. Plasmids can carry genes for antibiotic resistance, making option C incorrect. 5. Not all bacteria have plasmids, making option D incorrect. 6. While plasmids can provide benefits, they are not essential for bacterial survival, making option A incorrect.