Viral capsomeres are composed of subunits called

Correct Answer: B

Rationale: The correct answer is B: protomeres. Viral capsomeres are the building blocks of viral capsids, which are protein coats that enclose and protect the viral genetic material. These capsomeres are made up of smaller subunits called protomeres. Envelopes (A) refer to a lipid membrane surrounding some viruses, not the subunits of capsomeres. Capsids (C) are the protein coats that capsomeres make up, not the subunits themselves. Nucleoids (D) are found in bacterial cells and refer to the region where the genetic material is located, not the subunits of viral capsomeres.

Correct Answer: B

Rationale: The correct answer is B: Mycobacterium tuberculosis. Acid-fast bacteria have a unique cell wall component called mycolic acid, making them resistant to decolorization by acid-alcohol during staining. Mycobacterium tuberculosis is acid-fast, as it retains the stain due to its high lipid content. Streptococcus pyogenes (A), Clostridium perfringens (C), and Bacillus subtilis (D) do not possess mycolic acid in their cell walls, so they are not acid-fast.

Correct Answer: D

Rationale: The correct answer is D: Lamblia. The cysts described match the characteristics of Giardia lamblia, a protozoan parasite. Giardia cysts are oval-shaped, 50-60 microns in diameter, and contain 2 nuclei (macronucleus and micronucleus). Giardia is commonly found in contaminated water sources and can cause gastrointestinal illness in humans. Incorrect choices: A: Toxoplasma - Toxoplasma gondii is a parasite that causes toxoplasmosis, transmitted through ingestion of contaminated food or water, but its cysts do not match the description given in the question. B: Amoeba - Amoebas are single-celled organisms, but they do not typically form cysts with visible nuclei as described. C: Balantidium - Balantidium coli is a ciliated protozoan that can cause dysentery in humans, but its cysts do not

Correct Answer: B

Rationale: The correct answer is B: Sexual transmission. The symptoms described are indicative of a vaginal yeast infection caused by Candida albicans. The presence of large gram-positive oval oblong cells forming pseudomycelium is characteristic of Candida infection. Sexual transmission is the most probable channel of infection as Candida can be transmitted through sexual contact. Endogenous infection (A) refers to infections originating from the body's own flora, which is not the case here. Contact infection (C) typically involves direct physical contact or fomite transmission, which is less likely in this scenario. Vector-borne transmission (D) involves transmission through vectors like mosquitoes or ticks, which is not relevant in this case.

Correct Answer: B

Rationale: The correct answer is B: Biological oxidation. Haematrophic bacteria obtain energy through biological oxidation, where they break down organic compounds to generate ATP for cellular processes. This process involves the transfer of electrons from the substrate to an electron transport chain to produce energy. Heat production (A) is a byproduct of metabolism, not the primary way to obtain energy. In biosynthetic reactions (C), energy is utilized rather than generated. Cultivation in culture media (D) is a method of growing bacteria but does not directly provide energy. Therefore, the correct answer is B as it aligns with the metabolic process of haematrophic bacteria.

Correct Answer: D

Rationale: The correct answer is D: Fibers at the vertices of the icosahedron. Adenoviruses have fibers at the vertices of the icosahedron, which give them their distinctive pattern. These fibers help in attaching to host cells. Choices A, B, and C are incorrect because adenoviruses do not have a lipid envelope, helical capsid, or ssDNA. Adenoviruses have a non-enveloped icosahedral capsid and contain dsDNA. This makes choice D the correct answer as it specifically relates to the unique structural feature of adenoviruses.

Correct Answer: A

Rationale: The correct answer is A: Picornaviridae. Picornaviruses, such as enteroviruses, are commonly found in the feces of infected individuals. Therefore, their presence in water indicates fecal contamination and the need for additional purification. B: Herpesviridae are not typically associated with fecal contamination. C: Flaviviridae are mainly transmitted through arthropods like mosquitoes, not fecal contamination. D: Retroviridae, including HIV, are not typically excreted in high levels in feces and are not indicators of fecal contamination.

Correct Answer: B

Rationale: The correct answer is B: Gram negative coccobacillus. Bordetella pertussis, the causative agent of pertussis, is a gram-negative coccobacillus. This is because it is a small, rod-shaped bacterium that appears both as a bacillus (rod-shaped) and a coccus (spherical) shape. It does not retain the crystal violet stain in the Gram staining process, indicating its negative gram nature. Choice A is incorrect because pertussis is not a gram-positive bacillus. Choice C is incorrect because pertussis is not a long gram-negative rod-shaped bacterium. Choice D is incorrect as the other options do not accurately describe the morphology of Bordetella pertussis.

Correct Answer: C

Rationale: The correct answer is C: Obligate anaerobes. These bacteria cannot survive in the presence of oxygen as they lack the necessary enzymes to detoxify reactive oxygen species. Obligate aerobes (A) require oxygen, facultative anaerobes (B) can grow with or without oxygen, and aerotolerant anaerobes (D) can survive in the presence of oxygen but do not utilize it for growth.