openstax microbiology test bank

Correct Answer: B

Rationale: The correct answer is B: placenta. The placenta is a highly specialized structure that forms during pregnancy and serves as a barrier, protecting the fetus from harmful microorganisms that could potentially harm the developing baby. It facilitates the exchange of nutrients, oxygen, and waste between the mother and fetus while preventing the passage of most bacteria and viruses. The uterus (A) is the organ where the fetus develops, but it does not have the specific protective functions of the placenta. The vagina (C) is the birth canal and does not provide protection from microorganisms for the fetus. The mammary gland (D) is responsible for producing milk after birth and is not directly involved in protecting the fetus from microorganisms during pregnancy.

Correct Answer: C

Rationale: The correct answer is C: ELISA, Western blot. These tests are commonly used for diagnosing Lyme borreliosis due to their high sensitivity and specificity in detecting antibodies against Borrelia burgdorferi, the causative agent. ELISA is the initial screening test, while Western blot is used for confirmation. Widal agglutination test (A) is used for diagnosing typhoid fever, not Lyme disease. Cultivation on blood and chocolate agar (B) is not commonly used for diagnosing Lyme borreliosis as Borrelia species are difficult to culture. Ascoli thermoprecipitation test (D) is used for diagnosing pneumonia caused by Streptococcus pneumoniae, not Lyme disease.

Correct Answer: A

Rationale: Rationale: 1. Thin, pale pink microorganisms with spiral coils suggest Treponema pallidum, the causative agent of syphilis. 2. Staining with Romanovsky-Giemsa method highlights the characteristic morphology of T. pallidum. 3. Syphilis presents with various stages and symptoms, correlating with the lymph node involvement. 4. Leptospirosis is caused by Leptospira interrogans, presenting with different clinical features. 5. Relapsing fever is caused by Borrelia species, which do not match the description. 6. Trypanosomiasis is caused by Trypanosoma species, which have distinct morphology and staining properties.

Correct Answer: C

Rationale: The correct answer is C: genes with plasmid location. Clostridium tetani produces exotoxins through genes located on plasmids. Plasmids are extrachromosomal genetic elements that carry additional genes. These genes encode for the production of exotoxins in Clostridium tetani. Choices A, B, and D are incorrect because Clostridium tetani does produce exotoxins, it does not have only endotoxin activity, and the genes responsible for exotoxin production are located on plasmids, not solely on the chromosome or both chromosome and plasmid.

Correct Answer: B

Rationale: The correct answer is B: Plasmids. Plasmids are extrachromosomal DNA molecules found in bacteria that can replicate independently of the bacterial chromosome. They carry additional genetic information, such as antibiotic resistance genes or virulence factors. Mesosomes (choice A) are not involved in carrying genetic information; they are infoldings of the cell membrane. Ribosomes (choice C) are cellular organelles responsible for protein synthesis, not carriers of genetic information. Choice D is incorrect as plasmids are indeed extrachromosomal carriers of genetic information in bacteria.