A scientist identifies a strand of RNA that can be directly used to code for important viral proteins during viral replication. What have they found?

Correct Answer: C

Rationale: The correct answer is C: (+RNA). This indicates that the scientist found a positive-sense RNA strand that can be directly translated by host cell machinery to produce viral proteins. Positive-sense RNA can act as messenger RNA, allowing immediate protein synthesis during viral replication. Choice A (RNA major) and D (RNA minor) are not standard terms used to describe RNA strands in virology. Choice B (-RNA) indicates a negative-sense RNA strand, which requires transcription to form a complementary positive-sense strand before protein synthesis. Thus, the identification of a strand of RNA that directly codes for viral proteins aligns with the characteristics of a positive-sense RNA strand.

Correct Answer: B

Rationale: The correct answer is B: Proteus mirabilis. This bacterium is known to cause urinary tract infections (UTIs) and matches the description given in the question. Proteus mirabilis is a gram-negative rod-like bacterium that forms greenish mucoid colonies with a specific smell due to its production of urease enzyme. This enzyme leads to the formation of struvite crystals, which can cause painful and frequent urination. Pseudomonas aeruginosa (A) is not typically associated with UTIs. E.coli (C) is the most common cause of UTIs but does not match the specific description provided. Str.pyogenes (D) is a gram-positive bacterium and is not typically associated with UTIs.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Warts are caused by human papillomavirus (HPV) due to its ability to infect the skin. 2. HPV infects the top layer of skin and causes the rapid growth of cells, leading to the formation of warts. 3. Herpesvirus (choice B) causes herpes, not warts. 4. HIV (choice C) weakens the immune system but does not directly cause warts. 5. Varicella-zoster virus (choice D) causes chickenpox and shingles, not warts. Summary: Choice A is correct as warts are primarily caused by HPV, which infects the skin cells. Choices B, C, and D are incorrect as they are associated with different viral infections that do not lead to the development of warts.

Correct Answer: A

Rationale: The correct answer is A: Homemade canned meat. Botulism is caused by the Clostridium botulinum bacteria, which thrives in low-oxygen environments like improperly canned food. Homemade canned meat poses a higher risk of contamination as it may not have been processed correctly, allowing the bacteria to grow and produce toxins. Custard pastry, sour cream, and strawberries are less likely to cause botulism as they are not typically associated with the bacteria unless improperly handled or stored. Homemade canned meat is the most probable cause based on the characteristic symptoms of botulism and the conditions that favor the growth of Clostridium botulinum in canned food.

Correct Answer: A

Rationale: The correct answer is Amebiasis. The patient's symptoms of abdominal pain, loose stools with mucus and blood, along with the presence of protozoa containing phagocytosed erythrocytes in stool analysis are indicative of Entamoeba histolytica infection. The size (30-40 microns) and pseudopodia characteristics match E. histolytica. Amebiasis commonly presents with dysentery, while Leishmaniasis (B) typically causes skin ulcers. Trichomoniasis (C) is a sexually transmitted infection, not associated with the described symptoms. Giardiasis (D) is characterized by foul-smelling diarrhea and steatorrhea, not bloody diarrhea as seen in this case.

Correct Answer: A

Rationale: The correct answer is A: Selective toxicity. Chemotherapy aims to target cancer cells while minimizing harm to healthy cells, known as selective toxicity. This principle is crucial to effectively treat cancer without causing excessive damage to the patient's body. Accumulation in the macroorganism (B) and causing allergies (C) are not fundamental principles of chemotherapy and can lead to harmful side effects. Therefore, the correct answer is A as it aligns with the core objective of chemotherapy.

Correct Answer: A

Rationale: The correct answer is A: Mantoux test. The Mantoux test is used to screen for tuberculosis by injecting PPD intradermally. The presence of a delayed hypersensitivity reaction indicates prior exposure to Mycobacterium tuberculosis. The Schick test (B) is used to test for immunity to diphtheria, while the Dick test (C) is used to test for immunity to scarlet fever. Therefore, the correct use of PPD is in the Mantoux test for tuberculosis screening.

Correct Answer: A

Rationale: The correct answer is A: TRUE. Poxviruses are indeed the largest viruses, ranging from 200-450 nm in size, which is close to the resolution limit of a light microscope. This makes them almost visible under a light microscope. The other choices are incorrect because poxviruses are not smaller or uncertain in size (choices B and C), nor are they partially visible - they are almost visible due to their relatively large size.

Correct Answer: A

Rationale: Step 1: Streptococcus pyogenes is commonly known as Group A Streptococcus, which is the primary bacteria responsible for causing strep throat. Step 2: Staphylococcus aureus is not typically associated with strep throat but can cause skin infections and other illnesses. Step 3: Neisseria gonorrhoeae is the bacteria responsible for gonorrhea, a sexually transmitted infection, not strep throat. Step 4: Clostridium tetani causes tetanus, a bacterial infection that affects the nervous system and is not related to strep throat.