Which of the following bacteria is responsible for producing a neurotoxin that causes tetanus?

Correct Answer: B

Rationale: The correct answer is B: Clostridium tetani. Clostridium tetani produces tetanospasmin, a neurotoxin causing tetanus. It enters the body through wounds and affects the nervous system. A: Clostridium botulinum produces botulinum toxin causing botulism, not tetanus. C: Streptococcus pneumoniae causes pneumonia, not tetanus. D: Mycobacterium tuberculosis causes tuberculosis, not tetanus.

Correct Answer: A

Rationale: The correct answer is A: Protozoa. Protozoa are single-celled eukaryotic organisms, meaning they have a nucleus and other membrane-bound organelles. Eukaryotes have complex cellular structures that include a nucleus, mitochondria, and other organelles. Therefore, protozoa are eukaryotes. Viruses (B) are not considered cells and lack cellular structures. Viroids (C) are smaller infectious agents that consist of only RNA, lacking the cellular structure of eukaryotes. Prions (D) are infectious proteins and do not possess cellular structures like eukaryotes. So, protozoa are the only choice that relates to eukaryotes due to their cellular structure.

Correct Answer: B

Rationale: The correct answer is B because anaerobic bacteria can grow in environments without oxygen. Anaerobic bacteria do not require oxygen for their metabolism and energy production. They can thrive in oxygen-deprived conditions by using alternative electron acceptors. Choice A is incorrect because anaerobic bacteria do not require oxygen to survive. Choice C is incorrect because anaerobic bacteria typically cannot survive in the presence of high concentrations of oxygen. Choice D is incorrect because anaerobic bacteria do not perform photosynthesis.

Correct Answer: A

Rationale: The correct answer is A: Toxoplasmosis. Toxoplasmosis is a parasitic infection caused by Toxoplasma gondii, which can be transmitted to humans through contact with infected cat feces. During pregnancy, Toxoplasma infection can result in severe birth defects such as microcephaly and mental retardation in the child. In this case, the presence of a cat in the family and the child's abnormalities suggest a possible link to Toxoplasmosis. Other choices are incorrect because: B: Leishmaniasis is a parasitic disease transmitted by sandflies and does not typically cause the specific birth defects mentioned in the scenario. C: Dysentery is a bacterial infection that primarily affects the intestines and does not cause the neurological abnormalities described. D: Balantidiasis is a parasitic infection caused by Balantidium coli, a ciliated protozoan, but it is not associated with

Correct Answer: A

Rationale: Step-by-step rationale for choice A: 1. Viruses contain genetic material in the form of nucleic acids (DNA or RNA). 2. Proteins are essential for the structure and function of viral particles. 3. Nucleic acids (genetic material) and proteins are the two main components of viruses. 4. Therefore, choice A (nucleic acid and proteins) is correct. Summary: - Choice B (nucleic acids and lipids) is incorrect as lipids are not a main structural component of viruses. - Choice C (lipids and proteins) is incorrect as nucleic acids are essential components of viruses. - Choice D (proteins and glycoproteins) is incorrect as glycoproteins are a type of protein and not a separate component in viruses.

Correct Answer: B

Rationale: The correct answer is B: genotype. The genotype refers to the actual genetic makeup of an organism, including all the genes and alleles present in its DNA. This determines the traits and characteristics of an organism. Phenotype (A) is the observable physical or biochemical characteristics of an organism. Conjugation (C) is a process in bacteria involving the transfer of genetic material. Construct (D) is not a term related to genetics. Therefore, the correct choice is B as it specifically refers to the genetic composition of an organism.

Correct Answer: A

Rationale: The correct answer is A: prions. Prions are misfolded proteins that can cause spongiform encephalopathy by inducing normal proteins to misfold as well. Prions lack genetic material, distinguishing them from viruses (B), bacteria (C), and fungi (D), which all contain genetic material and cannot directly cause spongiform encephalopathy through protein misfolding.

Correct Answer: D

Rationale: The correct answer is D: rabbit fever. Tularemia is commonly known as rabbit fever due to the fact that it is often contracted through handling infected rabbits or other rodents. This zoonotic disease is caused by the bacterium Francisella tularensis. Scarlet fever (A) is a streptococcal infection characterized by a rash, not related to tularemia. Strep throat (B) is a bacterial infection caused by Streptococcus bacteria and is not associated with tularemia. Cat scratch fever (C) is caused by Bartonella henselae and typically transmitted through cat scratches or bites, not related to tularemia.

Correct Answer: B

Rationale: The correct answer is B because the structure of the cytoplasmic membrane in gram-positive and gram-negative bacteria is fundamentally different. Gram-positive bacteria have a single-layered cytoplasmic membrane, while gram-negative bacteria have a double-layered cytoplasmic membrane with an additional outer membrane. This key difference is crucial for various functions such as antibiotic resistance and nutrient transport. Rationale for the incorrect choices: A: Gram-positive bacteria have a single-layered cytoplasmic membrane, not a double-layered one. C: Prokaryotes do have a cytoplasmic membrane, which is essential for maintaining cell integrity and regulating the passage of molecules. D: Gram-negative bacteria have a double-layered cytoplasmic membrane, not a three-layered one.