In which phase of mitosis do the chromatids separate?

Correct Answer: C

Rationale: In anaphase, sister chromatids separate and move towards opposite poles of the cell. This is facilitated by the shortening of microtubules attached to the centromeres. Prophase is the phase where chromosomes condense and the nuclear envelope breaks down. Metaphase is when chromosomes align at the metaphase plate. Telophase is when the nuclear envelope reforms and chromosomes decondense. Therefore, anaphase is the correct phase for chromatid separation.

Correct Answer: A

Rationale: The correct answer is A: Mycoplasma pneumoniae. Mycoplasma pneumoniae is a common cause of atypical pneumonia and is known to be resistant to beta-lactam antibiotics. The description of microorganisms forming microscopic colonies with a dense center resembling fried eggs is characteristic of Mycoplasma pneumoniae colonies seen on special media. Summary of other choices: B: Klebsiella pneumoniae is not typically associated with atypical pneumonia and does not exhibit the described colony morphology. C: Streptococcus pneumoniae is not resistant to beta-lactam antibiotics and does not produce colonies with the described appearance. D: Legionella pneumophila is associated with Legionnaires' disease, not atypical pneumonia, and does not form colonies resembling fried eggs.

Correct Answer: C

Rationale: The correct answer is C: fungi. Both penicillin and cephalosporin are produced by certain species of fungi. Penicillin is derived from the Penicillium fungi, while cephalosporin is produced by Cephalosporium fungi. Fungi have the ability to synthesize these antibiotics as part of their defense mechanisms against other microorganisms. Algae (A), slime molds (B), and protozoans (D) do not have the capability to produce antibiotics like penicillin and cephalosporin. Algae are mainly photosynthetic organisms, slime molds are protists that lack the ability to synthesize complex antibiotics, and protozoans are single-celled eukaryotic organisms that do not produce antibiotics like fungi do.

Correct Answer: D

Rationale: The correct answer is D: Multiplies by binary fission. Bacterial cells reproduce through binary fission, where a single cell divides into two identical daughter cells. This process is essential for bacterial growth and multiplication. A: The oxidative phosphorylation does not take place in the mitochondria of bacterial cells but in the cell membrane. B: Capsules are not organelles but outer protective layers found in some bacterial cells. C: Bacterial cells contain both DNA and RNA, essential for their genetic information and protein synthesis.

Correct Answer: A

Rationale: The correct answer is A, proportion 4:1. Gram (+) bacteria have a higher ratio of MG-ribonucleate to Mg. deoxyribonucleate because ribosomal RNA is more abundant in actively growing bacterial cells. This higher proportion of MG-ribonucleate to Mg. deoxyribonucleate is essential for protein synthesis and growth. The other choices are incorrect because they do not reflect the higher ratio of ribosomal RNA to DNA in Gram (+) bacteria, which is crucial for their metabolic activities and cellular functions.

Correct Answer: A

Rationale: The correct answer is A: Type IV hypersensitivity reaction. This type of reaction is characterized by a delayed response involving T cells. In this case, the appearance of a papule after 48 hours indicates a delayed hypersensitivity reaction, which is typical of a Type IV reaction. The other choices are incorrect because: B: Arthus phenomenon is a localized immune complex-mediated reaction, not seen in tuberculin tests. C: Seroreaction typically involves antibodies reacting with soluble antigens, not seen in this scenario. D: Type II hypersensitivity reactions involve antibodies targeting specific cells or tissues, which is not the mechanism at play in this case.

Correct Answer: A

Rationale: The correct answer is A because it lists the genera that belong to the family Reoviridae accurately. Orthoreovirus and Rotavirus are well-known genera within the family Reoviridae. Orbivirus is another genus belonging to the same family. Choice B is incorrect because Orthoretrovirus and Retrovirus are not part of the Reoviridae family. Orbfiloviridae is also not a valid genus within this family. Choice C is incorrect because Orthoretrovirus and Retrovirus are not part of the Reoviridae family. Orbivirus is the correct genus but the other two are inaccurate. Choice D is incorrect because Orthoretrovirus and Retrovirus are not part of the Reoviridae family. Orbarenaviridaefiloviridae is not a valid genus within Reoviridae.

Correct Answer: A

Rationale: The correct answer is A: Teratogenesis. Teratogenesis refers to the process of abnormal development of the fetus leading to congenital defects due to exposure to harmful agents during pregnancy. In this case, toxoplasmosis infection during pregnancy can lead to teratogenesis, causing multiple congenital defects in the child. Other choices are incorrect because B: Cancerogenesis refers to the process of cancer formation, C: Recombination is a genetic process unrelated to congenital defects, and D: Chemical mutagenesis refers to mutations caused by chemical agents, not necessarily congenital defects.

Correct Answer: A

Rationale: The correct answer is A: Clostridium botulinum. This bacterium produces the botulinum neurotoxin, which causes paralysis by blocking the release of acetylcholine at neuromuscular junctions. Clostridium perfringens causes gas gangrene, not paralysis. Escherichia coli is associated with gastrointestinal infections, not paralysis. Staphylococcus aureus produces enterotoxins causing food poisoning, not paralysis. Therefore, Clostridium botulinum is the correct choice based on its well-known association with paralysis due to botulinum neurotoxin production.