A microscope that provides a three-dimensional image of a specimen is a

Correct Answer: D

Rationale: The correct answer is D: scanning electron microscope. A scanning electron microscope provides a three-dimensional image of a specimen by scanning a focused electron beam across the surface of the specimen, detecting the electrons that are emitted from the surface, and creating a detailed image. This is achieved through the detection of secondary electrons, backscattered electrons, and X-rays emitted from the specimen surface. A dark-field microscope (choice A) utilizes oblique lighting to enhance contrast and is not specifically designed to provide a 3D image. A transmission electron microscope (choice B) uses a beam of electrons transmitted through a specimen to create a 2D image at high magnification. A bright-field microscope (choice C) is a basic microscope that illuminates a specimen with uniform light and does not provide a 3D image like a scanning electron microscope does.

Correct Answer: B

Rationale: The correct answer is B: Protozoans. Protozoans lack a cyst stage, which is a protective, dormant stage that allows them to survive in harsh conditions outside the host. Without a cyst stage, protozoans must be transferred quickly between hosts to avoid exposure to unfavorable environments. Molds (A) are fungi that reproduce through spores and do not have a cyst stage like protozoans. Helminths (C) are parasitic worms that have complex life cycles involving different hosts but do not rely on a cyst stage for survival. Viruses (D) are not considered protozoans and do not have a cyst stage, but they are not classified as protozoans.

Correct Answer: C

Rationale: The correct answer is C: Escherichia coli. E. coli is the most common cause of acute cystitis. It typically presents with leukocytes and gram-negative bacilli in the urine. The green pigment production indicates pyocyanin, which is a characteristic of E. coli. Pseudomonas aeruginosa (A) can also produce green pigment, but it is less common in urinary tract infections. Proteus mirabilis (B) is associated with a swarming motility pattern on agar, not mucous colonies. Klebsiella pneumoniae (D) is associated with pneumonia and other respiratory infections, not cystitis.

Correct Answer: B

Rationale: The correct answer is B because the main target of the toxin produced by Vibrio cholerae is the epithelial cells of the small intestine. This toxin, known as cholera toxin, binds to the surface of these cells and disrupts their normal function, leading to the characteristic watery diarrhea seen in cholera. The other choices are incorrect because macrophages are not the main target, RBCs are not directly affected by the toxin, and the stomach epithelial cells are not specifically targeted by Vibrio cholerae toxin.

Correct Answer: B

Rationale: The correct answer is B: ribosome. Ribosomes are responsible for protein synthesis, not packaging. The Golgi complex (A) processes and packages proteins. The rough endoplasmic reticulum (rER) (C) is involved in protein synthesis and transport. Lysosomes (D) contain enzymes for digestion, not protein packaging. Therefore, ribosomes are the organelle directly involved in protein synthesis, making it the correct choice.

Correct Answer: A

Rationale: The correct answer is A because it accurately describes the major morphological forms of bacteria. Cocci are spherical, rod-shaped bacteria are called bacilli, and curved bacteria are spirilla. Staphylococci, streptococci, and diplococci are specific types of cocci, not major morphological forms. Basicili and spiralis are not common morphological forms of bacteria. Option D is incorrect as the other choices do represent major morphological forms of bacteria.

Correct Answer: A

Rationale: The correct answer is A: 1 chromosome. Bacterial cells typically have a singular circular chromosome that contains their genetic material. This chromosome is essential for the cell's survival and contains all the necessary genetic information for its functions. Choices B, C, and D are incorrect because they refer to the chromosome numbers found in human cells (23 pairs or 46 individual chromosomes). Bacteria, being prokaryotic organisms, have a simpler genetic makeup compared to eukaryotic organisms like humans, hence they possess only one chromosome.

Correct Answer: C

Rationale: The correct answer is C: Ebola virus. The patient's symptoms align with Ebola virus infection, including fever, severe hemorrhagic syndrome, and CNS involvement. Ebola virus is known to cause hemorrhagic fevers with high mortality rates. A: SARS CoV causes Severe Acute Respiratory Syndrome, which typically presents with respiratory symptoms, not hemorrhagic fever. B: Lymphocytic choriomeningitis virus usually causes a mild illness with flu-like symptoms, not severe hemorrhagic syndrome. D: ECHO 9 virus is associated with aseptic meningitis, not hemorrhagic fever.

Correct Answer: A

Rationale: The correct answer is A: anabolic. Anabolic reactions involve the synthesis of larger organic molecules from smaller precursor molecules. This process requires energy input and is essential for growth and repair in living organisms. Choice B: Catabolic reactions involve the breakdown of larger molecules into smaller ones, releasing energy in the process. This is the opposite of what is described in the question. Choice C: Metabolic is a broad term that encompasses all chemical processes in living organisms, including both anabolic and catabolic reactions. It is not specific to the assembly of small molecules into larger ones. Choice D: "Any of the above" is incorrect because only anabolic reactions specifically involve the assembly of small precursor molecules into larger organic molecules.