Which one of the following statements about the cytoplasmic membrane of the prokaryotes is true?

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.

Correct Answer: B

Rationale: Step-by-step rationale: 1. Sodium is the major cation in the intracellular fluid. 2. It plays a crucial role in maintaining cell volume and transmitting nerve impulses. 3. Potassium is the major cation in the extracellular fluid, not intracellular. 4. Bicarbonate and sulfate are anions and not major cations in intracellular fluid. Summary: Choice B (sodium) is correct as it is the major cation in intracellular fluid, essential for various cellular functions. Choices A, C, and D are incorrect as potassium is extracellular, while bicarbonate and sulfate are anions and not predominant cations in intracellular fluid.

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: D

Rationale: The correct answer is D, Klebsiella pneumoniae. Klebsiella pneumoniae is a fermentative gram-negative rod, which means it can ferment sugars. In contrast, Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia are non-fermentative gram-negative rods. These organisms do not ferment sugars for energy production. Therefore, Klebsiella pneumoniae is the only fermentative organism among the choices, making it the correct answer.

Correct Answer: D

Rationale: The correct answer is D: Binary fission. Binary fission is a method of bacterial cell division, not a method of acquiring genetic material. Transformation, conjugation, and transduction are mechanisms through which bacteria can acquire genetic material from other sources. Transformation involves the uptake of naked DNA from the environment, conjugation is the transfer of genetic material through direct cell-to-cell contact, and transduction is the transfer of genetic material via bacteriophages. Therefore, binary fission is the only option that does not involve the acquisition of new genetic material.

Correct Answer: C

Rationale: The correct answer is C: Negative stain. Negative staining uses acidic dyes which are repelled by the bacterial cell wall components, highlighting bacteria with a large amount of peptidoglycan. Acid-fast stain (A) is used to identify Mycobacterium species with waxy cell walls. Gram stain (B) differentiates bacteria into Gram-positive and Gram-negative based on cell wall composition. Option D is a duplicate of option C and is incorrect.

Correct Answer: D

Rationale: The correct answer is D because enveloped viruses have a lipid bilayer envelope derived from the host cell membrane, which is a complex structure, not exhibiting any specific symmetry. Choice A (cubic symmetry) is incorrect as enveloped viruses do not have any specific geometric shape. Choice B (spiral symmetry) is incorrect as this type of symmetry is typically seen in non-enveloped viruses like helical viruses. Choice C (complex symmetry) is also incorrect as enveloped viruses do not exhibit a specific symmetrical pattern. Therefore, the correct answer is D because enveloped viruses do not have a defined symmetry and can vary in shape and structure.

Correct Answer: D

Rationale: The correct answer is D: Structure of cell wall. When studying a bacterial smear stained by the Ozheshko method, the focus is on the cell wall structure. This staining method highlights the cell wall morphology, allowing for detailed examination. Flagella, spores, and capsules are not typically visualized using this staining method. Flagella require special staining techniques, spores are usually observed through specific staining methods like Schaeffer-Fulton, and capsules are not easily visualized with the Ozheshko staining method. Therefore, the structure of the cell wall is the most relevant feature to study in this context.

Correct Answer: A

Rationale: The correct choice is A: Binding to IgE fixed to mast cells. The Besredka desensitization method involves injecting small, gradually increasing doses of the allergen to induce tolerance and prevent anaphylactic shock. This process works by binding the allergen to IgE antibodies fixed to mast cells, which prevents the release of histamine and other inflammatory mediators that trigger allergic reactions. This desensitization process helps the immune system become less reactive to the allergen over time. Incorrect choices: B: Inhibited synthesis of mast cells mediators - This choice does not reflect the mechanism of the Besredka desensitization method, which involves binding to IgE on mast cells. C: Stimulation of the immunological antigen tolerance - While this may sound plausible, the Besredka method specifically targets the IgE-mast cell interaction. D: Stimulation of antigen-specific IgG synthesis - While IgG antibodies may play a role in desensitization, the