Correct Answer: A

Rationale: The correct answer is A. Rubella virus has icosahedral type of symmetry due to its spherical shape with 20 faces. This symmetry allows for efficient packaging of genetic material and structural stability. Choice B is incorrect as rubella virus is an ssRNA virus, not ssDNA. Choice C is incorrect as rubella virus does have an envelope derived from the host cell membrane. Choice D is incorrect as rubella virus does have glycoprotein spikes on its surface that aid in host cell recognition and entry.

Correct Answer: A

Rationale: The correct answer is A: T-lymphocytes. In skin mycosis, a disorder of cellular immunity indicates a deficiency in T-lymphocytes, which play a crucial role in cell-mediated immunity. T-lymphocytes are responsible for recognizing and destroying infected cells. Reduction in T-lymphocytes impairs the body's ability to fight fungal infections. Incorrect choices: B: Immunoglobulin G - Immunoglobulin G is involved in humoral immunity, not cellular immunity. C: Immunoglobulin E - Immunoglobulin E is typically associated with allergic responses, not cellular immunity. D: B-lymphocytes - B-lymphocytes are responsible for producing antibodies in humoral immunity, not directly involved in cell-mediated immunity.

Correct Answer: B

Rationale: The correct answer is B because bacteria synthesize enzymes with various nature and action. This is true because bacteria can produce a wide range of enzymes to carry out different functions such as metabolism, cell wall synthesis, and nutrient acquisition. Option A is incorrect because bacteria do not synthesize identical enzyme sets due to their diverse functions. Option C is incorrect as bacteria and viruses have distinct enzyme profiles. Option D is incorrect as viruses typically have a narrower range of enzymes compared to bacteria. Therefore, the variability in enzyme types and actions produced by bacteria supports the correctness of option B.

Correct Answer: A

Rationale: The correct answer is A: Entamoeba gingivalis. Firstly, it is important to note that Entamoeba gingivalis is commonly found in the oral cavity, specifically in carious cavities. Secondly, Entamoeba gingivalis belongs to the Sarcodina class, which is characterized by their amoeboid movement using pseudopods. This protozoa is associated with oral health issues, particularly in individuals with poor oral hygiene. Now, let's analyze why the other choices are incorrect: B: Entamoeba histolutica is known for causing amoebic dysentery, not commonly associated with oral cavities. C: Entamoeba coli is typically found in the human large intestine, not in oral cavities. D: Amoeba proteus is a free-living amoeba commonly used in laboratory studies and not typically associated with oral cavity infections.

Correct Answer: A

Rationale: The correct answer is A. Rubella virus has icosahedral type of symmetry due to its spherical shape with 20 faces. This symmetry allows for efficient packaging of genetic material and structural stability. Choice B is incorrect as rubella virus is an ssRNA virus, not ssDNA. Choice C is incorrect as rubella virus does have an envelope derived from the host cell membrane. Choice D is incorrect as rubella virus does have glycoprotein spikes on its surface that aid in host cell recognition and entry.