Bacteriophages reproduce by:

Correct Answer: D

Rationale: Bacteriophages are viruses that infect bacteria, not living organisms. They do not reproduce through division, mitosis, or meiosis because they lack the cellular machinery for these processes. Instead, bacteriophages replicate by inserting their genetic material into a host bacterium and hijacking its cellular machinery to produce new viral particles. Therefore, the correct answer is D - None of them. Division and mitosis involve cellular division in living organisms, while meiosis is a specialized process for sexual reproduction in eukaryotic organisms, none of which apply to bacteriophages.

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: B

Rationale: The optochin sensitivity test is used to differentiate Pneumococcal (Streptococcus pneumoniae) from other streptococci. Optochin sensitivity is a characteristic feature of Pneumococcal, as it inhibits its growth. The test involves placing optochin discs on a culture plate and observing the zone of inhibition around the disc for Pneumococcal. Neisseria gonorrhoeae, Staphylococci, and Group A streptococci do not exhibit optochin sensitivity, making them incorrect choices. In summary, the optochin sensitivity test is specific to Pneumococcal, making choice B the correct answer.

Correct Answer: A

Rationale: The correct answer is A: Triatomine bug. Triatomine bugs, also known as "kissing bugs," are the specific carrier of the trypanosomes that cause Chagas disease. These bugs transmit the parasite through their feces, which contain the infectious forms of the trypanosomes. When the bug bites a human or animal, it defecates near the bite wound, allowing the parasites to enter the bloodstream through the broken skin. Mosquitoes (B) transmit diseases like malaria and dengue fever, not Chagas disease. Tsetse flies (C) are known for transmitting African trypanosomiasis (sleeping sickness), not Chagas disease. Cockroaches (D) are not known to transmit Chagas disease.

Correct Answer: A

Rationale: The correct answer is A: Gp120. Gp120 is a glycoprotein on the surface of the HIV virus that specifically binds to the CD4 receptor on target cells. This binding is essential for the virus to enter the host cell and initiate the infection process. Gp41 is another glycoprotein on the virus that helps with membrane fusion, not binding to CD4. Gp32 and Gp55 are not involved in the specific binding of HIV to CD4 molecules. So, A is correct as it directly plays a key role in the initial attachment of HIV to target cells.

Correct Answer: B

Rationale: The correct answer is B: Clostridium tetani. Endospores are formed by certain bacteria as a survival mechanism in harsh conditions. Clostridium species, including C. tetani, have the ability to form endospores. Staphylococcus aureus (A), Neisseria gonorrhoeae (C), and Escherichia coli (D) do not produce endospores. Staphylococcus aureus is a gram-positive cocci bacterium, Neisseria gonorrhoeae is a gram-negative diplococci bacterium, and Escherichia coli is a gram-negative rod-shaped bacterium. Therefore, the correct choice is Clostridium tetani as it is known for its ability to form endospores.

Correct Answer: C

Rationale: The correct answer is C because bacteriocins are substances with protein nature, not polysaccharides. Bacteriocins are antimicrobial peptides that kill bacterial cells, mainly those of closely related species or other strains of the same species. Polysaccharides are not typically involved in bacteriocin activity. Therefore, option C is false. Options A, B, and D are true statements supported by the nature and function of bacteriocins.

Correct Answer: B

Rationale: The correct answer is B: homeostasis. Homeostasis refers to the process by which living organisms maintain a stable internal environment despite external changes. It involves various biological processes and mechanisms that regulate factors such as temperature, pH, and nutrient levels within narrow limits. This is crucial for the proper functioning of cells, tissues, and organs. Now, let's analyze the other choices: A: Infection - Infection refers to the invasion and multiplication of harmful microorganisms in the body, leading to illnesses. It is not the correct answer as it does not encompass the overall maintenance of internal conditions. C: Immunity - Immunity is the body's ability to resist and fight off infections. While immunity is related to defense against foreign agents, it does not fully capture the concept of maintaining internal stability. D: Commensalism - Commensalism is a type of symbiotic relationship between different species where one benefits without harming the other. It is not related to the overall regulation of

Correct Answer: A

Rationale: The correct answer is A: 20 minutes. Escherichia coli has a short generation time, typically around 20 minutes. This means that under ideal conditions, one bacterium can divide and produce two daughter cells every 20 minutes. This rapid growth rate is a characteristic of E. coli and is important in various fields such as microbiology and biotechnology. Choice B (60 minutes) and Choice C (20 hours) are incorrect as they do not align with the typical generation time of E. coli. Choice D (24 hours) is also incorrect as it is too long for the generation time of E. coli.