Natural active immunity occurs during infection or disease. It is active because lymphocytes are activated by antigens or pathogen's surface

Correct Answer: A

Rationale: Rationale: Natural active immunity is indeed active because it involves the activation of lymphocytes by antigens during infection or disease. This process leads to the production of memory cells for long-lasting protection. This distinguishes it from passive immunity, where antibodies are transferred rather than produced by the individual's immune system. Therefore, choice A is correct. Choice B is incorrect because it contradicts the nature of natural active immunity. Choice C is incorrect as the statement is always true for natural active immunity. Choice D is incorrect as there is a correct answer among the given choices.

Correct Answer: C

Rationale: The correct answer is C: Direct transfer of DNA between two bacterial cells. In bacterial conjugation, genetic material is transferred directly from one bacterial cell to another through a conjugative pilus. This process involves physical contact between the cells, followed by the transfer of plasmid DNA or chromosomal DNA. This mechanism allows for the exchange of genetic information between bacteria, leading to genetic diversity. Explanation of why other choices are incorrect: A: DNA transfer via bacteriophage - Bacteriophage is a virus that infects bacteria and transfers its genetic material, but this is not the mechanism involved in bacterial conjugation. B: Uptake of naked DNA from the environment - This process is known as transformation, where bacteria take up free DNA from the environment, but it is not specific to bacterial conjugation. D: Binary fission - Binary fission is a form of asexual reproduction in bacteria where a single cell divides into two identical cells, and it is not related to the process

Correct Answer: A

Rationale: The correct answer is A: Anthrax. Anthrax is caused by the bacterium Bacillus anthracis, which can form spores that are highly resistant and can survive in the soil for long periods. These spores can remain dormant until they come into contact with a susceptible host, leading to infection. Diphtheria, viral hepatitis, and pertussis are caused by different types of pathogens (bacteria and viruses) that do not have the same ability to persist in soil as anthrax spores. Therefore, the causative agents of these diseases are less likely to exist in the soil for extended periods compared to anthrax spores.

Correct Answer: C

Rationale: The correct answer is C: E + S = P. This notation represents the interaction between an enzyme (E) and a substrate (S) resulting in a product (P). Enzymes facilitate chemical reactions by binding to substrates and converting them into products. Choice A is incorrect because it does not include the enzyme in the reaction. Choice B is incorrect as it involves two substrates binding to the enzyme, not a substrate converting to a product. Choice D is incorrect as it shows two substrates reacting to form a product without involvement of an enzyme. Thus, choice C accurately represents the process of enzymatic reactions involving enzymes, substrates, and products.

Correct Answer: A

Rationale: The correct answer is A: Acid resistance. Tuberculous bacilli are acid-fast bacilli, meaning they resist decolorization by acid-alcohol after staining with Ziehl-Neelsen stain. This property is due to the high lipid content in the cell wall of Mycobacterium tuberculosis. Alkali resistance (B) and alcohol resistance (C) are not specific properties of tuberculous bacilli. Capsule formation (D) is a characteristic of some bacteria but is not a defining feature of tuberculous bacilli.

Correct Answer: A

Rationale: The correct answer is A: Actinomycosis. This is a chronic bacterial infection caused by Actinomyces species. In this case, the description of dense yellow-green colored focus, white granules in purulent masses, and presence of fungal druses, plasma cells, xanthome cells, and macrophages all match the characteristics of actinomycosis. Actinomycosis typically presents with abscess formation containing sulfur granules, which are yellowish and granular. The other choices (B: Furuncle, C: Carbuncle, D: Syphilis) do not fit the clinical and histological features described in the question, making them incorrect options.

Correct Answer: C

Rationale: The correct answer is C: Protection against harsh conditions. Bacterial endospores are dormant structures produced by certain bacteria as a survival strategy under unfavorable conditions. They protect the bacterial DNA and other essential components from damage caused by heat, chemicals, desiccation, and radiation. Endospores do not directly participate in energy production (A), DNA replication (B), or protein synthesis (D). These functions are carried out by the active, vegetative form of the bacterial cell.

Correct Answer: A

Rationale: Rationale: Natural active immunity is indeed active because it involves the activation of lymphocytes by antigens during infection or disease. This process leads to the production of memory cells for long-lasting protection. This distinguishes it from passive immunity, where antibodies are transferred rather than produced by the individual's immune system. Therefore, choice A is correct. Choice B is incorrect because it contradicts the nature of natural active immunity. Choice C is incorrect as the statement is always true for natural active immunity. Choice D is incorrect as there is a correct answer among the given choices.

Correct Answer: D

Rationale: The correct answer is D: Relenza and Tamiflu. Both Relenza and Tamiflu are anti-influenza drugs that target the neuraminidase enzyme of the influenza virus, thereby inhibiting its replication and spread. Maxi Grip (A) is not an anti-influenza drug, Theraflu (B) contains different active ingredients, and Amantadine and Rimantadine (C) target a different viral protein, M2 ion channel. Therefore, choices A, B, and C are incorrect as they do not specifically target neuraminidase for influenza treatment.