Which of the statements is false:

Correct Answer: A

Rationale: The correct answer is A because spirochaetes are not bacilli; they are spiral-shaped bacteria. Bacilli are rod-shaped bacteria, making statement A false. Statement B is true as diplococci are spherical bacteria occurring in pairs. Statement C is true as rod-shaped bacteria have one diameter longer than the other. Statement D is true as coccobacilli are short, oval-shaped bacteria resembling cocci and rods. In summary, spirochaetes are spiral-shaped, not bacilli, making statement A false.

Correct Answer: B

Rationale: The correct answer is B: mitochondria. Stroma is a component of chloroplasts, not mitochondria. Lysosomes contain hydrolytic enzymes, not stroma. Mitochondria have an inner and outer membrane structure, with the matrix containing the stroma where important metabolic processes occur. This is where the Krebs cycle and oxidative phosphorylation take place. Stroma in chloroplasts is where photosynthesis occurs. So, the correct answer is B because stroma is a component of mitochondria, where crucial energy production processes happen.

Correct Answer: A

Rationale: Polyclonal antibodies are produced by different B cells, each recognizing a different epitope on an antigen. Therefore, they can respond to multiple antigens. This diversity in recognition allows polyclonal antibodies to bind to various targets, making option A true. Options B, C, and D are incorrect as they do not accurately reflect the nature of polyclonal antibodies' ability to recognize multiple antigens.

Correct Answer: A

Rationale: The correct answer is A: Clostridium perfringens. Clostridium perfringens is known to cause gas gangrene and is a Gram-positive rod that produces spores and gas in tissue infections. Clostridium tetani causes tetanus, not gas gangrene. Bacillus anthracis causes anthrax, not gas gangrene. Staphylococcus aureus is a Gram-positive cocci and does not produce spores or gas in the context of gas gangrene. Therefore, based on the characteristics of the microorganism isolated from the wound sample, Clostridium perfringens is the most likely causative agent.

Correct Answer: B

Rationale: The correct answer is B: eukaryotic. Eukaryotic cells have a well-defined nucleus that encloses the genetic material. The nucleus is a distinguishing feature of eukaryotic cells, separating them from prokaryotic cells (choice A) which lack a nucleus. Anucleate cells (choice C) are cells that do not have a nucleus at all. Haploid cells (choice D) contain a single set of chromosomes, but this does not necessarily imply the presence of a nucleus. Therefore, the presence of a nucleus is what categorizes cells as eukaryotic.