Identify which statements are correct.

Correct Answer: D

Rationale: The correct answer is D because protozoans do not have cell walls. They are single-celled organisms that lack a rigid cell wall. This distinguishes them from other microorganisms like bacteria, fungi, and algae which have distinct cell wall compositions such as peptidoglycan, chitin, and cellulose respectively. Choice A is incorrect as not all bacteria have peptidoglycan in their cell walls, some have other types of cell wall structures. Choice B is incorrect as not all fungi have chitin in their cell walls, some may have different components. Choice C is incorrect as not all algae have cellulose in their cell walls, there are variations in cell wall composition among different algal species.

Correct Answer: C

Rationale: The correct match for the terms is: 1 - D 2 - C 3 - B 4 - E 5 - A 6 - F Rationale: 1. Term 1 corresponds to definition D, as per choice C. 2. Term 2 matches with definition C, as per choice C. 3. Term 3 aligns with definition B, as per choice C. 4. Term 4 correlates with definition E, as per choice C. 5. Term 5 matches with definition A, as per choice C. 6. Term 6 corresponds to definition F, as per choice C. Summary: - Choice A has incorrect matches for terms 1, 2, 3, 5, and 6. - Choice B has incorrect matches for terms 1, 2, 3, and 4. - Choice D has incorrect matches for terms 1, 2, 4, and 6. Therefore, the correct answer

Correct Answer: D

Rationale: The correct answer is D, peptidoglycan. Peptidoglycan is a component of bacterial cell walls that can trigger fever in humans. It is a sturdy molecule that can withstand autoclaving. A: Endotoxin is a component of the outer membrane of Gram-negative bacteria, not resistant to autoclaving. B: Lipid A is the toxic component of endotoxin, not resistant to autoclaving. C: Lipopolysaccharide is the major component of the outer membrane of Gram-negative bacteria, not resistant to autoclaving.

Correct Answer: A

Rationale: The correct answer is A. A second exposure to an allergen does not lead to the development of autoimmune disorders. The key mechanisms involved in autoimmune disorders are self-tolerance breakdown and immune system attacking self-antigens. Explanation: 1. B: Cross-reaction of antibodies formed against foreign antigens with self-antigens is a possible mechanism for autoimmune disorders. 2. C: Exposure of previously 'hidden' self-antigens to the adaptive immune system can trigger autoimmune responses. 3. D: Mutation followed by the appearance of membrane proteins not previously present can lead to autoimmune disorders, as the immune system may recognize these proteins as foreign. Summary: Choice A is incorrect because a second exposure to an allergen does not cause the immune system to target self-antigens, which is the hallmark of autoimmune disorders. Choices B, C, and D are more plausible mechanisms for the development of autoimmune disorders.

Correct Answer: A

Rationale: Terminal deoxynucleotidyl transferase (TdT) adds nucleotides to the 3' end of DNA fragments in a template-independent manner. This results in the production of fragments with poly A or poly C tails. TdT does not add poly T tails, making option D incorrect. It also does not specifically add only poly C tails (option B) or poly A tails (option C). The addition of poly A or poly C tails by TdT is essential for techniques like DNA sequencing and PCR, where these tails are utilized for downstream applications.