Question

prions v. viroids → which statement is completely true? a. prions lack a capsid, viroids lack nucleic acid. b. viroids contain dna and rna, prions have only rna. c. prion particles can increase in numbers, viroids cannot. d. viroids require rna polymerase, prions do not. e. prions can recombine with host the genome, while viroids cannot. f. none of the above are completely true.

Explanation:

Prions are mis - folded proteins with no nucleic acid (DNA or RNA) and no capsid. Viroids are small, circular, single - stranded RNA molecules with no protein capsid. Prions do not require RNA polymerase for replication as they are proteins, and they do not combine with host genome. Viroids replicate using host - cell RNA polymerase and do not increase in number in the same way as prions.

Answer:

A. Prions lack a capsid, viroids lack nucleic acid. (This statement is incorrect as viroids are RNA molecules).
B. Viroids contain DNA and RNA, prions have only RNA. (Incorrect as viroids are RNA only and prions are proteins).
C. Prion particles can increase in numbers, viroids cannot. (Incorrect as viroids can replicate).
D. Viroids require RNA polymerase, prions do not. (Correct. Viroids use host - cell RNA polymerase for replication and prions are mis - folded proteins that induce mis - folding in normal proteins).
E. Prions can recombine with host the genome, while viroids cannot. (Incorrect as prions do not recombine with host genome).
F. None of the above are completely true. (Incorrect as option D is correct).
So the answer is D. Viroids require RNA polymerase, prions do not.