Physical methods of microbial control will typically sterilize, whereas chemical methods will only disinfect.

A. does not have thymine: DNA contains the nitrogenous base thymine, whereas RNA lacks thymine. Instead, RNA uses uracil in place of thymine during base pairing. Because thymine is absent from RNA molecules, this difference is one of the key biochemical distinctions between RNA and DNA structure.

B. has uracil: RNA contains the nitrogenous base uracil, which pairs with adenine during RNA synthesis and function. In DNA, thymine performs this role instead. The substitution of uracil for thymine is a defining molecular feature that distinguishes RNA nucleotides from DNA nucleotides.

C. All of the choices are correct: Each of the listed statements accurately describes a property unique to RNA compared with DNA. RNA lacks thymine, contains uracil, typically exists as a single-stranded molecule, and contains ribose sugar rather than deoxyribose. Because every option describes a valid structural difference, this is the most accurate answer.

D. is typically one strand of nucleotides (single stranded): RNA molecules are generally single-stranded, allowing them to fold into complex secondary and tertiary structures that support functions such as translation and gene regulation. DNA, in contrast, usually exists as a double-stranded helix with complementary base pairing between strands.

E. has ribose: RNA nucleotides contain ribose sugar, which includes a hydroxyl group on the 2′ carbon of the pentose ring. DNA contains deoxyribose, which lacks this oxygen atom. This chemical difference contributes to RNA being more reactive and less stable than DNA.

A. Endotoxin: Endotoxins are lipopolysaccharide (LPS) components of the outer membrane of Gram-negative bacteria. When these bacteria die, LPS is released into the host’s bloodstream, triggering a strong immune response. The lipid A portion of endotoxin activates macrophages to release cytokines such as interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-α), which act on the hypothalamus to induce fever.

B. Exotoxin: Exotoxins are proteins secreted by both Gram-positive and Gram-negative bacteria during their growth. They are highly potent and can cause tissue damage and specific clinical syndromes, but they are not primarily responsible for fever following bacterial death.

C. Capsule proteins: Capsule components contribute to bacterial virulence by preventing phagocytosis and promoting adherence. While they enhance bacterial survival, capsule proteins do not directly trigger the cytokine-mediated fever response that is associated with endotoxin release.