Prokaryotes Have DNA in Cytoplasm, Not Nucleus

Steps:

• Define prokaryote: unicellular organism lacking a membrane-bound nucleus.
• Note key trait: genetic material (DNA) exists as nucleoid in cytoplasm.
• Contrast with eukaryote: DNA enclosed in nucleus.
• Identify feature: cytoplasmic DNA distinguishes prokaryotes.

Why A is correct:

• Prokaryotes contain a single circular DNA molecule free in the cytoplasm, per the biological definition of lacking nuclear membrane.

Why the others are wrong:

• B: Cell walls occur in many prokaryotes and some eukaryotes (e.g., plants, fungi).
• C: Nucleus is exclusive to eukaryotes, identifying them instead.
• D: Ribosomes are present in both prokaryotes and eukaryotes for protein synthesis.

Final answer: A