Which term describes an organism whose cells contain nuclei?

• A. Prokaryote
• B. Eukaryote
• C. Endospore
• D. Nitrogen fixation

Answer: (B)

Cells that house their DNA in a membrane-bound nucleus are eukaryotic. In these organisms, the genetic material is enclosed within a nucleus that is separated from the cytoplasm by a nuclear envelope, and the genome is organized into multiple linear chromosomes with associated proteins. This contrasts with prokaryotes, whose cells lack a true nucleus and store DNA in a nucleoid region inside the cytoplasm. Eukaryotes also typically contain other membrane-bound organelles, like mitochondria and the endoplasmic reticulum. The other terms refer to a survival structure produced by some bacteria or to a metabolic process carried out by certain microbes, not to the presence of a nucleus.