The correct answer is a) a nuclear membrane.
All eukaryotic cells are defined by the presence of a nucleus, which is encased in a nuclear membrane. This structure separates the genetic material from the cytoplasm, allowing for more complex regulation of gene expression and cellular processes. In contrast, prokaryotes, which include bacteria and archaea, do not have a nucleus or a nuclear membrane; instead, their DNA is located in a region called the nucleoid.
The options b) a nucleoid, c) few to no organelles in the cytoplasm, d) a cell wall, and e) few to no proteins associated with the DNA do not apply to all eukaryotes:
- b) a nucleoid: This is characteristic of prokaryotes, not eukaryotes.
- c) few to no organelles in the cytoplasm: Eukaryotes typically have a variety of organelles, such as mitochondria, endoplasmic reticulum, and Golgi apparatus.
- d) a cell wall: While some eukaryotes (like plants and fungi) have a cell wall, animal cells do not.
- e) few to no proteins associated with the DNA: Eukaryotic DNA is heavily associated with proteins known as histones, which help package DNA into a compact form.
Therefore, among the options provided, the presence of a nuclear membrane is the defining characteristic of all eukaryotic cells.