Given a scientific passage and an answer, generate a question for the given answer.

[EX Q]: Passage: When a fluorine atom gains an electron, it becomes a negative fluoride ion. Answer: fluoride ion
[EX A]: When a fluorine atom gains an electron, it becomes a negative what?

[EX Q]: Passage: Chlamydia is the most common bacterial STI in the U. S. Females are more likely to develop it than males. Symptoms may include burning during urination and a discharge from the vagina or penis. Answer: chlamydia
[EX A]: What is the most common bacterial sti in the u. s.?

[EX Q]: Passage: Prokaryotic cells are cells that lack a nucleus. The DNA in prokaryotic cells is in the cytoplasm, rather than enclosed within a nuclear membrane. All the organisms in the Bacteria and Archaea Domains have prokaryotic cells. No other organisms have this type of cell. Organisms with prokaryotic cells are called prokaryotes . They are all single-celled organisms. They were the first type of organisms to evolve. They are still the most numerous organisms today. Answer: a nucleus
[EX A]:
What significant part of the cell do prokaryotic cells lack?