Helicobacter cells are classified as prokaryotes primarily because they lack a nucleus with nucleic acids inside. Prokaryotes, such as bacteria including Helicobacter, do not have a membrane-bound nucleus, and their genetic material is typically found in a nucleoid region rather than within a true nucleus as seen in eukaryotic cells.
The other options provided are characteristics but not defining criteria for prokaryotes:
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Move using flagella: While many prokaryotes, including Helicobacter, move using flagella, this is not a defining characteristic of prokaryotes.
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Have ribosomes that function to make proteins: Both prokaryotes and eukaryotes have ribosomes for protein synthesis, so this is not a distinguishing feature.
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Lack a cell membrane composed of phospholipids: Prokaryotes do possess cell membranes, and these membranes are typically composed of phospholipids.
Thus, the correct response is related to the lack of a membrane-bound nucleus.