Which is a prokaryote?
**Core Concept**
Prokaryotes are a group of organisms that lack a true nucleus and other membrane-bound organelles. They are characterized by their simple cell structure, which is typically smaller and more primitive than that of eukaryotes. Prokaryotes include bacteria and archaea.
**Why the Correct Answer is Right**
The correct answer is likely a bacterium, such as *Escherichia coli* or *Staphylococcus aureus*. Bacteria are prokaryotes that lack a true nucleus and other membrane-bound organelles. They have a single circular chromosome and a cell wall that provides structural support. The lack of a nucleus and other organelles makes it difficult for bacteria to perform complex cellular functions, such as protein synthesis and DNA replication.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because archaea are also prokaryotes, but they are a distinct group from bacteria. Archaea have a unique cell membrane and metabolic pathways that distinguish them from bacteria.
**Option B:** This option is incorrect because eukaryotes are a group of organisms that have a true nucleus and other membrane-bound organelles. Eukaryotes include plants, animals, fungi, and protists.
**Option C:** This option is incorrect because viruses are not considered living cells and do not fit into the prokaryote or eukaryote categories. Viruses require a host cell to replicate and carry out their life cycle.
**Clinical Pearl / High-Yield Fact**
One key difference between prokaryotes and eukaryotes is the presence of a true nucleus. Prokaryotes lack a nucleus and other membrane-bound organelles, making them more susceptible to environmental stressors and less able to perform complex cellular functions.
**Correct Answer: C. Virus**