Bacteria as Prokaryotic Unicellular Organisms

Steps:

• Recall that bacteria belong to the domain Bacteria, characterized by prokaryotic cells lacking a nucleus.
• Eliminate options based on prokaryotic traits: no nucleus rules out A.
• Check for universal features: all bacteria are unicellular, unlike multicellular fungi or parasites.
• Confirm D matches the definition of bacteria as single-celled prokaryotes.

Why D is correct:

• By definition, bacteria are prokaryotic organisms that exist as single-celled (unicellular) entities, without complex multicellular structures.

Why the others are wrong:

• A: Bacteria are prokaryotes and lack a true nucleus; they have nucleoids instead.
• B: Not all bacteria are parasites; many are free-living in environments like soil or water.
• C: Hyphae are thread-like structures in fungi, not bacteria.

Final answer: D