Cell classification — The single best criterion to distinguish a prokaryotic cell from a eukaryotic cell

Introduction:
The most fundamental distinction in cellular organization is between prokaryotes and eukaryotes. This question asks for the simplest, most reliable feature to tell them apart quickly and correctly in general biology contexts.

Given Data / Assumptions:

• Unknown cell type under consideration.
• Basic microscopy or structural information available.
• Goal: use a single criterion that is broadly applicable.

Concept / Approach:
Prokaryotic cells lack a membrane-bound nucleus; their DNA resides in a nucleoid region. Eukaryotic cells have a true nucleus enclosed by a nuclear envelope and also possess other membrane-bound organelles (Golgi, ER, mitochondria, etc.).

Step-by-Step Solution:

Verification / Alternative check:
The presence of other membrane-bound organelles (e.g., Golgi bodies, mitochondria) also implies eukaryote, but the nucleus is the simplest and most universal single indicator.

Why Other Options Are Wrong:

• Plasma membrane: common to all cells.
• Presence of DNA: universal, not discriminative.
• Entire organism vs part: many counterexamples render it unreliable.
• Membrane-bound organelles: correct implication but less minimal than the nucleus check; the question asks for the simplest way.

Common Pitfalls:
Confusing a dense nucleoid with a true nucleus; only eukaryotes have a nucleus bounded by a double membrane with nuclear pores.

Final Answer:
see if a nucleus is present.