The main difference between a prokaryotic cell and a eukaryotic cell is the absence of?

JODHPUR AIIMS SNO-2018

Applied Microbiology & Infection control

Easy

Appeared in: JODHPUR AIIMS SNO-2018

Explanation

The defining and primary difference between prokaryotic and eukaryotic cells is the absence of a true, membrane-bound nucleus in prokaryotes.
In prokaryotic cells, the genetic material is concentrated in a region of the cytoplasm called the nucleoid, which lacks a surrounding membrane.
In contrast, eukaryotic cells have a well-defined nucleus that houses the cell's genetic material, separating it from the cytoplasm.

Option A: The plasma membrane is a universal feature found in both prokaryotic and eukaryotic cells, where it functions as a selective barrier.
Option B: While it is true that prokaryotes lack mitochondria, this is considered a secondary difference. The absence of a nucleus is the most fundamental and defining characteristic.
Option D: Flagella are not a universal feature of all cells, but they can be found in both prokaryotic and eukaryotic cells for motility. Therefore, their absence is not a defining difference.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Structural differences between prokaryotic and eukaryotic cells as background academic context rather than a clinical decision trigger.
The structural differences between prokaryotic (bacterial) and eukaryotic (human) cells are the foundation of antimicrobial therapy. Antibiotics are designed to target specific prokaryotic structures, like the cell wall or ribosomes, that are absent or different in human cells.
For example, penicillin targets the synthesis of the peptidoglycan cell wall, a structure unique to bacteria. This allows the drug to kill bacteria without harming the patient's own eukaryotic cells.
What if a bacterium developed a mutation that encased it in a structure similar to a eukaryotic membrane? This could potentially make it resistant to certain antibiotics that target the outer bacterial structures, posing a significant clinical challenge.

How to Approach the Question

First, understand the question's core: it asks for the 'main' difference, implying the most fundamental or defining characteristic that separates prokaryotes from eukaryotes.
Recall the basic definitions of prokaryotic and eukaryotic cells. The prefix 'pro-' means 'before' and 'karyon' means 'nucleus', so prokaryote means 'before nucleus'. The prefix 'eu-' means 'true', so eukaryote means 'true nucleus'.
Evaluate each option based on this core definition.
Option A (Plasma membrane): Recall that all cells are enclosed by a plasma membrane. This is a similarity, not a difference.
Option B (Mitochondria): Recall that mitochondria are membrane-bound organelles. Prokaryotes lack these, but is this the main difference?
Option C (True nucleus): This directly relates to the etymology and the primary classification criterion. The lack of a membrane-bound nucleus is the hallmark of a prokaryote.

Concept Tested & Keywords

Concept Tested: Structural differences between prokaryotic and eukaryotic cells.
Stem keywords: prokaryotic cell, eukaryotic cell, main difference, absence
Lead-in keywords: absence of

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E6 Microbiology Essentials Sastry 4e Part 1 p. 37-39