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NDA Biology · Cell Biology

Prokaryotic vs Eukaryotic Cells

Prokaryotic cells (bacteria) have no membrane-bound nucleus — just a 'nucleoid' of naked circular DNA — and no membrane-bound organelles; eukaryotic cells (plants, animals, fungi) have a true nucleus and organelles like mitochondria.

All Cell Biology notesNDA Biology strategy

Why this matters

A tight, high-frequency 5-PYQ cluster, all single-fact recall. The bank tests the same handful of points: prokaryotes lack a true nucleus (they have a nucleoid), lack membrane-bound organelles (no mitochondria), have a single circular chromosome, and their DNA is 'naked' (no histone proteins). All EASY or MODERATE.

Concept 1 of 2

Prokaryote vs eukaryote — the contrast table

Intuition

The whole subtopic rests on one comparison. A eukaryote has a membrane-bound nucleus and organelles; a prokaryote has neither — its DNA sits free as a nucleoid and it has no mitochondria. Anything 'membrane-bound' is the eukaryote's signature.

Definition

The key differences between the two cell types:

  • Nucleus — eukaryotes have a true membrane-bound nucleus; prokaryotes have only a nucleoid (no membrane).
  • Organelles — eukaryotes have membrane-bound organelles (mitochondria, ER, Golgi); prokaryotes have none.
  • Both have a cell wall, plasma membrane and ribosomes — so these do NOT distinguish them.
  • 'Exclusively present in a eukaryote' = the mitochondrion (a membrane-bound organelle).
  • 'NOT present in a prokaryote' = the nucleus (and other membrane-bound organelles).
ProkaryoteNucleoidnaked, circular DNANo nucleus, no organellesEukaryoteNucleusmitochondrionMembrane-bound nucleus + organelles

Both have a wall, membrane and ribosomes. Only the eukaryote has a true nucleus and membrane-bound organelles.

FeatureProkaryoteEukaryote
NucleusNucleoid (no membrane)True membrane-bound nucleus
'Not present in a prokaryote' → the nucleus.
MitochondriaAbsentPresent
'Exclusively in eukaryotes' → mitochondria (membrane-bound).
Cell wallPresentPresent (plants/fungi)
Plasma membranePresentPresent
RibosomesPresent (70S)Present (80S)
Cell wall, plasma membrane and ribosomes are in BOTH — so they can never be the answer to 'what's exclusive / what's missing'. Look for the membrane-bound feature.
Practice this conceptself-check · 4 quick reps

Try it yourself

Which organelle is found ONLY in eukaryotic cells: cell wall, plasma membrane, nucleic acid, or mitochondria?

Practice — Level 1 (4 reps)

Quick reps to lock in the method. Try each, then check.

  1. 1.
    Which organelle is NOT found in prokaryotic cells?
  2. 2.
    Which structure is exclusively present in eukaryotic cells?
  3. 3.
    Do prokaryotes have a membrane-bound nucleus?
  4. 4.
    Name three structures present in BOTH cell types.

From the bank · past-year question

Example 1Cell BiologyEASY
Which one of the following structures is not present in a prokaryotic cell?

[Q69 · Apr · 2023]

Cell wall is NOT eukaryote-exclusive

Bacteria (prokaryotes) have a cell wall, so 'cell wall' can never be the answer to 'what is exclusive to eukaryotes'. The eukaryote-only answer is a membrane-bound structure — the nucleus or mitochondria.
Drill 2 more on prokaryote vs eukaryote — the contrast table

Concept 2 of 2

The nucleoid and 'naked' bacterial DNA

Intuition

Because a prokaryote has no nuclear membrane, its DNA floats free in a region called the nucleoid. That DNA is also called 'naked' — it isn't wrapped around histone proteins the way eukaryotic DNA is. And there's just one of it: a single circular chromosome.

Definition

Prokaryotic DNA facts:

  • The membrane-less region holding the DNA is the nucleoid (not nucleolus, not nucleosome).
  • Bacterial DNA is called 'naked' because it is NOT associated with histone proteins (eukaryotic DNA is wound around histones).
  • Most prokaryotes have a single circular chromosome — chromosome number = 1 (plus optional plasmids).
TermMeaning
NucleoidThe membrane-less DNA region of a prokaryote
Nucleoid — not nucleolus (eukaryotic) or nucleosome (DNA+histone unit).
'Naked' DNABacterial DNA NOT bound to histone proteins
'Naked because not associated with' → proteins (histones).
Chromosome numberUsually 1 (a single circular chromosome)
Practice this conceptself-check · 3 quick reps

Try it yourself

Bacterial DNA is described as 'naked'. What is it NOT associated with?

Practice — Level 1 (3 reps)

Quick reps to lock in the method. Try each, then check.

  1. 1.
    What is the membrane-less nuclear region of a prokaryote called?
  2. 2.
    Bacterial DNA is 'naked' because it lacks association with ___.
  3. 3.
    How many chromosomes does a typical prokaryote have?

From the bank · past-year question

Example 2Cell BiologyEASY
Bacterial DNA is referred to as naked because it is not\textbf{\text{not}} associated with :

[Q122 · Apr · 2024]

Nucleoid vs nucleolus vs nucleosome

The prokaryotic DNA region is the NUCLEOID. The nucleolus (makes ribosomes) and the nucleosome (DNA wound on histones) are EUKARYOTIC structures — both are distractors here.
Drill 1 more on the nucleoid and 'naked' bacterial dna

Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Reference tables (2)

Prokaryote vs eukaryote — the contrast table5 rows
FeatureProkaryoteEukaryote
NucleusNucleoid (no membrane)True membrane-bound nucleus
'Not present in a prokaryote' → the nucleus.
MitochondriaAbsentPresent
'Exclusively in eukaryotes' → mitochondria (membrane-bound).
Cell wallPresentPresent (plants/fungi)
Plasma membranePresentPresent
RibosomesPresent (70S)Present (80S)
Cell wall, plasma membrane and ribosomes are in BOTH — so they can never be the answer to 'what's exclusive / what's missing'. Look for the membrane-bound feature.
The nucleoid and 'naked' bacterial DNA3 rows
TermMeaning
NucleoidThe membrane-less DNA region of a prokaryote
Nucleoid — not nucleolus (eukaryotic) or nucleosome (DNA+histone unit).
'Naked' DNABacterial DNA NOT bound to histone proteins
'Naked because not associated with' → proteins (histones).
Chromosome numberUsually 1 (a single circular chromosome)

Watch out for (2)

Mastery check — 3 interleaved questions

Try each one before clicking. Questions are interleaved across the concepts above, not grouped — interleaving sharpens transfer.

Example 1Cell BiologyEASY
Eukaryotic cells are much more complex as compared to prokaryotes. Which one of the following structures is exclusively present in a eukaryotic cell?

[Q67 · Sep · 2023]

Example 2Cell BiologyEASY
In most prokaryotes, the chromosome number is :

[Q121 · Apr · 2024]

Example 3Cell BiologyEASY
Which one of the following is an organelle that is NOT found in prokaryotic cells?

[Q70 · Apr · 2018]

Drill every past-year question on this subtopic

5 questions from the bank — paginated, with cart and Word-export support.

Drill the 5 questions