Question
Prepare a detailed comparison between prokaryotic and eukaryotic cells covering at least 10 features. Give two examples of each. Which cell type is considered more primitive and why?
(NEET 2022, similar pattern)
Solution — Step by Step
Prokaryotic cell (Greek: pro = before, karyon = nucleus): Cells that lack a true membrane-bound nucleus. The genetic material lies in a region called the nucleoid without a nuclear membrane.
Eukaryotic cell (Greek: eu = true, karyon = nucleus): Cells with a well-defined nucleus enclosed by a nuclear membrane. They contain membrane-bound organelles.
| Feature | Prokaryotic | Eukaryotic |
|---|---|---|
| Nuclear membrane | Absent | Present |
| Genetic material | Circular DNA, no histones | Linear DNA wrapped around histones |
| Cell size | 0.1-5 μm | 10-100 μm |
| Membrane-bound organelles | Absent | Present (mitochondria, ER, Golgi, etc.) |
| Ribosomes | 70S (50S + 30S) | 80S (60S + 40S) in cytoplasm |
| Cell wall | Present (peptidoglycan in bacteria) | Present in plants/fungi (cellulose/chitin), absent in animals |
| Cell division | Binary fission | Mitosis / Meiosis |
| Plasmids | Often present | Rare (found in yeast) |
| Cytoskeleton | Absent or primitive | Well-developed |
| Transcription & translation | Coupled (occur together) | Separate (transcription in nucleus, translation in cytoplasm) |
| Examples | E. coli, Staphylococcus, cyanobacteria | Plant cells, animal cells, fungi, protists |
Prokaryotic cells appeared first in Earth’s history — fossil evidence of bacteria dates to 3.5 billion years ago, while the earliest eukaryotic fossils are about 1.5-2 billion years old.
Prokaryotes are structurally simpler: no nuclear membrane, no compartmentalised organelles, smaller genome. The endosymbiotic theory (Lynn Margulis, 1967) proposes that eukaryotic cells evolved when ancestral prokaryotes engulfed other prokaryotes — the engulfed bacteria eventually became mitochondria (aerobic bacteria) and chloroplasts (cyanobacteria).
Why This Works
The fundamental distinction is compartmentalisation. Eukaryotic cells have internal membrane-bound compartments that allow different biochemical reactions to occur simultaneously in different locations. Prokaryotes do everything in one compartment (the cytoplasm).
This compartmentalisation gives eukaryotes advantages: they can be larger (internal transport systems), perform complex functions (organelle specialisation), and carry more genetic information (nuclear membrane protects DNA and allows RNA processing before translation).
However, prokaryotes are not “inferior” — they’re incredibly successful. They outnumber eukaryotic cells on Earth by a massive margin and thrive in extreme environments where eukaryotes cannot survive.
Alternative Method
For quick revision, remember the “3 Ns” that prokaryotes lack: Nuclear membrane, Nucleus (true), Nucleolus. They also lack the “3 Ms”: Mitochondria, Membrane-bound organelles, Meiosis.
NEET MCQs on this topic often test specific features. Common traps: “Prokaryotes lack ribosomes” — FALSE, they have 70S ribosomes. “All prokaryotes lack cell wall” — FALSE, most bacteria have peptidoglycan cell walls (exception: Mycoplasma). “All eukaryotes have mitochondria” — nearly true, but some anaerobic protists (like Giardia) have reduced versions called mitosomes.
Common Mistake
Students often write that prokaryotes have “no DNA.” This is completely wrong — prokaryotes have DNA, it’s just not enclosed in a nuclear membrane. Their DNA is typically a single circular chromosome in the nucleoid region, often supplemented by small circular plasmids. The absence of a nuclear membrane does NOT mean absence of genetic material.