Question
Give a detailed comparison between prokaryotic and eukaryotic cells. Include at least 8 points of difference in a table format.
Solution — Step by Step
The words come from Greek: pro = before, eu = true, karyon = nucleus.
Prokaryotes are organisms whose cells lack a membrane-bound nucleus — the genetic material (DNA) floats freely in the cytoplasm in a region called the nucleoid.
Eukaryotes have a well-defined nucleus enclosed by a double membrane (nuclear envelope). They are structurally far more complex.
This is not just a trivial anatomical difference — it reflects 1.5 billion years of evolutionary divergence. Prokaryotes were the first life forms; eukaryotes evolved from them.
| Feature | Prokaryotes | Eukaryotes |
|---|---|---|
| Nucleus | No membrane-bound nucleus; nucleoid region | Well-defined nucleus with nuclear envelope |
| Size | Smaller: 1–10 μm | Larger: 10–100 μm |
| Membrane-bound organelles | Absent (no mitochondria, ER, Golgi) | Present (mitochondria, ER, Golgi, etc.) |
| Ribosomes | 70S (50S + 30S subunits) | 80S (60S + 40S subunits) in cytoplasm |
| DNA structure | Single circular chromosome; no histones | Multiple linear chromosomes; associated with histone proteins |
| Cell wall | Present in bacteria (peptidoglycan) | Present in plants (cellulose), fungi (chitin); absent in animals |
| Cell division | Binary fission | Mitosis and meiosis |
| Flagella | Simple structure (flagellin protein) | Complex structure (9+2 arrangement of microtubules) |
| Plasmids | Common (extra circular DNA) | Rare (found in some yeast) |
| Examples | Bacteria, Archaea | Plants, animals, fungi, protists |
Why ribosome size matters: Prokaryotes have 70S ribosomes; eukaryotes have 80S. This is clinically vital — many antibiotics (like streptomycin, tetracycline, erythromycin) specifically target 70S ribosomes, killing bacteria without harming our 80S ribosomes. This selectivity is why these drugs are relatively safe for human use.
Why no membrane-bound organelles in prokaryotes matters: Eukaryotes achieve metabolic compartmentalisation — different reactions happen in different organelles (oxidative phosphorylation in mitochondria, protein synthesis in ribosomes, lipid synthesis in ER). Prokaryotes perform all these at the plasma membrane or in the cytoplasm.
Endosymbiotic theory: Mitochondria and chloroplasts in eukaryotes are thought to have evolved from prokaryotic ancestors that were engulfed but not digested. Evidence: they have their own 70S ribosomes, circular DNA, and divide by binary fission — just like bacteria.
Why This Works
This question is “medium” because a surface-level answer (2–3 differences) scores low marks. A high-scoring answer connects each difference to a functional consequence (antibiotic action, organelle evolution, cell division) — that’s what this solution demonstrates.
The ribosome difference is particularly important for NEET because it bridges biology and medicine (antibiotics).
Alternative Method
For Class 11 exams, a mnemonic for remembering prokaryote features: “No MEGO” — No Membrane-bound organelles, no Endoplasmic reticulum, no Golgi apparatus, no (true) nucleus, no Organised histones (they have HU proteins instead, but not true histones).
Common Mistake
Students often write “prokaryotes have no cell wall.” This is incorrect — most prokaryotes (bacteria) DO have a cell wall, made of peptidoglycan (murein). What they LACK is a membrane-bound nucleus and membrane-bound organelles. The cell wall question is about composition and structure, not presence or absence.
NEET frequently asks: “Which of the following is common to both prokaryotes and eukaryotes?” The answer is usually ribosomes (though the type differs). Both have ribosomes because both need to synthesise proteins. Also, both have DNA as genetic material and both have a cell membrane.