Bacterial Cell Structure: Prokaryotic vs Eukaryotic
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Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
Key concept
Bacterial cells are prokaryotic: they lack a membrane-bound nucleus. DNA exists as a single circular chromosome in the cytoplasm, often with additional small loops of DNA called plasmids. They have no mitochondria, no endoplasmic reticulum and no chloroplasts.
Understanding how bacterial cells differ from eukaryotic cells (animal and plant) is essential for classification and disease topics. The prokaryotic cell structure appears in Paper 2, Paper 4 and Paper 6 questions. This guide covers all the structural features required by the syllabus.
Key Features of Bacterial Cells
No membrane-bound nucleus: the DNA is a single, circular chromosome located in a region called the nucleoid.
Plasmids: small circular loops of extra DNA that can be transferred between bacteria. Plasmids often carry genes for antibiotic resistance.
Cell wall: made of peptidoglycan (not cellulose or chitin). Gives the cell its shape.
Cell membrane: just inside the cell wall, controlling entry and exit of substances.
Cytoplasm: contains 70S ribosomes (smaller than the 80S ribosomes in eukaryotic cells).
Flagellum (plural: flagella): a whip-like tail used for movement. Not all bacteria have flagella.
Slime capsule: a sticky outer layer that protects the bacterium from the host immune system and from drying out.
Prokaryotic vs Eukaryotic Cells
Feature
Prokaryotic (bacteria)
Eukaryotic (animal / plant)
Nucleus
No membrane-bound nucleus
Membrane-bound nucleus present
DNA
Circular chromosome + plasmids
Linear chromosomes in nucleus
Mitochondria
Absent
Present
Ribosomes
Smaller (70S)
Larger (80S)
Cell wall
Peptidoglycan
Cellulose (plants) / absent (animals)
Size
1–5 μm
10–100 μm
Endoplasmic reticulum
Absent
Present
Bacterial Size and Observation
Bacteria are typically 1–5 μm in length: about 10 times smaller than a typical animal cell. They can be seen under a light microscope at high magnification (×400 or higher) but individual structures like flagella require an electron microscope.
Common bacterial shapes:
Cocci: spherical (e.g. Staphylococcus)
Bacilli: rod-shaped (e.g. E. Coli, Lactobacillus)
Spirilla: spiral-shaped
Lactobacillus is named in the syllabus: it is a rod-shaped bacterium used in yoghurt production. It ferments lactose (milk sugar) into lactic acid.
Try a focused question (3 marks)
State three differences between a bacterial cell and a plant cell. (3 marks)
Show the answer and marking guidance
Bacterial cells have no membrane-bound nucleus; plant cells have a nucleus with a nuclear envelope.
Bacterial cell walls are made of peptidoglycan; plant cell walls are made of cellulose.
Bacterial cells have no mitochondria or chloroplasts; plant cells have both (chloroplasts in green cells).
Original Cambridge-style practice written for this site. It is not an official Cambridge past-paper question.
Common mix-ups to avoid
Check these points against your own answer before moving on.
Saying bacteria have no DNA: they do, it is just not enclosed in a nucleus.
Confusing plasmids with chromosomes: plasmids are extra, smaller loops of DNA separate from the main chromosome.
Saying bacterial cell walls are made of cellulose: they are made of peptidoglycan.