outline key structural features of a prokaryotic cell as found in a typical bacterium, including: unicellular, generally 1–5 µm diameter, peptidoglycan cell walls, circular DNA, 70S ribosomes, absence of organelles surrounded by double membranes
Cambridge A-Level Biology – Cells as the Basic Units of Living Organisms
Cells as the Basic Units of Living Organisms
Key Structural Features of a Typical Prokaryotic Cell (Bacterium)
Prokaryotic cells are the simplest type of cells and are exemplified by bacteria. The main characteristics are listed below.
Unicellular organism – each bacterium is a single, independent cell.
Size: generally between \$1\ \mu\text{m}\$ and \$5\ \mu\text{m}\$ in diameter.
Cell wall composed of peptidoglycan, providing structural support and shape.
Genetic material: a single, circular DNA molecule located in the nucleoid region (no true nucleus).
Ribosomes: 70S ribosomes (30S small subunit + 50S large subunit) for protein synthesis.
Absence of membrane‑bound organelles such as mitochondria, chloroplasts, endoplasmic reticulum or Golgi apparatus.
Any internal structures (e.g., inclusion bodies, plasmids) are not surrounded by double membranes.
Summary Table
Feature
Description
Organism type
Unicellular bacterium
Typical diameter
\$1\text{–}5\ \mu\text{m}\$
Cell wall composition
Peptidoglycan (murein) layer
Genetic material
Circular DNA chromosome (plus possible plasmids)
Ribosomes
70S ribosomes (30S + 50S subunits)
Membrane‑bound organelles
Absent
Double‑membrane structures
None (except the plasma membrane)
Suggested diagram: Schematic cross‑section of a typical bacterium showing the peptidoglycan cell wall, plasma membrane, nucleoid region with circular DNA, 70S ribosomes, and absence of double‑membrane organelles.