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A2.2.5—Prokaryote cell structure

Prokaryotic cells organize metabolism and heredity without a nucleus, using a membrane-bounded cytoplasm containing 70S ribosomes, circular DNA, and specialized surface structures.

Syllabus
First assessment 2025
Objective
A2.2.5
Level
HL

Exam analysis

Chance of appearing10%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper1
Typical marks1–2

Common command terms

  • Identify
  • Compare
  • Label
  • Outline
  • State
  • Draw
  • Distinguish
  • Annotate

Scoring notes

Common mistake
Assigning a nucleus or membrane-bound organelles to a prokaryotic cell.

Recent exam appearances

May 2025Paper1B ["HL"] · TZ12(b)[ 1 ]A2.2.5—Prokaryote cell structure
May 2024Paper2 ["HL"] · TZ28(a)[ 4 ]A2.2.5—Prokaryote cell structure
May 2023Paper1 ["HL"] · TZ12[ 1 ]A2.2.5—Prokaryote cell structure
May 2022Paper2 ["HL"] · TZ22(b)(i)[ 2 ]A2.2.5—Prokaryote cell structure
May 2019Paper2 ["HL"] · TZ13(a)[ 4 ]A2.2.5—Prokaryote cell structure
Practice this objective

Coverage 2012–2025 · Updated 15 Jul 2026

Recognize the Required Gram-Positive Prokaryote Model

A typical Gram-positive eubacterium such as Bacillus or Staphylococcus has a cell wall outside a plasma membrane, cytoplasm with 70S ribosomes, and naked circular DNA in a nucleoid region.

Structure Recognition or role
Cell wall Rigid outer layer supporting cell shape
Plasma membrane Selective exchange and membrane-based processes
Cytoplasm Aqueous reaction space
70S ribosomes Protein synthesis
Naked DNA loop Main chromosome without a nuclear envelope
Plasmid, when present Small additional circular DNA molecule

A micrograph showing a small walled cell with dispersed ribosomes and no nucleus is consistent with a prokaryote; its DNA occupies a nucleoid rather than a membrane-bound nucleus.

Prokaryotic structure varies, but detailed exceptions such as wall-less bacteria are outside this objective. No nucleus does not mean no DNA.

Prokaryote cell structure

Assessment in practice

1–3 marks
How it is assessed

This objective is assessed through structured response, commonly using Identify / Compare / Label.

Command terms

Identify / Compare / Label / Outline / State / Draw / Distinguish / Annotate

What earns marks

Build the answer around this relationship: Prokaryotic DNA occupies a nucleoid rather than a membrane-bounded nucleus.

Watch for

Assigning a nucleus or membrane-bound organelles to a prokaryotic cell.

Representative question

Question 1

[Maximum number: 9]

Escherichia coli is a unicellular organism, so each cell must carry out all of the processes required for life. Outline the functions of each of the structures in the cells of Escherichia coli.

SL Retrieval: Read, Identify, Draw

The SL core is a practical chain. First, understand cells as structural and functional units. Then use microscopes correctly: prepare, stain, calibrate, measure, and choose a method based on resolution and the detail needed. Finally, identify cell types from visible evidence and draw only what the micrograph shows. This is how the topic turns from definitions into exam performance.

  • Cell theory: cells are structural and functional units.
  • Microscopy: resolution, calibration, magnification, actual size, and scale bars.
  • Cell identity: universal parts, prokaryote/eukaryote differences, and plant/animal/fungal evidence.
  • Micrograph work: justify from visible structures, scale, and context.
  • Drawing: clear lines, no shading, visible labels only, scale/magnification included.

Concept essentials

  • Prokaryotic DNA occupies a nucleoid rather than a membrane-bounded nucleus.
  • Bacterial cytoplasm contains 70S ribosomes.
  • The main chromosome is commonly circular and plasmids may carry additional genes.
  • A peptidoglycan wall supports and protects most bacterial cells.