Biology ยท WBI12 (Unit 2)

Eukaryotic and prokaryotic cells

All organisms are made of cells, but the cells of bacteria are built very differently from those of plants and animals.

Eukaryotic cells

Animal and plant cells are eukaryotic: their DNA is in a nucleus, and they have membrane-bound organelles such as mitochondria, the endoplasmic reticulum and the Golgi apparatus. Their ribosomes are 80S.

Prokaryotic cells

Bacteria are prokaryotic: no nucleus (DNA is a circular chromosome in the cytoplasm), no membrane-bound organelles, smaller 70S ribosomes. They have a cell wall (made of peptidoglycan, not cellulose); many also have plasmids, and some have flagella and a capsule.

Plant extras

Plant cells also have a cellulose cell wall, chloroplasts, a large permanent vacuole, and plasmodesmata connecting neighbouring cells.

Worked example

A cell has 70S ribosomes, a circular chromosome and no nucleus. What type of cell is it?

  1. No nucleus and 70S ribosomes are features of prokaryotes.

Answer: A prokaryotic cell (a bacterium).

Key idea: Eukaryotic: nucleus, membrane-bound organelles, 80S ribosomes. Prokaryotic: no nucleus, circular DNA, plasmids, 70S ribosomes.

Check yourself

  1. Which structure is found in prokaryotic cells but not in animal cells?
    • Nucleus
    • Plasmid
    • Mitochondrion
    • Golgi apparatus
    Show answer

    Plasmid. Plasmids are small extra loops of DNA found in many bacteria.

  2. What size are the ribosomes in a bacterium?
    • 80S
    • 60S
    • 90S
    • 70S
    Show answer

    70S. Prokaryotes have 70S ribosomes; eukaryotic cytoplasm has 80S.

  3. Which is found in plant cells but not animal cells?
    • Ribosomes
    • Cellulose cell wall
    • Cell surface membrane
    • Mitochondria
    Show answer

    Cellulose cell wall. Plant cells have a cellulose cell wall.

  4. Which of these is a eukaryotic cell?
    • Escherichia coli
    • A cyanobacterium
    • A leaf palisade cell
    • Staphylococcus aureus
    Show answer

    A leaf palisade cell. Plant cells are eukaryotic; the others are bacteria.

  5. How is DNA usually arranged in a prokaryotic cell?
    • A circular chromosome free in the cytoplasm
    • Linear chromosomes in a nucleus
    • Inside mitochondria only
    • Bound to the cell wall
    Show answer

    A circular chromosome free in the cytoplasm. Prokaryotes have no nucleus; their main DNA is one circular chromosome.

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Last updated 7 November 2026. Spotted a mistake? Email alevel@lifereadysociety.com.