Prokaryotic Organisms (Edexcel GCSE Biology: Combined Science)

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Prokaryotes

  • All living organisms can be grouped or ‘classified’ using a classification system that consists of five kingdoms. These five kingdoms are:
    • Animals
    • Plants
    • Fungi
    • Protoctists
    • Prokaryotes

  • The prokaryotes are different from the other four kingdoms (which are all eukaryotes) as prokaryotic organisms are always single-celled and do not contain a nucleus
  • Instead, the nuclear material of prokaryotic cells is found in the cytoplasm
  • Prokaryotic cells are also much smaller (about x1000 smaller) than eukaryotic cells
  • They are too small to contain chloroplasts or mitochondria
  • Bacteria are prokaryotic organisms

Bacteria

  • Bacteria, which have a wide variety of shapes and sizes, all share the following biological characteristics:
    • They are microscopic single-celled organisms
    • Possess a cell wall (made of peptidoglycan, not cellulose), cell membrane, cytoplasm and ribosomes
    • Lack a nucleus but contain a circular chromosome of DNA that floats in the cytoplasm
    • Plasmids are present in prokaryotes - these are small rings of DNA (also floating in the cytoplasm) that contain extra genes to those found in the chromosomal DNA
    • They lack mitochondria, chloroplasts and other membrane-bound organelles found in eukaryotic cells

  • Some bacteria also have a flagellum (singular) or several flagella (plural). These are long, thin, whip-like tails attached to bacteria that allow them to move
  • Examples of bacteria include:
    • Lactobacillus (a rod-shaped bacterium used in the production of yoghurt from milk)
    • Pneumococcus (a spherical bacterium that acts as the pathogen causing pneumonia)

A typical bacterial cell, IGCSE & GCSE Biology revision notes

A typical bacterial cell

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Alistair

Author: Alistair

Expertise: Biology & Environmental Systems and Societies

Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.