Common Features: Prokaryotic Organisms (Edexcel IGCSE Biology)

Prokaryotes

• All living organisms can be grouped, or classified, using a classification system that consists of five kingdoms; these are:

  • animals

  • plants

  • fungi

  • protoctists

  • prokaryotes

• The prokaryotes are different from the other four kingdoms, which are all eukaryotes

• Features of prokaryotic organisms include:

  • they are single-celled

  • they have no nucleus

  • the nuclear material is found in the cytoplasm

• Bacteria are prokaryotic organisms

Bacteria

• Bacteria share the following biological characteristics:

  • they are microscopic, single-celled organisms

  • they have a cell wall, cell membrane, cytoplasm and plasmids

  • they lack a nucleus but contain circular DNA

  • they lack mitochondria and have no other membrane-bound organelles

• 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

• Bacteria feed in different ways:

  • Some bacteria carry out photosynthesis despite having no chloroplasts; this is because they still possess chlorophyl and have the enzymes necessary to synthesise sugars

  • Most feed on other living or dead organisms

    • If they feed on dead organic matter then they are known as saprobionts or decomposers

Bacteria have a cell wall, cell membrane, cytoplasm, plasmids and circular DNA

Components of prokaryotic and eukaryotic cells table