Common Features: Prokaryotic Organisms (Edexcel IGCSE Biology)

• 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