Prokaryotic Organisms (Edexcel GCSE Biology)

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