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Prokaryotic Organisms (Edexcel GCSE Biology: Combined Science)
Revision Note
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
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