Prokaryotic Cells (Edexcel International A Level Biology)

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Biology & Environmental Systems and Societies

Cell Components: Structures

  • Animal and plant cells are types of eukaryotic cells, whereas bacteria are a type of prokaryote
  • Prokaryotic cells are much smaller than eukaryotic cells 
  • They also differ from eukaryotic cells in having
    • A cytoplasm that lacks membrane-bound organelles
    • Ribosomes that are smaller (70 S) than those found in eukaryotic cells (80 S)
    • No nucleus, instead having a single circular bacterial chromosome that is free in the cytoplasm and is not associated with proteins
    • A cell wall that contains the glycoprotein murein 
      • Murein is sometimes known as peptidoglycan
  • In addition, many prokaryotic cells also have the following structures
    • Loops of DNA known as plasmids
    • Capsules
    • Flagella (singular flagellum)
    • Pili (singular pilus)
    • A cell membrane that contains folds known as mesosomes

Cell Components- Prokaryotic cell

Bacteria are prokaryotic cells

Prokaryotes vs eukaryotes

  • There are a number of important structural and physiological differences between prokaryotic and eukaryotic cells
  • These differences affect their metabolic processes and how they reproduce

Comparison of Prokaryotic and Eukaryotic Cells Table

Comparison of Prokaryotes & Eukaryotes table

Exam Tip

You will need to know all the differences between prokaryotic and eukaryotic cells; remember that not all of the structures mentioned here are present in all prokaryotic cells

Remember that size is not a structural feature so if you are asked for a structural difference between a prokaryotic and eukaryotic cell don't include size in your answer.

Cell Components: Functions

  • The ultrastructure of prokaryotic cells includes several features that are not found in eukaryotic cells, e.g.
    • Plasmids
    • Capsule
    • Flagella
    • Pili
    • Mesosomes
    • Circular DNA
    • Ribosomes
  • Some of these features are found in all prokaryotes, while some are only present in some

Additional Prokaryotic Structures Table


Exam Tip

Note that the specification does not include the role of mesosomes in prokaryotic cells.

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Author: Alistair

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.

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