Prokaryotic Bacteria cell and its many Components

Classifications of Bacteria

Bacteria are the smallest cellular organisms and are prokaryotes. They can be identified in three ways, judging their shape, whether they are Gram-positive or negative and the way they move.



Cocci Bacteria

– Sphere Shaped

Bacillus Bacteria

– Rod Shaped

Spirillum Bacteria

– Spiral Shaped


Gram Staining

Gram-Positive turn Violet, Gram-Negative turn Red

There are also differences other than shape, these include whether the bacteria is Gram-positive or Gram-negative. Gram-positive bacteria turn violet in colour when Gram stained, whereas Gram-negative bacteria absorb the red counter-stain because the size of the peptidoglycan (murein) layer. The Gram-positive bacerial peptidoglycan layer is between 20 and 80 nanometers wide compared with 7 to 8 with Gram-negative bacteria.

As the ‘gram’ part comes from the stain used by Hans Christian Gram it should always have a capital ‘G’.



Below is a set of slides which go beyond what we have covered so far. They cover growing bacteria, the lifecycle of bacteria and how a fermenter works.

WJEC A2 Biology By4.4 Microbiology from Matthew Higgins