Identify the longest part of the bacterial flagellum.

The correct answer is Filament.

Key Points

• The motile bacterias have thin filamentous extensions from their cell wall called flagella. 
• Bacteria show a range in the number and arrangement of flagella.
• The bacterial flagellum is made up of three parts:
  1. Filament 
  2. Hook
  3. Basal body
• The filament is the longest portion and extends from the cell surface to the outside.
• This filament consists of Protein which is known as a bacteria cytoskeleton.

Additional Information

• Flagellum
  • It is primarily a motility organelle that enables movement and chemotaxis.
  • Bacteria can have one flagellum or several, and they can be either polar (one or several flagella at one spot) or peritrichous (several flagella all over the bacterium).
• Gram-negative bacteria
  • The example of the bacteria Escherichia coli and Salmonella swim by rotating helical filamentous organelles called the flagellum.
  • The flagellum rotates at a speed of 200–300 Hz driven by a reversible rotary motor embedded in the cell membrane at the base of the filament.