Supercharge your learning!

Use adaptive quiz-based learning to study this topic faster and more effectively.

Bacterial structure: exterior features

Bacteria also possess structures on their outsides to assist with protection, communication and movement.

  • Capsules are made up of polysaccharide polymers and amino acids. A capsule lies outside the cell wall and membrane to protect the bacterium.
  • Pili (singular pilus) are protein filaments around $$0.5-10\text{ }\mu\text{m}$$ in length. They are located on the outside of the cell and allow cells to attach to each other and communicate.
  • Flagella (singular flagellum) are protein filaments around $$3-20\text{ }\mu\text{m}$$ long. They are present on the outside of the bacterial capsule. Flagella allow bacteria to propel themselves.
The pili are shown on the outside of the cell. This gram-positive bacterium has a flagellum.
The pili are shown on the outside of the cell. This gram-positive bacterium has a flagellum.