• 14 parts
  • Checked October 2026

Bacterial Cell Wall Structure Diagram

Three bacterial cell walls in section: Gram-positive, Gram-negative and acid-fast.

Bacterial Cell Wall Structure Diagram

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1 2 3 4 5 6 7 8 9 10 11 12 13 14
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Write the name of each numbered part.Answer key

  1. Peptidoglycan
  2. Teichoic acid
  3. Lipoteichoic acid
  4. Plasma membrane
  5. Outer membrane
  6. Lipopolysaccharide
  7. Porin
  8. Peptidoglycan
  9. Periplasm
  10. Plasma membrane
  11. Mycolic acids
  12. Arabinogalactan
  13. Peptidoglycan
  14. Plasma membrane

Drawn for this site on 2026-10-01 from plain geometry. Licence: own work.

Each numbered ring is a button. Use the arrow keys to move between them and Enter to choose. Names are read out in Study, and once a part is answered.

Next step Zoom out: the whole bacterial cell

All 14 parts on the diagram

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Gram-positive wall 4

  1. Peptidoglycan A thick mesh of sugar chains and short peptides. It makes up most of this wall.
  2. Teichoic acid A long chain bound to the peptidoglycan. It runs through the wall and out past the surface.
  3. Lipoteichoic acid A teichoic acid held in the plasma membrane by a lipid. It crosses the whole wall.
  4. Plasma membrane The membrane under the wall. It encloses the cytoplasm.

Gram-negative wall 6

  1. Outer membrane A second membrane outside the thin peptidoglycan layer. Chains of lipopolysaccharide stand on it.
  2. Lipopolysaccharide Chains of sugars on a lipid anchor in the outer membrane. The lipid part is called lipid A, or endotoxin.
  3. Porin A protein channel through the outer membrane. Small molecules pass through it.
  4. Peptidoglycan Only a thin layer here. It lies in the periplasm between the two membranes.
  5. Periplasm The gel-filled space between the outer membrane and the plasma membrane.
  6. Plasma membrane The inner of the two membranes. It encloses the cytoplasm.

Acid-fast wall 4

  1. Mycolic acids Long fatty acids packed into a waxy outer layer. They make up most of this wall.
  2. Arabinogalactan Branched chains of two sugars. They link the peptidoglycan below to the mycolic acids above.
  3. Peptidoglycan A thin inner layer. The arabinogalactan is linked to it.
  4. Plasma membrane The membrane under the wall. It encloses the cytoplasm.

How this list was compiled: Every part was checked on 2026-10-01 and kept only where two independent sources name it. (1) Gary Kaiser, Microbiology, sections 2.3A The Gram-Positive Cell Wall, 2.3B The Gram-Negative Cell Wall and 2.3C The Acid-Fast Cell Wall, an open college textbook, https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(Kaiser)/Unit_1%3A_Introduction_to_Microbiology_and_Prokaryotic_Cell_Anatomy/2%3A_The_Prokaryotic_Cell_-_Bacteria/2.3%3A_The_Peptidoglycan_Cell_Wall/2.3A%3A_The_Gram-Positive_Cell_Wall . (2) Wikipedia, text only: Gram-positive bacteria, https://en.wikipedia.org/wiki/Gram-positive_bacteria ; Gram-negative bacteria; Bacterial cell structure; Teichoic acid; Lipopolysaccharide; Peptidoglycan; Mycobacterium; Mycolic acid. Licence: own work

The drawing: Drawn for this site on 2026-10-01 from plain geometry; nothing traced. Licence: own work

How it works

Each drawing is a slice through the edge of a bacterium, with the outside at the top and the plasma membrane near the bottom. All three walls hold peptidoglycan. What differs is how much, and what lies outside it.

Read the full guide

Thick wall or two membranes

A Gram-positive wall is mostly peptidoglycan, with teichoic acids threaded through it. A Gram-negative wall has only a thin layer, and outside it a second membrane that carries porins and lipopolysaccharide.

The acid-fast wall

Here the thin peptidoglycan is linked to arabinogalactan, and that to a tall layer of mycolic acids. Mycolic acids are long fatty acids, so the outside of this wall is waxy.

  • A teichoic acid stops in the peptidoglycan; a lipoteichoic acid reaches down into the membrane.

Questions and answers

What is the difference between a Gram-positive and a Gram-negative cell wall?

A Gram-positive wall has a thick layer of peptidoglycan with teichoic acids and no outer membrane. A Gram-negative wall has a thin layer of peptidoglycan lying between two membranes, and its outer membrane carries lipopolysaccharide.

Where are endotoxins on a bacterial cell diagram?

In the Gram-negative wall's outer membrane. Endotoxin is another name for lipopolysaccharide, and more exactly for lipid A, the part that anchors each chain in the membrane.

What is an acid-fast cell wall made of?

From the inside out: a thin layer of peptidoglycan, a layer of arabinogalactan linked to it, and an outer layer of mycolic acids. The mycolic acids make up most of the wall.

Why are the walls called Gram-positive and Gram-negative?

The names come from the Gram stain. A thick layer of peptidoglycan holds the stain, so the cell tests positive. A thin layer does not hold it, so the cell tests negative.

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