Answer the following question given this paragraph: 

Figure 13.6 Bacteria are divided into two major groups: Gram-positive and Gram-negative. Both groups have a cell wall composed of peptidoglycans: In Gram-positive bacteria, the wall is thick, whereas in Gram-negative bacteria, the wall is thin. In Gram-negative bacteria, the cell wall is surrounded by an outer membrane.


Q: Gram-positive and gram-negative bacteria are distinguished by thickness of what?

 Choices:

- cell membrane

- cell weight

- cell length

- cell wall

A:
cell wall
