Figure 13.6 Which of the following statements is true?

1. Gram-positive bacteria have a single cell wall formed from peptidoglycan.
2. Gram-positive bacteria have an outer membrane.
3. The cell wall of Gram-negative bacteria is thick, and the cell wall of Gram-positive bacteria is thin.
4. Gram-negative bacteria have a cell wall made of peptidoglycan, while Gram-positive bacteria have a cell wall made of phospholipids.