Questions: The cell wall of Gram-positive bacteria Multiple Choice contains a thin layer of peptidoglycan. contains a thick layer of peptidoglycan. is, due to its thickness, an excellent barrier to most molecules. contains an outer membrane containing LPS. contains a thin layer of peptidoglycan AND contains an outer membrane containing LPS.

The answer is the second one: contains a thick layer of peptidoglycan.

Explanation for each option:

1. Contains a thin layer of peptidoglycan: This is incorrect. Gram-positive bacteria have a thick layer of peptidoglycan in their cell walls, which is a key characteristic that differentiates them from Gram-negative bacteria.

2. Contains a thick layer of peptidoglycan: This is correct. Gram-positive bacteria are characterized by having a thick peptidoglycan layer, which is responsible for retaining the crystal violet stain used in the Gram staining procedure.

3. Is, due to its thickness, an excellent barrier to most molecules: This is incorrect. While the thick peptidoglycan layer provides structural support and protection, it is not an excellent barrier to all molecules. Gram-positive bacteria lack an outer membrane, which makes them more permeable to certain substances compared to Gram-negative bacteria.

4. Contains an outer membrane containing LPS: This is incorrect. Gram-positive bacteria do not have an outer membrane or lipopolysaccharides (LPS). These features are characteristic of Gram-negative bacteria.

5. Contains a thin layer of peptidoglycan AND contains an outer membrane containing LPS: This is incorrect. As mentioned, Gram-positive bacteria have a thick peptidoglycan layer and do not have an outer membrane or LPS.

In summary, the defining feature of Gram-positive bacteria is their thick peptidoglycan layer.