What is the role of a peptidoglycan layer in bacterial cells?

The peptidoglycan layer plays a crucial role in maintaining the structural integrity and shape of bacterial cells. It is a robust polymer consisting of sugars and amino acids, forming a mesh-like structure that surrounds the cell membrane. This layer provides mechanical support, helping to withstand the internal pressure from the cell's cytoplasm and preventing cell lysis—especially in hypotonic environments where water influx is a concern.

In addition to structural support, the peptidoglycan layer protects the bacterial cell from various environmental stresses, such as changes in osmotic conditions and threats from the host's immune system, including enzymes that target bacterial cells. By providing this protective barrier, it ensures that the bacteria can survive and thrive in varied ecological niches.

Other options focus on different functions that are not primarily linked to the peptidoglycan layer. For instance, nutrient absorption is mainly facilitated by the cell membrane rather than the peptidoglycan layer. While peptidoglycan does help maintain stability, it is not directly involved in water retention or bacterial reproduction, which are processes that involve other cellular structures and mechanisms.