A thin layer covering the outside of cells?

The thin layer covering the outside of cells is called the cell membrane or plasma membrane. The cell membrane is a vital component of all cells, whether they are prokaryotic (lacking a nucleus) or eukaryotic (containing a nucleus). It serves as a selective barrier that separates the internal environment of the cell from the external environment, controlling the passage of substances in and out of the cell.

The cell membrane is primarily composed of lipids (such as phospholipids), proteins, and carbohydrates. The phospholipid bilayer forms the basic structural framework of the membrane, with proteins embedded within or attached to the surface. These proteins play various roles, including transport of molecules, cell signaling, and maintaining the structural integrity of the membrane.

Overall, the cell membrane is crucial for maintaining cellular homeostasis and allowing cells to interact with their surroundings while protecting their internal components.