What structure divides the cell's inner components from the outside environment?

The cell membrane, also known as the plasma membrane, is the outermost covering of a cell. It separates the cell's interior from the surrounding environment and is composed of a phospholipid bilayer embedded with proteins. The cell membrane is selectively permeable, meaning it regulates the flow of molecules into and out of the cell. Therefore, the correct answer is the cell membrane. The cell wall is present in plant cells and bacteria and provides structural support, but it does not divide the cell's inner components from the outside environment. The cytoplasm is the gel-like substance that fills the cell's interior, and the nucleus is a membrane-bound organelle that contains the cell's genetic material.