What is the name of the selectively permeable membrane that encloses the cell's cytoplasm?

The selectively permeable membrane that encloses the cell's cytoplasm is known as the cell membrane, also referred to as the plasma membrane. This membrane functions as a barrier, regulating the movement of substances into and out of the cell. Its selective permeability ensures that essential molecules, such as nutrients, can enter the cell, while waste products are removed. The structure of the cell membrane, composed mainly of a phospholipid bilayer with embedded proteins, allows it to maintain the appropriate internal environment for cellular processes while protecting the interior from potentially harmful substances.

The cell wall, for example, is a rigid structure found in plant cells and some prokaryotes, but it does not have selective permeability in the same way that the cell membrane does. The nuclear membrane surrounds the nucleus and is involved in regulating the exchange of materials in and out of the nucleus, but it does not enclose the entire cell. The endoplasmic reticulum is an organelle involved in protein and lipid synthesis, but it is not a membrane that surrounds the cell's cytoplasm. Thus, the cell membrane is the only answer that correctly identifies the membrane that encloses the cytoplasm.