What is the outer, protective, and semipermeable covering of a cell called?

The outer, protective, and semipermeable covering of a cell is referred to as the cell membrane. This structure plays a crucial role in maintaining the integrity of the cell by regulating what enters and exits, thus enabling the cell to maintain homeostasis. The cell membrane is primarily composed of a phospholipid bilayer that includes various proteins, cholesterol, and carbohydrates, making it flexible and selectively permeable. This means that while it allows essential substances, such as nutrients and ions, to pass through, it also protects the cell from harmful substances.

In contrast, the cell wall, which is a rigid structure found in plant cells, fungi, and some bacteria, provides additional support and protection but is not semipermeable in the same way as the cell membrane. Cytoplasm refers to the gel-like substance within the cell that contains organelles and is involved in cellular processes. The nucleus, on the other hand, is the control center of the cell, containing the genetic material but not serving as the protective outer layer. Thus, the cell membrane is accurately described as the outer, protective, and semipermeable covering of a cell.