What is the outermost layer of a cell called?

The outermost layer of a cell is known as the cell membrane. This structure is crucial as it serves as a protective barrier that confines the cell's contents, maintaining the integrity of the cellular environment. The cell membrane is primarily composed of a phospholipid bilayer, which allows it to be selectively permeable. This means it controls the movement of substances in and out of the cell, facilitating communication and signaling between the cell and its surroundings.

Cell walls, which are rigid structures found outside the cell membrane in plant cells and some bacteria, are not present in animal cells, making them different from the membrane. The nucleus, on the other hand, is an organelle that contains the cell's genetic material, while cartilage is a type of connective tissue found in various parts of the body, not a cellular layer. Thus, understanding the role and structure of the cell membrane is essential in cell biology and directly relates to the functions and health of cells in skin and other tissues.