What do all cells have that encloses their cytoplasm and genetic material?

The plasma membrane is a fundamental structure that surrounds all cells, serving as a barrier that encloses the cytoplasm and genetic material. It is composed primarily of a phospholipid bilayer with embedded proteins, which helps regulate the movement of substances in and out of the cell. This selective permeability is crucial for maintaining the cell's internal environment, allowing necessary nutrients to enter while keeping harmful substances out.

While some cells, like plant cells and bacterial cells, have a cell wall that provides additional structure and support, not all cells possess this feature. The nucleus, while important for storing genetic information in eukaryotic cells, is not present in prokaryotic cells, which still have a plasma membrane. The endoplasmic reticulum is an organelle involved in protein and lipid synthesis, but it does not enclose the entire cell. Therefore, the plasma membrane is the universal feature that all cells share to enclose their contents.