Which structure is primarily responsible for the selective permeability of a cell?

The cell membrane, also known as the plasma membrane, is primarily responsible for the selective permeability of a cell. This characteristic allows the cell to maintain homeostasis by controlling the movement of substances in and out of the cell. The structure of the cell membrane consists of a double layer of phospholipids along with embedded proteins, which create a barrier that is fluid and dynamic.

These properties enable the membrane to selectively allow certain molecules to pass while restricting others based on factors such as size, charge, and solubility. Transport mechanisms like diffusion, facilitated diffusion, and active transport are all influenced by the structure of the cell membrane, which strategically regulates the exchange of ions, nutrients, and waste products.

Other structures mentioned, such as the cell wall, cytoplasm, and nucleus, do play roles in various cellular functions, but they do not primarily govern the selective permeability. The cell wall, found in plant cells, provides structural support and protection but is not selectively permeable in the same dynamic way as the cell membrane. The cytoplasm is the site for cellular processes but does not contribute to selective permeability. The nucleus houses the genetic material and manages cellular activities, but it does not interact directly with the transport of substances across the cell boundary.