What property of the cell membrane allows it to regulate the movement of substances?

The property of the cell membrane that allows it to regulate the movement of substances is selectivity. The cell membrane is often described as a selectively permeable barrier, meaning that it can control what enters and exits the cell. This selectivity is crucial for maintaining homeostasis, as it enables the cell to take in necessary substances, such as nutrients, while keeping out harmful materials or toxins.

Selectivity is primarily due to the structure and composition of the cell membrane, which consists of a phospholipid bilayer with embedded proteins. These proteins can act as channels or carriers that facilitate the transport of specific molecules, while preventing others from passing through. This selective nature ensures that only certain molecules can cross the membrane, often based on size, charge, and chemical properties.

In contrast, permeability refers to the ability of the membrane to allow substances to pass through, diffusion is the process by which molecules spread from areas of high concentration to areas of low concentration, and fluidity describes how easily the components of the membrane can move. While these properties are related and contribute to the overall functioning of the cell membrane, selectivity specifically highlights the membrane's regulatory role in controlling substance movement.