What term refers to the semi-permeable nature of the cell membrane?

The term that refers to the semi-permeable nature of the cell membrane is "selectively permeable." This characteristic means that the cell membrane allows certain substances to pass through while blocking others. This selectivity is crucial for maintaining the internal environment of the cell, allowing it to regulate the intake of nutrients and the expulsion of waste products.

Selectively permeable membranes are fundamental to the processes of cellular communication and transport, ensuring that essential molecules, such as water, ions, and small organic molecules, can enter or exit the cell's interior, while larger or harmful substances are kept out. This property is vital for the overall homeostasis of the cell, enabling it to function efficiently in varying external conditions.

Other terms such as diffusion and osmosis relate to the movement of substances across membranes but do not specifically describe the selective property of the membrane itself. Equilibrium refers to a state where movement in and out of the cell is balanced, but it does not define the membrane's selective nature. Hence, "selectively permeable" accurately describes how the cell membrane operates to maintain its integrity and functionality.