What is the primary function of a semi-permeable membrane?

The primary function of a semi-permeable membrane is to allow selective passage of water and solutes. This type of membrane is designed to permit certain molecules or ions to pass through while restricting others, creating a balance of substances in different environments.

In biological systems, for instance, cell membranes are semi-permeable, enabling essential processes like osmosis and diffusion. Water and small solutes can move across the membrane, which is crucial for maintaining homeostasis within cells and supporting the various functions that depend on concentration gradients. This selective permeability is essential for numerous physiological processes, including nutrient absorption and waste removal.

Other options describe different scenarios that don't accurately characterize the function of a semi-permeable membrane, such as allowing complete passage of all substances or preventing any passage at all, which would contradict the inherent nature of these membranes. Additionally, while membranes play a role in energy production by creating gradients across them, their primary function is not to facilitate energy production directly.