Which term describes the selective movement of substances across a membrane?

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Membranes control which substances cross them, and the term for that selective movement is semi-permeable. A semi-permeable membrane allows some particles to pass while blocking others, based on factors like size, charge, or solubility. This differs from simply permeable, which would imply easy passage for many substances without implying selectivity. Osmosis describes the movement of water through a semi-permeable membrane in response to solute differences, not the general idea of selective movement itself. And selective diffusion isn’t a standard term; diffusion is the spread of particles from high to low concentration and doesn’t inherently convey membrane selectivity. So semi-permeable is the best fit for describing selective movement across a membrane.