The term that identifies the concept that some substances can move freely across a cell membrane while others must be carried by proteins is selective permeability.

Here's why:

* Selective permeability means that the cell membrane allows some substances to pass through while blocking others.

* This is due to the structure of the membrane, which is primarily composed of a phospholipid bilayer.

* Small, nonpolar molecules (like oxygen and carbon dioxide) can easily diffuse across the membrane.

* Larger, polar molecules (like glucose and ions) require the assistance of transport proteins to move across the membrane.

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