Fence protects the Yard & Membrane protects the Cell.
Fence surrounds the Yard and allows the certain objects in & out of it whereas a Membrane surrounds the Cell & only allows specific nutrients inside of it.
Given Transition is to Change, and we know that Transition and change are Synonyms. Similarly, Immobility means not moving and synonym of immobility are motionlessness, stillness,...
Hence, Transition is to change as immobility is to stillness.