'Jettison' means to discard and 'salvage' means to rescue something discarded. Hence, 'salvage' is the word which is farthest in meaning to the given word 'Jettison'.
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.