In Donnan's equilibrium, the accumulation of non-diffusible ions occurs without expenditure of metabolic energy. The primary requirement/energy source for ion accumulation is:

To test if viral proteins are transported between Golgi stacks in vesicles or are released into the cytosol by one Golgi stack and taken up by another, viral protein transport was examined between Golgi stacks of infected and uninfected cells. Which one of the following experimental designs would best distinguish these two hypotheses?