In the context of the study concerning cellular transport in animal cells affected by mitochondrial disease, the method of cellular transport that would still function in the affected animal cells is passive transport.
Passive transport, which includes processes such as simple diffusion and facilitated diffusion, does not require ATP. It relies on concentration gradients to allow molecules to move across the cell membrane. Since mitochondrial disease affects the ability to produce ATP, processes that rely directly on ATP, such as active transport, would be impaired. However, passive transport mechanisms would continue to function as they do not require energy input from ATP.