The inner chloroplast membrane is impermeable to large, polar and ionic compounds such as NADH and ATP. However, the membrane has an antiport protein that facilitates the passage of dihydroxyacetonephosphate or 3-phosphoglycerate in exchange for Pi. The system permits the entry of Pi for photophosphorylation and the exit of the products of carbon fixation. Explain how the same antiport could “transport” ATP and the reduced cofactors from the cytosol.