Final answer:
In prokaryotes, hydrogen ions are pumped by the electron transport system to the outside of the plasma membrane.
Step-by-step explanation:
In prokaryotes, hydrogen ions are pumped by the electron transport system of photosynthetic membranes to the outside of the plasma membrane. This is known as chemiosmosis and is similar to the process that occurs in the mitochondrion. In eukaryotic mitochondria, hydrogen ions flow from the intermembrane space to the mitochondrial matrix.