Final answer:
The glycerol phosphate shuttle operates in the cytoplasm, facilitating the transfer of electrons into the mitochondria for eukaryotic cells. In prokaryotic cells, the electron transport systems are located in the cytoplasmic membrane.
Step-by-step explanation:
The glycerol phosphate shuttle is primarily found in the cytoplasm and is involved in the transport of electrons from NADH in the cytosol into the mitochondria, where the electron transport chain is located. This shuttle system operates to move the reducing equivalents of NADH into the mitochondria because NADH itself cannot cross the mitochondrial membrane. The electrons from NADH are transferred to dihydroxyacetone phosphate, forming glycerol 3-phosphate, which can then be oxidized in the mitochondrial membrane, transferring the electrons to the electron transport chain. As for prokaryotes, which do not have mitochondria, the location of their electron transport systems is the cytoplasmic membrane (D).