Each carrier in the electron transport chain is first _ and then _.

Explanation

In the electron transport chain, the carriers are responsible for shuttling electrons from one component to another. They first accept electrons, which results in their reduction (gain of electrons), and then pass those electrons along to the next carrier, which leads to their oxidation (loss of electrons). This process of sequential reduction and oxidation reactions is essential for the transfer of energy and the generation of ATP in cellular respiration. The electrons are eventually passed to the final electron acceptor, which is typically oxygen, and are used in the production of water.