What is the purpose of redox reactions in the cell? to produce nad+ and other electron carriers to produce glucose and other carbohydrates to carry oxygen to cells throughout the body to release energy slowly in a step-by-step process

The correct answer is to discharge energy gradually in a step-by-step process.  

The process of cellular respiration comprises various reactions in which electrons are transferred or mediated from one molecule to another. The reactions taking part in electron transfers are called redox reactions or oxidation-reduction reactions.  

With the movement of electrons the energy is released that can be captivated and is used to do work. In cellular respiration, the electrons from glucose move slowly via the electron transport chain ultimately towards oxygen that is, transferring towards lower and lower energy states and discharging energy at each stage.  

that is wrong, its not thymus.

the answer would be d : p