Biology CLEP Prep 2025 – 400 Free Practice Questions to Pass the Exam

During cellular respiration, oxygen plays a critical role in the electron transport chain. This is where energy from glucose is converted into ATP, the energy currency of cells. Oxygen accepts electrons from the electron transport chain and combines with hydrogen ions to form water, releasing energy that is used to generate ATP. Option A is incorrect because oxygen does not directly provide energy to the cell. Option B is incorrect because oxygen is not a reactant in the Krebs cycle, but rather in the electron transport chain. Option D is incorrect because oxygen does not store energy for later use but instead helps to produce energy.