AP BIOLOGY

Detailed explanation-1: -In the presence of oxygen, the next stage after glycolysis is oxidative phosphorylation, which feeds pyruvate to the Krebs Cycle and feeds the hydrogen released from glycolysis to the electron transport chain to produce more ATP (up to 38 molecules of ATP are produced in this process).

Detailed explanation-2: -The Krebs cycle, by itself, does not require the presence of oxygen; this element is necessary for the last stage of aerobic cellular respiration, i.e., oxidative phosphorylation. Organic molecules endowed with energy (carbohydrates, lipids, proteins) are split in previous reactions.

Detailed explanation-3: -If oxygen is NOT present, glycolysis is followed by fermentation.

Detailed explanation-4: -The energy released by this breakdown is carried by NADH. The Krebs cycle completes the breakdown of glucose begun in glycolysis. If oxygen is present, pyruvate enters the mitochondria and is converted to AcetylCoA.

Detailed explanation-5: -If oxygen is available, glycolysis is followed by two processes in the mitochondria–the Krebs cycle and oxidative phosphorylation, respectively–that further increase ATP yield.