AP BIOLOGY

Detailed explanation-1: -In the presence of oxygen, under aerobic conditions, pyruvate enters the mitochondria to proceed into the Krebs cycle. The second stage of cellular respiration is the transfer of the energy in pyruvate, which is the energy initially in glucose, into two energy carriers, NADH and FADH2.

Detailed explanation-2: -Glycolysis can take place without oxygen in a process called fermentation. The other three stages of cellular respiration-pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation-require oxygen in order to occur.

Detailed explanation-3: -Oxygen is used as the final electron acceptor in the electron transport chain in eukaryotic cells. This process occurs in the inner mitochondrial membrane and matrix in eukaryotic cells, like in humans. The mitochondria is an organelle with the main purpose of creating energy for the cell.

Detailed explanation-4: -Glycolysis, which is the first step in all types of cellular respiration is anaerobic and does not require oxygen. If oxygen is present, the pathway will continue on to the Krebs cycle and oxidative phosphorylation.