Which stage(s) of cellular respiration will NOT occur in the absence of oxygen?Group of answer choicesglycolysisoxidative phosphorylationcitric acid cyclepyruvate oxidation

In the absence of oxygen, the stages of cellular respiration that will NOT occur are oxidative phosphorylation, citric acid cycle, and pyruvate oxidation.

Here's why:

1. Glycolysis: This is the first stage of cellular respiration and it does not require oxygen. It occurs in the cytoplasm and breaks down glucose into two molecules of pyruvate, producing a small amount of ATP and NADH in the process.

2. Pyruvate Oxidation: This stage requires oxygen. In the presence of oxygen, pyruvate is transported into the mitochondria where it is oxidized to form Acetyl CoA, releasing CO2 and NADH.

3. Citric Acid Cycle (also known as Krebs Cycle or TCA Cycle): This stage also requires oxygen. It takes place in the mitochondria where Acetyl CoA is further broken down to produce CO2, ATP, NADH, and FADH2.

4. Oxidative Phosphorylation: This is the final stage of cellular respiration and it definitely requires oxygen. It occurs in the inner mitochondrial membrane where the NADH and FADH2 produced in the previous stages are used to generate a large amount of ATP. Oxygen acts as the final electron acceptor in the electron transport chain, forming water.

So, without oxygen, only glycolysis can occur, and the cell would switch to fermentation to regenerate the NAD+ needed for glycolysis.