When oxygen is present, acetyl-CoA is produced from the pyruvate molecules created from glycolysis. Once acetyl-CoA is formed, aerobic or anaerobic respiration can occur. When oxygen is present, the mitochondria will undergo aerobic respiration which leads to the Krebs cycle.

Answer is mitochondria because it is power house of cell and is responsible for the formation of atp

The correct answer is option 'C': Mitochondria.

Explanation:

The breakdown of the pyruvate molecule using oxygen takes place in the mitochondria during aerobic respiration. Aerobic respiration is the process by which cells break down glucose to produce energy in the presence of oxygen. It occurs in three main stages: glycolysis, the Krebs cycle (also known as the citric acid cycle), and the electron transport chain.

1. Glycolysis:
Glycolysis is the first stage of aerobic respiration and occurs in the cytoplasm of the cell. During glycolysis, glucose is broken down into two molecules of pyruvate. This process occurs in the cytoplasm and does not require oxygen. Glycolysis produces a small amount of ATP (adenosine triphosphate) and NADH (nicotinamide adenine dinucleotide).

2. Pyruvate Decarboxylation:
After glycolysis, the next step is the conversion of pyruvate into a molecule called acetyl-CoA. This step occurs in the mitochondria. Pyruvate is transported from the cytoplasm into the mitochondria through specialized transport proteins. Once inside the mitochondria, pyruvate undergoes decarboxylation, which removes a carbon atom in the form of carbon dioxide. The remaining two-carbon molecule combines with coenzyme A to form acetyl-CoA.

3. Krebs Cycle:
The acetyl-CoA produced in the previous step enters the Krebs cycle, also known as the citric acid cycle. This cycle takes place in the mitochondria. During the Krebs cycle, the acetyl-CoA is further broken down, releasing energy in the form of ATP, NADH, and FADH2 (flavin adenine dinucleotide).

4. Electron Transport Chain:
The final stage of aerobic respiration is the electron transport chain, which also occurs in the mitochondria. The high-energy electrons from NADH and FADH2 produced in the previous steps are transferred through a series of protein complexes in the inner mitochondrial membrane. This transfer of electrons generates a proton gradient, which is used to produce ATP through a process called oxidative phosphorylation.

In summary, the breakdown of the pyruvate molecule using oxygen takes place in the mitochondria during aerobic respiration. The mitochondria are the powerhouses of the cell and are responsible for the majority of ATP production in aerobic organisms.