What process occurs in Box A?

a. A scheme of cellular respiration. At box A, which is located in the cytosol, glucose turns into pyruvate with release of ATP and electrons carried by NADH.

b. Pyruvate from this stage is used in a cycle in box B, which is located in the mitochondrion.

c. As a result, ATP, CO2, and electrons carried by NADH and FADH2 are released.

d. The electrons carried by NADH and FADH2 from boxes A and B are used in box C (inside the mitochondrion) for transformation of a substance marked D (that comes from the cytosol) into a substance marked E (released to the cytosol) with release of ATP.

Glycolysis is the pathway by which glucose, a six-carbon molecule is oxidized to molecules of pyruvate, a three-carbon molecule with the release of ATP and electrons which are carried by NADH molecules.

The process occurs in the cytoplasm of cells and requires 10 glycolytic enzymes.

The pyruvate molecules from glycolysis is first oxidized to acetyl-CoA and carbon dioxide molecules. The acetyl-CoA molecules enter the citric acid cycle occurring in the mitochondria and are used up in the production of ATP, CO2, and electrons carried by NADH and FADH2.

The electrons carried by NADH and FADH2 from glycolysis and citric acid cycle are used in the oxidative phosphorylation pathway occurring inside the mitochondrion for transformation of oxygen molecules into water molecules with release of ATP.