What process occurs in box 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. pyruvate from this stage is used in a cycle in box b, which is located in the mitochondrion. as a result, atp, co2, and electrons carried by nadh and fadh2 are released. 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. what process occurs in box 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. pyruvate from this stage is used in a cycle in box b, which is located in the mitochondrion. as a result, atp, co2, and electrons carried by nadh and fadh2 are released. 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. electron transport the citric acid cycle glycolysis oxidative phosphorylation electron transport and oxidative phosphorylation