(a) Krebs cycle (Citric Acid Cycle) is a key part of cellular respiration and takes place in the mitochondrial matrix. (b) Ubiquinone (Coenzyme Q) is a lipid-soluble mobile carrier in the electron transport chain within the inner mitochondrial membrane. (c) Glycolysis is the initial metabolic pathway in cellular respiration and occurs in the cytoplasm. (d) Acetyl-CoA is formed in the mitochondrial matrix from pyruvate (which is produced during glycolysis in the cytoplasm and then transported into the mitochondria). Thus, pyruvate diffuses from the cytoplasm into the mitochondria where it is converted to Acetyl-CoA.