Immediately after pyruvate is formed through glycolysis, it enters the mitochondria. Here, it undergoes a reaction to form the following products:

The reaction, known as the "intermediate step" or "pyruvate dehydrogenase complex (PDC)" can be summarized as:

Pyruvate is a three-carbon molecule that forms a two-carbon acetyl-CoA and a molecule of carbon dioxide.

The Krebs cycle begins with the combination of oxaloacetate with acetyl-CoA and produces .  is not product of the Krebs cycle, but a reactant.

Under anaerobic conditions, the 2 molecules of pyruvate produced from glycolysis cannot undergo further oxidation; therefore, they are reduced to lactate (lactic acid) and . This allows glycolysis to continue in order for cells to produce ATP under anaerobic conditions. Once  is cycled back through glycolysis, glucose metabolism can continue to produce 2 net molecules of ATP for cellular energy.

Upon completion of the citric acid cycle, 1 molecule of , 2 molecules of , 3 molecules of , and 1 molecule of  are produced.  is not produced during the citric acid cycle.  is the product of the pentose phosphate pathway.  is a powerful reducing agent used in several metabolic pathways. For example, it is used in red blood cells to reduce glutathione. Note that the products listed above represent those from one turn of the citric acid cycle; each molecule of glucose produces two molecules of acetyl-CoA, thus the cycle turns twice per glucose molecule.

Three carbon dioxide molecules are produced during the cellular respiration if we start with one molecule of pyruvate. The first is made when pyruvate is converted to acetyl-CoA (intermediate step/pyruvate dehydrogenase). The second is produced when D-isocitrate is converted to alpha-ketoglutarate. The third and last is produced when alpha-ketoglutarate is converted to succinyl-CoA. The later two are produced in the citric acid cycle.

The Krebs cycle takes place in the mitochondria. The Golgi apparatus packages substances in order for them to be sent to their appropriate locations, and the chloroplast is where photosynthesis takes place. The nucleus contains DNA and is the site of transcription.

Acetyl-CoA is formed when two carbon atoms join to coenzyme A. Ribose is a five carbon sugar in RNA. ATP is an energy compound, and FAD is an electron carrier in the Krebs cycle which gets reduced then passes its electron to an enzyme complex in the electron transport chain.

Carbon dioxide is the gas produced in the Krebs cycle, which animals exhale. Oxygen is used as an electron acceptor, while nitrogen is not a waste gas. Carbon monoxide is not a waste product in the Krebs cycle. 

The Krebs cycle involves aerobic respiration because oxygen is used. Anaerobic respiration involves fermentation because oxygen is lacking and the compound does not enter the Krebs cycle. Glycolysis is the first step in respiration, which precedes the Krebs cycle and is fully anaerobic. Note that oxygen is not directly required for the Krebs cycle (it is not a reactant), however, without oxygen, the electron transport chain will not proceed and thus the Krebs cycle will also be halted.

The two main products that result from the breakdown of glucose are carbon dioxide and water. Carbon dioxide is produced during pyruvate dehydrogenase and the Krebs cycle. Water is formed at the end of the electron transport chain where two electrons (hydrogens) are added to oxygen (the final electron acceptor).