If molecular oxygen is present, the products of glycolysis will continue and be fed into aerobic metabolism: the citric acid cycle and oxidative phosphorylation. If molecular oxygen is absent, glycolysis will lead to anaerobic metabolism/fermentation. Thus, the fate of pyruvate depends on the availability of oxygen.  does need to be recycled for glycolysis to proceed, but this can happen via the electron transport, which can only proceed if oxygen is present. Thus, while this is fundamentally correct, it is a downstream regulator. Coenzyme A is not a limiting factor in the fate of pyruvate, but it does get added after a molecule of carbon dioxide is released, producing acetyl-CoA during pyruvate dehydrogenation. Phosphoric acid and calcium ions are not relevant to this question.

Glucose can be catabolized by both aerobic and anaerobic means. When glucose undergoes oxidative phosphorylation (aerobic metabolism), the end products are carbon dioxide, water, and ATP. In the absence of oxygen, glucose can undergo either lactic acid or alcoholic fermentation. Lactate is a result of lactic acid fermentation, and ethanol and carbon dioxide are results of alcoholic fermentation. 

Glucose goes through glycolysis to form pyruvate molecules which then proceed into the pyruvate dehydrogenase complex.  Acetyl-CoA is created from this, which can then move into the citric acid cycle.  High energy electron carries,  and , that were created in glycolysis and the citric acid cycle finally go through the electron transport chain to pump hydrogens through the mitochondrial membrane.  These hydrogens are used to generate ATP via the ATP synthase.

If a cell is lacking in oxaloacetate, the Krebs cycle will be unable to continue.  Therefore, there will be no way for the electron transport chain to receive the high energy electrons it requires to create ATP.  And so, fermentation will take over in the cell for creation of ATP.  Glycolysis will not stop, but the end product pyruvate will build up because it will only be able to be used for fermentation, not in the pyruvate dehydrogenase complex.

In glycolysis, glucose is broken down. 2 ATP are required for glycolysis to begin, resulting in a creation of 4 ATP. This is a net of 2 ATP. NADH is created from , not the other way around. While 7 of the 10 steps of glycolysis are reversible, the other 3 are irreversible. Finally, if ATP is plentiful, there is no need for glycolysis to speed up (it will actually likely slow down).

Glycolysis is the only of the above choices that occurs in the cytoplasm. The remaining occur in different parts of the mitochondria. The Krebs cycle occurs in the mitochondrial matrix. Both oxidative phosphorylation and the electron transport chain occur along the inner mitochondrial membrane.

 in unrelated to the Krebs cycle and the electron transport chain.  is produced during the pentose phosphate pathway, which is a branch off of glycolysis. The first phase of the pentose phosphate pathway is called the oxidative phase, and is where  is created. During the second phase, five-carbon sugars are created, the most important being ribose-5-phosphate.

In glycolysis, glucose is oxidized, and the final products are 2 pyruvate, 2 ATP, and 2 NADH. The first step is irreversible, and is the conversion of glucose to glucose-6-phosphate by the enzyme hexokinase. The only remaining answer choice is "every step is irreversible." That statement is false. Steps 1,3, and 10 are irreversible, but the remaining steps are reversible.

Fructose is mainly metabolized by the liver from sugar, honey and fruits. Fructose can be converted to fructose-1-phosphate and then to dihydroxyacetone phosphate (DHAP) and glyceraldehyde.

NADPH is a molecule created during the oxidative phase of the pentose phosphate pathway. It is used in anabolic reactions, specifically in the formation of fatty acids. Another important role is that it acts as an anti-oxidant. Finally, NADPH is easily discriminated from NADH in the body because of an additional attached phosphate group. This allows the body to regulate the concentrations of the two similar molecules independently.