Glycolysis is the first step in cellular respiration, and is seen in both aerobic and anaerobic respiration. The products of glycolysis are pyruvate, NADH, ATP, and water. Oxygen is only a product of the light reactions of photosynthesis; it is consumed as a reactant in the electron transport chain.

Glycolysis, which occurs in the cytoplasm, is the first step of cellular respiration. Though it does not produce a large amount of ATP by itself, it incorporates several important steps that must take place to yield a much more significant amount of ATP later. Notable events that occur during this multi-step process include the breakdown of each glucose molecule into two 3-carbon pyruvate molecules, the production of two molecules of , and the net production of two ATP molecules.

Unlike the next two steps (the citric acid cycle and oxidative phosphorylation), glycolysis can occur in the absence of oxygen. The only step given that is not part of glycolysis is the transfer of electrons from carrier molecules to oxygen via a series of steps. This happens during oxidative phosphorylation and, unlike glycolysis, is an aerobic process.

Fermentation is the metabolic process that takes place in anaerobic environments to regenerate for glycolysis, which takes place in both aerobic and anaerobic environments. Since glycolysis is unaffected by the presence of oxygen, pyruvate concentrations will be the same in either environment. During fermentation the cell changes the pyruvate into acetaldehyde. Ethanol is also a product of fermentation. We would not expect to see more acetaldehyde or ethanol in aerobic metabolism.

Adenosine triphosphate (ATP) is the main product of cellular respiration, and the molecular energy of the cell. Aerobic metabolism results in a much higher yield of these energy carrying molecules due to the fact that it can use oxygen as a final electron acceptor in the electron transport chain.

Glycolysis takes place in the cell cytosol, and can take place under anaerobic conditions. After the completion of glycolysis, the product pyruvate is transported to the mitochondria for the citric acid cycle and electron transport chain.

The nucleus houses the cell's DNA, and the endoplasmic reticulum is involved with protein modification.

Glycolysis is the process that converts glucose to pyruvate. It produces a total of four ATP, but consumes two ATP, for a net yield of two ATP. Glycolysis is not dependent on the presence of oxygen and can occur in either aerobic or anaerobic environments.

The citric acid cycle, or Krebs cycle, is used to generate NADH from pyruvate. The NADH is then used in the electron transport chain to generate a proton gradient, which fuels oxidative phosphorylation. Since oxidative phosphorylation requires an oxygen molecule, the citric acid cycle and electron transport chain cannot continue in anaerobic environments.

Glycolysis produces four molecules of ATP, but two molecules are used to complete reactions during the initial steps of the process. With four molecules produced and two molecules consumed in the process, there is a net yield of two ATP from each glucose molecule in glycolysis

During ATP synthesis in the electron transport chain, approximately 32 additional ATP are generated.

Fructose-2,6-bisphosphatase is an enzyme that is responsible for regulating glycolysis and gluconeogenesis. When serine-32 is phosphorylated on fructose-2,6-bisphosphatase, glycolysis is stimulated and gluconeogenesis is inhibited.

Glycolysis produces two molecules of pyruvate and two molecules of NADH. The cell technically produces four molecules of ATP during glycolysis; however, it uses two molecules to initiate the process. The net production of ATP is only two. FADH₂ is produced in the Krebs cycle.

Remember that glycolysis produces a net product of two ATP, two NADH, and two pyruvate molecules. NADH is produced by reducing NAD⁺, and ATP is produced by substrate level phosphorylation of ADP. Pyruvate is a three-carbon molecule that is derived from the six-carbon glucose. The six-carbon glucose is broken down to create two pyruvate molecules (3 carbons each).

During the Krebs cycle pyruvate is further broken down, and some carbons are used to form carbon dioxide.

Pyruvate is an end product of fermentation; however, unlike the pyruvate from glycolysis the pyruvate from fermentation does not go into the Krebs cycle. The pyruvate is either converted into lactic acid or ethanol. Yeast undergoes fermentation, but they produce ethanol from pyruvate, not lactic acid. Finally, fermentation and glycolysis occur in the cytosol of cells, not in the cell membrane.

The only answer choice you are left with is that fermentation converts NADH back into NAD⁺. During anaerobic respiration, glycolysis is used to produce small amounts of ATP. NAD⁺ is used as a reactant in this process, and NADH is a product. Over time, NAD⁺ becomes the limiting reagent if it is not regenerated by the electron transport chain. The primary function of fermentation is to restore this reactant and allow glycolysis to proceed.