Cellular Respiration and Enzymes

In the energy conserving phase of glycolysis, the conversion of BPGA to PGA is catalyzed by phosphoglycerate kinase. The phosphate on carbon 1 is transferred to a molecule of ADP, yielding ATP and 3-phosphoglycerate. This type of ATP synthesis, traditionally referred to as substrate-level phosphorylation, involves the direct transfer of a phosphate group from a substrate molecule to ADP, to form ATP.
$1,3-bisphosphoglycerate+ADP\overset{Phosphoglycerate kinase}{\underset{{Mg}^{2+}}{\rightleftharpoons}}3-phosphoglycerate+ATP$

Glycolysis produces 2 ATP, 2 NADH,2 pyruvate molecules. It is the aerobic catabolic breakdown of glucose, which produces energy of 68KJ in form of ATP, NADH, and pyruvate, which itself enters a citric acid cycle to produce more energy.

Glycolysis, part of cellular respiration, is a series of reactions that constitute the first phase of most carbohydrate catabolism. Catabolism means the breaking down of larger molecules into smaller ones. The word glycolysis is derived from two Greek words and means the breakdown of something sweet. Glycolysis breaks down glucose and forms pyruvate with the production of two molecules of ATP. The pyruvate end product of glycolysis can be used in either anaerobic respiration if no oxygen is available or in aerobic respiration via the TCA cycle which yields much more usable energy for the cell.  When oxygen is present, NADH can pass its electrons into the electron transport chain, regenerating NAD$^+$ for use in glycolysis. When oxygen is absent, cells may use other, simpler pathways to regenerate NAD$^+$ these pathways, NADH donates its electrons to an acceptor molecule in a reaction that doesn’t make ATP but does regenerate NAD$^+$ so glycolysis can continue. This process is called fermentation.

During glycolysis process the substrate pyruvic acid is formed from glucose is then oxidized into lactic acid in muscles by pyruvic acid, decarboxylase and alcohol dehydrogenase.

During the process of glycolysis, ATP is utilized and produced but the carbon dioxide and water are not the end products.

NADH is essentially produced only during the cellular respiration and it gets oxidised to release energy in the form of ATP. Glycolysis is a part of cellular respiration and leads to production of NADH. However, photosystem I and II produce NADPH rather than NADH as energy carriers. So the answer is 'Glycolysis'.

Glycolysis takes place in the cytosol of cytoplasm without the involvement of oxygen. The by-product of glycolysis is pyruvate which entered into mitochondria and oxidized oxygen to carbon dioxide.

In glycolysis, the respiratory substrate glucose is oxidised to pyruvic acid to release energy. The enzyme enolase converts phosphoglycerate to phosphoenol pyruvate with the release of H$ _2$O. So, the correct answer is 'Phosphoenol pyruvate'.

There is no utilization oxygen is seen in the process of glycolysis which takes place in the cytoplasm and it is an anaerobic process. After finishing the glycolysis the cell needs to respirate through aerobic respiration in the presence of oxygen. Aerobic reactions occur in the mitochondria which require oxygen.

One molecule of 3-phosphoglyceric acid enters the glycolytic pathway after the initial steps. Its complete oxidation through glycolysis and the Krebs cycle yields 16 ATP molecules.

Fructose-1,6-bisphosphate is already phosphorylated. It bypasses the initial investment phase of glycolysis, resulting in a net gain of 40 ATP molecules upon complete oxidation.

Peter Mitchell proposed a theory to explain the production of ATP which is 'Mitchell's chemiosmotic coupling hypothesis'. According to this theory:

The standard free energy change for the hydrolysis of ATP to ADP and inorganic phosphate is approximately 7.3 to 7.6 kcal/mol under physiological conditions.

Cyanide inhibits cytochrome c oxidase, blocking the electron transport chain and halting ATP production. Injecting ATP provides the necessary energy for vital cellular functions that would otherwise fail.