How does the presence of oxygen affect the chemical pathways used to extract energy from glucose

The presence of oxygen ensures that more energy is extracted from glucose than in the absence of oxygen.

In the presence of oxygen, glucose first undergoes glycolysis during which it is converted into 2 molecules of pyruvates. The pyruvates then enter Kreb's cycle and the resulting electrons travel through the electron transport chain.

A small amount of ATP is generated during glycolysis but more ATP is generated in Kreb's cycle and the electron transport chain.

In the absence of oxygen, however, only glycolysis occurs because oxygen is necessary for Kreb's cycle and the electron transport chain to function. The pyruvate molecules generated are either converted to lactic acid or alcohol.

Thus, the amount of energy generated in the absence of oxygen far falls short of the amount generated in the presence of oxygen.

More on aerobic and anaerobic respiration processes can be found here: link

Explanation:

Glycolysis is the metabolic pathway or cycle that transforms glucose (C6H12O6) into pyruvate, CH3COCOO−, and H+ by producing free energy, this supports in high-energy molecules like ATP (Adenosine triphosphate) and NADH (Nicotinamide adenine di-nucleotide) formation.

The presence of oxygen affect the chemical pathways which is used to extract energy from glucose in glycolysis process as in the presence of oxygen gas all hydrogens stripped off Acetyl CoA, two by two, to remove the electrons for the generation of ATP, until no hydrogen is left and all that remains of sugar is carbon-di-oxide, a waste product and water.

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