Question

When oxygen is present, oxidative respiration follows glycolysis, and large amounts of ATP are produced. Which process would most likely occur if the level of oxygen is reduced or absent?

a. fermentation
b. glycolysis
c. Kreb's cycle
d. photosynthesis

Answer 1

When oxygen is scarce or absent, fermentation follows glycolysis to allow continued ATP production. Fermentation uses pyruvate from glycolysis to regenerate NAD+, resulting in lactic acid or ethanol and CO2 as by-products.

Step-by-step explanation:

When oxygen levels are reduced or absent, the process that would most likely occur is fermentation. This term, sometimes called 'anaerobic respiration,' allows for ATP production to continue albeit at a reduced efficiency compared to aerobic respiration.

During fermentation, the pyruvate generated from glycolysis doesn't enter the Krebs cycle but instead undergoes a separate process to regenerate NAD+, which is crucial for glycolysis to persist. Although this pathway produces less ATP, it's vital for cells to maintain energy production when oxygen is scarce.

Fermentation includes the conversion of pyruvate into lactic acid or ethanol, depending on the type of fermentation, and is a common process in both human affairs (such as in the production of yogurts, breads, and alcoholic beverages) and in bodily functions, like the production of energy under anaerobic conditions in muscle cells.