Question

question 25
if an aerobic organism stopped taking in oxygen, which process would stop first?
○ a. the splitting of glucose into two pyruvates
○ b. the release of carbon dioxide
○ c. the reduction of nad+ to nadh
○ d. the initiation of the krebs cycle
○ e. electron transport chain (etc)

Explanation:

• Option a: Glycolysis (splitting of glucose into two pyruvates) is an anaerobic process and does not require oxygen.
• Option b: Carbon - dioxide release occurs in the Krebs cycle. But the Krebs cycle can continue for a short while as long as there is a supply of acetyl - CoA and other intermediates, and it is not the first to stop when oxygen is cut off.
• Option c: The reduction of NAD+ to NADH occurs in glycolysis (anaerobic) and the Krebs cycle. Glycolysis can still produce NADH without oxygen.
• Option d: The Krebs cycle can function as long as there is a supply of acetyl - CoA (from pyruvate oxidation, which can occur for a short time without oxygen due to the build - up of pyruvate) and other intermediates.
• Option e: The electron transport chain (ETC) is strictly aerobic. Oxygen is the final electron acceptor in the ETC. Without oxygen, the ETC cannot function because there is no molecule to accept the electrons at the end of the chain, and the flow of electrons (and thus the generation of the proton - motive force) stops.

Answer:

e. electron transport chain (ETC)