Question

part b - anaerobic conditions and acetyl coa formation
under anaerobic conditions (a lack of oxygen), the conversion of pyruvate to acetyl coa stops.
which of these statements is the correct explanation for this observation?
view available hint(s)
oxygen is required to convert glucose to pyruvate in glycolysis. without oxygen, no pyruvate can be made.
oxygen is an input to acetyl coa formation.
in the absence of oxygen, electron transport stops. nadh is no longer converted to nad+, which is needed for the first three stages of cellular respiration.
atp is needed to convert pyruvate to acetyl coa. without oxygen, no atp can be made in oxidative phosphorylation.

part c - cellular respiration and a cells demand for atp
the rate of cellular respiration is regulated by its major product, atp, via feedback inhibition. as the diagram shows, high levels of atp inhibit phosphofructokinase (pfk), an early
thus atp production decreases. feedback inhibition enables cells to adjust their rate of cellular respiration to match their demand for atp.

Explanation:

In anaerobic conditions (lack of oxygen), the electron transport chain stops. NADH is no longer converted to NAD+ in the electron transport chain. NAD+ is required for glycolysis (the first stage of cellular respiration, which produces pyruvate) and the conversion of pyruvate to acetyl - CoA. Without NAD+ (because its regeneration via electron transport (which requires oxygen as the final electron acceptor) is halted), the conversion of pyruvate to acetyl - CoA (which also needs NAD+ in the pyruvate dehydrogenase complex reaction) stops.

• The first option is wrong because glycolysis (converting glucose to pyruvate) does not require oxygen.
• The second option is wrong because oxygen is not a direct input to acetyl - CoA formation.
• The fourth option is wrong because the issue with acetyl - CoA formation in anaerobic conditions is not directly about ATP for the pyruvate - to - acetyl - CoA conversion (the main issue is the lack of NAD+ due to electron transport chain stopping).

Answer:

In the absence of oxygen, electron transport stops. NADH is no longer converted to NAD+, which is needed for the first three stages of cellular respiration.