Question

after glycolysis, the pyruvate molecules can follow two different metabolic routes: aerobic and anaerobic respiration. what is the main difference between these?
a) anaerobic respiration does not occur in mammalian cells
b) anaerobic respiration does not need oxygen to occur and aerobic respiration does
c) they are the same metabolic pathway, occurring in different locations
d) aerobic respiration occurs in the presence of oxygen and anaerobic respiration is inhibited in its presence

Explanation:

• Option a is incorrect because anaerobic respiration (like lactic acid fermentation) occurs in mammalian muscle cells during oxygen deprivation.
• Option c is incorrect because they are distinct metabolic pathways with different end products and energy yields.
• Option b is incomplete; while anaerobic respiration does not require oxygen, aerobic respiration's reliance on oxygen is only part of the key difference. The full main difference is that aerobic respiration requires oxygen (and uses it as the final electron acceptor), while anaerobic respiration not only does not require oxygen but is also inhibited when oxygen is present.
• Option d correctly states the core distinguishing factor: aerobic respiration depends on oxygen, and anaerobic respiration cannot proceed when oxygen is available.

Answer:

d) Aerobic respiration occurs in the presence of oxygen and anaerobic respiration is inhibited in its presence