Question

question 32
when muscles are exercised vigorously in the absence of oxygen
a. nadh molecules split
b. lactic acid is produced
c. mitochondria become more active
d. a large amount of atp is formed
e. glycolysis stops

Explanation:

When muscles are exercised vigorously without oxygen, anaerobic respiration occurs. In anaerobic respiration in animals (like muscle cells), glycolysis continues (so option e is wrong). NADH is used (not split, so option a is wrong). Mitochondria rely on oxygen - dependent processes (aerobic respiration), and without oxygen, their activity related to energy production from glucose breakdown (in the context of this question) is not enhanced (so option c is wrong). A large amount of ATP is formed in aerobic respiration (about 36 - 38 ATP per glucose), while in anaerobic respiration (lactic acid fermentation in muscles), only 2 ATP per glucose are formed (so option d is wrong). Lactic acid is produced as the end - product of anaerobic respiration in muscle cells.

Answer:

B. lactic acid is produced