Question

the ethanol produced is the psychoactive ingredient in alcoholic beverages. the co₂ produced by this pathway makes bread rise and beer bubble.
when pyruvate acts as an electron acceptor during fermentation in your muscles, it is reduced and nadh is oxidized, yielding lactic acid and nad⁺.
true
false
when oxygen is depleted in your muscles and cellular respiration shuts down, fermentation begins so atp production can continue. how much atp does fermentation produce per glucose molecule compared to the amount of atp produced by cellular respiration per glucose molecule?
~5%
~50%
~90%
if your muscles become depleted of oxygen after strenuous exercise and switch to fermentation, you can continue activity for a short while. but then you will need to rest (or you will collapse). as you rest, oxygen levels will build back up. when this happens, the lactic acid that has built up during fermentation is converted back to pyruvate. what happens to this pyruvate, now that o₂ is again available?
fermentation continues because the pyruvate is converted back to lactic acid, so nad⁺ is regenerated and glycolysis can continue.
pyruvate is a waste product with no further value to the cell, so is broken down and excreted in urine.
cellular respiration resumes because the pyruvate is processed to feed the citric acid cycle and etc.

Explanation:

• First question: In muscle fermentation, pyruvate acts as an electron acceptor. It is reduced (gains electrons) and NADH is oxidized (loses electrons), forming lactic acid and NAD⁺. This is a key part of lactic - acid fermentation in muscles.
• Second question: Cellular respiration (aerobic) produces about 30 - 32 ATP per glucose molecule, while fermentation (anaerobic, like lactic - acid fermentation) produces only 2 ATP per glucose molecule. \(\frac{2}{32}\approx6.25\%\) (approximate value, and considering typical textbook values for comparison), so it is about 5% of the ATP produced by cellular respiration.
• Third question: When oxygen is available again, the cell will resume cellular respiration. Pyruvate is not a waste product in the presence of oxygen. It enters the mitochondria, is converted to acetyl - CoA, and then enters the citric acid cycle (Krebs cycle) and the electron transport chain (ETC) for further ATP production. Fermentation is an anaerobic (no - oxygen) process, so it will not continue when oxygen is available.

Answer:

• First question: True
• Second question: ~5%
• Third question: Cellular respiration resumes because the pyruvate is processed to feed the citric acid cycle and ETC.