Question

identify the byproduct of lactic acid fermentation. (1 point)
○ carbon dioxide
○ pyruvic acid
○ lactic acid
○ oxygen

Explanation:

Lactic acid fermentation is an anaerobic process where pyruvic acid is converted to lactic acid, with no carbon dioxide or oxygen produced. Pyruvic acid is the starting substrate, not a byproduct, and lactic acid is the main product. Wait, correction: actually, in lactic acid fermentation, the only product is lactic acid, but re-evaluating the options, none are perfect, but carbon dioxide is a byproduct of alcoholic fermentation, not lactic. Wait no—wait, no, lactic acid fermentation: glucose → 2 pyruvate → 2 lactic acid, with no other byproducts. But among the options, the only one that fits is that none? No, wait, no, maybe I misremember. Wait no, pyruvic acid is the precursor, oxygen is not involved, lactic acid is the main product. Wait, maybe the question has a typo, but no—wait, no, actually, in some contexts, but no, let's recheck: Lactic acid fermentation: the reaction is $C_3H_4O_3$ (pyruvate) + $NADH$ → $C_3H_6O_3$ (lactic acid) + $NAD^+$. So no carbon dioxide, no oxygen. Pyruvic acid is the reactant, lactic acid is the product. Wait, but the question asks for byproduct. Wait, maybe the question is using "byproduct" incorrectly, but among the options, the only one that is a product (if we consider it) is lactic acid? No, no, wait no—wait, no, alcoholic fermentation produces ethanol and CO2 as byproduct. Lactic acid fermentation only produces lactic acid. Wait, maybe the question is wrong, but let's look again. Wait, no, maybe I made a mistake. Wait, no: glucose is broken down to pyruvate (glycolysis), then pyruvate is converted to lactic acid. So pyruvate is the substrate, lactic acid is the product. No byproducts. But among the options, the only one that is related is lactic acid? No, that's the main product. Wait, no, maybe the question means product instead of byproduct. Then lactic acid is the answer. Because the other options: carbon dioxide is from alcoholic fermentation, oxygen is not involved, pyruvic acid is the starting material.

Answer:

○ lactic acid