Fermentation makes no more ATP beyond the small yield from glycolysis. The remaining reactions ________.a. regenerate FADb. regenerate ${\mathrm{NAD}}^{+}$c. regenerate NADHd. regenerate ${\mathrm{FADH}}_2$

Key Concepts: Fermentation, Atp, Glycolysis, Nad+, Nadh, Fad, Fadh2 Explanation: Fermentation occurs in the absence of oxygen and yields ATP by substrate-level phosphorylation during glycolysis. The remaining reactions regenerate NAD+ from NADH to allow for the continuation of glycolysis. Failure of the regeneration of NAD+ will stop glycolysis, and ATP synthesis will cease. Thus, option b. regenerate NAD+ is correct. Step by Step Solution: Step 1. Under anaerobic conditions, glycolysis generates a net of two ATP molecules and two molecules of reduced NAD+ (NADH). Step 2. In the absence of oxygen, there is limited NAD+ to oxidize the NADH generated in step 1. Step 3. To allow for the continuation of glycolysis, the remaining reactions regenerate NAD+ from NADH. Step 4. Since substrate-level phosphorylation produces ATP during glycolysis, the remaining reactions do not produce additional ATP. Step 5. Hence, option b. regenerate NAD+ is correct. Final Answer: b. regenerate NAD+