19. Under anaerobic conditions, yeast produce ethanol by fermentation of pyruvate at the end of glycolysis. Why? (2.5 points)(A)Pyruvate to ethanol fermentation reduces toxic CO2 levels.(B)Glycolysis substrate-level phosphorylation changes pyruvate to ethanol.(C)Ethanol produced from pyruvate regenerates NAD+, which is necessary for starting new rounds of glycolysis.(D)To add electrons (and protons) to ethanol for making lactate.

22. Which one is incorrect? (2.5 points)(A)Vitamins are often precursors to coenzymes.(B)Vitamins are small biomolecules that are needed in small amounts in the diets of higher animals.(C)The water-soluble vitamins are vitamin C (ascorbate, an antioxidant) and the vitamin B complex (components of coenzymes).(D)Ascorbate is required for the hydroxylation of proline residues in collagen, a key protein of connective tissue.(E)The water-soluble vitamins are vitamin A (a precursor of retinal), D (a regulator of calcium and phosphorus metabolism), E (an antioxidant in membranes), and K (a participant in the carboxylation of glutamate).

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