In 1906 Harden and Young, in a series of classic studies on the fermentation of glucose to ethanol and CO2 by extracts of brewer's yeast, made the following observations.

(A) Inorganic phosphate was essential to fermentation; when the supply of phosphate was exhausted, fermentation ceased before all the glucose was used.
(B) During fermentation under these conditions, ethanol, CO2, and a sugar phosphate accumulated.
(C) When arsenate was substituted for phosphate, no sugar phosphate acumulated, but the fermentation proceeded until all the glucose was converted to ethanol and CO2.

Answer the following questions.

1. Which enzyme of glycolysis requires inorganic phosphate and therefore stops when no phosphate is available?
(a) glyceraldehyde 3-phosphate dehydrogenase
(b) phosphoglycerate mutase
(c) phosphofructokinase-1
(d) phosphoglycerate kinase

2. What sugar phosphate accumulates under these conditions?
(a) glucose 1,6-biphosphate
(b) glucose 1-phosphate
(c) fructose 1-phosphate
(d) fructose 1,6-biphosphate

3. Arsenate substitution for phosphate generated an acyl arsenate compound that immediately degraded. What glycolysis intermediate was a product of the spontaneous degradation of this acyl arsenate?
(a) glycerol 3-phosphate
(b) 3-phosphoglycerate
(c) dihydroxyacetone phosphate
(d) glyceraldehyde 3-phosphate