Why is pyruvate reduced to lactate when oxygen is not available?

Question

a. Lack of oxygen signals the genes in the nucleus to start the fermentation process.

b. Cellular respiration simply stops at the lactate mid-product and does not proceed any further.

c. The backlog of ADP causes the pyruvate to produce ATP directly.

d. There is more pyruvate than the preparation reaction can oxidize; this uses NADH and regenerates NAD+ which pick up more electrons and keep glycolysis operating.

e. Pyruvate is always reduced to lactate but this is the only process left when oxygen is not available.

Answer 1

D). There is more pyruvate than the preparation reaction can oxidize; this uses NADH and regenerates NAD+ which pick up more electrons and keep glycolysis operating.