Glycolysis is the first phase of aerobic cellular respiration. It is a complex, enzyme controlled set of reactions in which glucose molecules are broken down into pyruvate in the absence of oxygen. Although it does not produce much ATP, glycolysis is important because pyruvate is the raw material for the next phase of cellular respiration, which will ultimately produce large amounts of ATP by oxidative phosphorylation. One of the enzymes at the beginning of glycolysis is PFK, phosphofructokinase, an allosteric enzyme. When ATP binds to the allosteric site on PFK, the enzyme changes shape and no longer functions. Which of the following statements best explains the importance of the enzyme PFK in glycolysis?
a. PFK inhibits glycolysis when oxygen levels are high
b. PFK enables glycolysis to continue when no oxygen is present
c. PFK inhibits the production of ATP when ATP levels are high
d. PFK enhances the production of ATP when ATP levels are high