Write a one-sentence explanation for each of the following statements.
(a) In liver, glucagon stimulates glycogen breakdown via cAMP. Although you might expect glucagon to stimulate catabolism of the glucose formed as well, glucagon inhibits glycolysis and stimulates gluconeogenesis in liver.
(b) An individual with a glucose-6-phosphatase deficiency suffers from chronic hypoglycemia.
(c) The action of phosphorylase kinase simultaneously activates glycogen breakdown and inhibits glycogen synthesis.
(d) The presence in liver of glucose-6-phosphatase is essential to the function of the liver in synthesizing glucose for use by other tissues.