43. Which second messenger is most directly responsible for mediating glucagon’s intracellular effects? (A) Ca²⁺ (B) cAMP (C) IP₃ (D) DAG

48. Which statement best explains why pentose phosphate pathway activity increases during oxidative stress? (A) NADPH directly activates ribose‑5‑phosphate synthesis (B) NADP⁺ accumulation activates glucose‑6‑phosphate dehydrogenase (C) ATP depletion stimulates the oxidative phase (D) Glutathione directly activates transketolase