Which observation suggested to sutherland the involvement of a second messenger in epinephrine’s effect on liver cells?
a. enzymatic activity was proportional to the amount of calcium added to a cell-free extract.
b. receptor studies indicated that epinephrine was a ligand.
c. glycogen breakdown was observed only when epinephrine was administered to intact cells.
d. glycogen breakdown was observed when epinephrine and glycogen phosphorylase were combined.

Which of the following observation darwin shape his concept of descent with modification? a) species diversity declines farther from the equator. b) fewer species live on islands than on the nearest continents. c) birds live on islands located farther from the mainland than the bird's maximum nonstop flight distance. d) south american temperate plants are more similar to the tropical plants of south america than to the temperate plants of europe. e) earthquakes reshape life by causing mass extinctions.