16. What is the name of the protein signaling molecule that alters glucose uptake, and where would its receptors be located?

A. Insulin; many different cell types that use glucose for fuel
B. Insulin; beta cells of the pancreas
C. PDGF; the blood
D. NGF; the nerves involved in simple reflexes

17. In the signal transduction mechanism known as protein phosphorylation

A. the signaling molecule binds to a surface receptor
B. receptor kinases play a key role in triggering the signal cascade
C. phosphorylated proteins act with enzymes to trigger the signal cascade
D. All of the above

18. Cell signaling can be classified into

A. three distinct types based on the distance over which the signaling molecules act
B. two distinct types based on the distance over which the signaling molecules act
C. three distinct types based on the signaling molecules
D. none of the above

19. Which of the following statement is correct?

A. Cell communicate with one another in multicellular organisms using extracellular signaling molecules or hormones
B. Cell communicate with one another in unicellular organisms using extracellular signaling antigen and antibody
C. Cell communicate with one another in multicellular organisms using intracellular signaling molecules only
D. Cell communicate with one another in unicellular organisms using intracellular signaling antigen and antibody

20. In vasodilation, proper nerve signals sent to blood vessels cause

A. the release of nitric oxide from endothelial cells
B. relaxation of smooth muscle cells
C. reduced blood pressure
D. All of the above