B) Steroid hormones can act in very small concentrations and very few molecules of steroids
need to cross the lipid bilayer.
C) Steroid hormones act on cells close to where they were produced and very few molecules are
required to travel such a short distance to cross the lipid bilayer.
D) Steroid hormones act on the same cells in which they are produced and, therefore, are within
the cell they are acting upon.
22) Tadpoles must undergo a major metamorphosis to become frogs. This change includes
reabsorption of the tail, growth of limbs, calcification of the skeleton, increase in rhodopsin in
the eye, development of lungs, change in hemoglobin structure, and reformation of the gut from
the long gut of an herbivore to the short gut of a carnivore. Amazingly, all of these changes are
induced by thyroxine. What is the most likely explanation for such a wide array of effects of
thyroxine?
A) There are many different forms of thyroxine, each specific to a different tissue.
B) Different tissues have thyroxine receptors that activate different signal transduction pathways.
C) Some tissues have membrane receptors for thyroxine, while other tissues have thyroxine
receptors within the nucleus.
D) Different releasing hormones release thyroxine to different tissues.
23) When adenylyl cyclase is activated ________.
A) cAMP is created
B) cAMP is destroyed
C) G proteins bind to cAMP
D) steroid hormones pass through the lipid bilayer
24) Insect hormones and their receptors _____.
A) act independently of each other
B) are a focus in pest control research
C) utilize cell-surface receptors only
D) are active independently of environmental cues