Thyroxine Can Trigger Growth, Temperature Tolerance, or Osmoregulation Depending on the Organism

Multiple Choice

Thyroxine can trigger growth, temperature tolerance, or osmoregulation depending on the organism in which it is produced. Which is the most likely mechanism for such diverse responses in different organisms?

A) The concentration of thyroxine varies in different organisms. Invertebrate organisms do not have as much thyroxine as vertebrate organisms.
B) Thyroxine and its receptor molecules have different binding affinities in different organisms.
C) Receptor molecules for thyroxine are located on different tissues in different organisms.
D) The function of thyroxine in a particular tissue is determined by the genes that are transcribed by the activated thyroxine receptor.