Correct and appropriate signal transduction processes are generally under strong selective pressure and are determined by the properties of the molecules involved, the concentrations of signal and receptor molecules, and the binding affinities
between signal and receptor. Therefore, a hormone action is very specific in a species at any one point in time. However, there are examples of very diverse functions of a specific hormone between groups of organisms. For example, thyroxin, which is produced in all vertebrates and many invertebrates, can trigger growth, differentiation, metamorphosis, maturation, reproduction, behavior, temperature tolerance, osmoregulation, or seasonal adaptation depending on the organism in which it is produced. What is the most logical explanation for such different responses triggered by thyroxin in organisms? A) The concentration of thyroxin varies in different organisms. Invertebrate organisms do not have as much thyroxin as vertebrate organisms.
B) Thyroxin and its receptor molecules have a different binding affinity in different organisms.
C) Receptor molecules for thyroxin are located on different tissues in different organisms.
D) The structure of thyroxin is substantially different in different organisms.
D
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You are trying to determine if honeybees have social immunity to nosema, an economically devastating parasite that attacks adult honeybees. You mark some honeybees with a spot of red dye and expose them to a solution containing a sublethal dose of the parasites. Another set of honeybees is exposed to the same solution without parasites. After this exposure, you mix some of the unmarked bees with
the marked bees (Mixed Group). The rest of the unmarked bees are not mixed with other bees (Unmixed Group). When you expose both the Mixed and Unmixed groups of bees to a lethal dose of the parasite, all the bees die. What might you conclude from this experiment? A. The marked honeybees exposed the unmarked bees to a lethal dose of the parasite. B. There is no social immunity for nosema in honeybees. C. There is social immunity, but only at a sublethal dose. D. There is no social immunity, but there is humoral immunity. E. There is both social and nonspecific immunity for nosema in honeybees.
Most microbes that inhabit estuaries are ________.
A. halovariable B. halophobic C. halophilic D. halotolerant
Three molecules that easily diffuse through the plasma membrane are oxygen, carbon dioxide, and urea.
a. true b. false
Which of the following best describes the structure of DNA?
A. single helix B. protein coil C. double helix D. globular RNA