A(n) __________ is an extracellular signaling molecule that exerts its effect at very low concentrations
Fill in the blank(s) with the appropriate word(s).
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When dealing with stable isotopes, enzymes tend to favor
A) the lighter isotope. B) the heavier isotope. C) the isotopes in about equal proportions. D) either the lighter or the heavier isotope, depending on environmental conditions.
The bone in the upper arm is the:
a. radius b. ulna c. tibia d. humerus e. femur
Glial cells perform all of the following functions EXCEPT ____
a. nourish neurons b. control the concentrations of electrolytes c. protect and support neurons d. produce action potentials e. insulate axons
The major function of the protonephridia in the flatworm is to:
a. conserve water. b. conserve salts. c. eliminate waste materials such as ammonia and urea. d. eliminate excess water. e. regulate the pH of the gastrovascular cavity.