Biochemicals produced in a gland that travel through the blood stream and alter the metabolism of specific target cells are
A. enzymes.
B. pheromones.
C. neurotransmitters.
D. hormones.
E. pectines.
Answer: D. hormones.
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The function of mechanical digestion is to break down large chunks of food into smaller pieces. Why is this important? Smaller pieces of food _____
A) do not taste as good as larger pieces of food B) have more surface area for chemical digestion than do larger pieces of food C) are easier to excrete than are larger pieces of food D) are more easily stored in the stomach than are larger pieces of food
During the S period of interphase
(a) cell growth takes place. (b) nothing occurs because this is a resting period. (c) chromosomes divide. (d) synthesis (or replication) of the nucleoproteins takes place.
Mutations in structural genes account for almost all of the differences that we observe among different species
A. true B. false
Tracheids differ from vessels in that _________
A. they lack end-walls B. they lack pits C. they are formed from a single cell D. water enters and exits through pits