What structure releases the chemical cues that help guide a developing pollen tube toward an ovule?
a. the egg
b. the central cell
c. the antipodal cell
d. the synergid
Ans: d. the synergid
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If the age structure of a country's population is balanced, what prediction can be made about the near future?
A. The birth rate will decline. B. The death rate will decline. C. The population will not increase rapidly. D. The population will increase rapidly. E. The demographic transition will begin.
Substance C is secreted from a neuron, and binds to its receptor on a nearby cell, triggering an increase in intracellular
cAMP. Substance C is therefore a ligand for a ____.
a. a receptor tyrosine kinase b. a G-protein-coupled receptor c. a hormone receptor d. a ligand-gated ion channel e. guanylyl cyclase
Water is an example of a(n)
a. atom. b. ion. c. compound. d. mixture. e. element.
The random movement of molecules from areas of high concentration to low concentration is referred to as:
a) osmosis. b) transport. c) diffusion. d) All of these choices are correct.