Explain the significance of what Loewi observed in his experiment with the two frog hearts.
A. It suggests that all vertebrate hearts receive both inhibitory and excitatory signals from different nerves.
B. It showed that nerves have a direct electrical effect on heart muscle.
C. It showed that neurons communicate with muscle by electrical signals.
D. It suggests that a chemical substance released from the first heart, when added to the second heart, reproduced the effects of electrical stimulation.
Answer: D
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The first major split in evolution separated
a. all three lineages from each other. b. Archaea from bacteria and eukaryote ancestors. c. Bacteria from Archaea and eukaryote ancestors. d. eukaryote ancestors from Archaea and Bacteria. e. none of these.
The accompanying figure shows that the rate of alarm calls made by black-tailed prairie dogs is dependent on a perceived threat by a predator. This behavior affects ________
A) the direct fitness of the caller B) the indirect fitness of the caller C) both the direct and indirect fitness of the caller D) neither the direct nor indirect fitness of the caller