Explain why the signal molecules used in neuronal signaling work at a longer range than those used in contact-dependent signaling
What will be an ideal response?
The neurotransmitter released from a neuron in neuronal signaling must diffuse across the synaptic cleft to reach receptors on the target cell. In contrast, in contact-dependent signaling, the signal molecule is attached to the plasma membrane of the signaling cell and interacts with receptors located on the plasma membrane of the receiving cell; thus, the cells must be in direct contact for this type of signaling to occur.
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The water vascular system of echinoderms _____
A) functions as a circulatory system that distributes nutrients to body cells B) functions in locomotion and feeding C) is bilateral in organization, even though the adult animal is not bilaterally symmetrical D) moves water through the animal's body during suspension feeding E) is analogous to the gastrovascular cavity of flatworms
The trp operon is ____ unless tryptophan is ____
a. turned on; available in the environment b. turned on; bound to the operator c. turned off; bound to the repressor d. turned off; bound to the promoter e. turned on; synthesized by the trp repressor gene
A lens
a. is the amount that an object's image is enlarged. b. is the extent to which detail in an image is preserved during the magnifying process. c. is the degree to which image details stand out against their background. d. focuses light rays emanating from an object to produce an image.
The four most common elements in living organisms are
A) C, H, O, Fe. B) C, H, O, Na. C) C, H, O, N. D) C, N, O, Na.