While snorkeling, a student observes an active marine animal that has a series of muscular tentacles bearing suction cups associated with its head. Segmentation is not observed, but a pair of large, well-developed eyes is evident. The student is observing an animal belonging to which class? Question 21 options:

A. sponge

B. mollusk

C. arthropod

D. echinoderm

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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phaneritic textures in which phaner means visible so phaneritic textures are standard of impertinent volcanic rocks. these rocks crystallized gradually under the surface of earth. when the magma cools deliberately then the ores have chance to develop and produce long crystals.

d. cellulose and starch