What is the neuron's refractory period? O when Na* channels in the axon hillock open, allowing positive ions to enter the cell.
O a period when a neuron cannot produce another action potential because its potassium channels will not open
O a period when a neuron cannot produce another action potential because its sodium channels will not open

Awave has a wavelength of 15 mm and a frequency of 6 hertz. what is its speed?

Agene pool: a) is the collection of all the alleles found in a single species b) is the collection of all the alleles found in a single population c) is the collection of all the chromosomes found in a single population d) is the collection of genes in a species that allow the individuals to swim

Which statement describes characteristics of planarians? a they live in oceans, are parasites, and reproduce only sexually. b they live in fresh water, are parasites, and reproduce only asexually. c they live in oceans, are free living, and reproduce sexually and asexually. d they live in fresh water, are free living, and reproduce sexually and asexually.