Why are intercalated discs essential to the function of cardiac muscle?
the discs maintain the barriers between the cells.
the discs pass nutrients between cells.
the discs ensure that all the cardiac muscle cells beat as a single unit.
the discs control the heart rate.

Which statement describes how favorable traits in a population relate to natural selection? they are the only traits that ever exist in the population. they build in the population over time. they are rarely passed on to offspring. they are found only in a few individuals within the population.