When a heart beats, electrical impulses the muscles. The electrical pulse cause the heart to contract and retract. When the heart muscle contract and pull inward, the heart -

Which of the following is an example of a tissue on the digestive system a. the stomach b. smooth muscle that lines the stomach c. nerve cells in the stomach d. enzyme molecules in the stomach

What statements describe a host organism?

How is ribosomal rna useful as a molecular clock? a. a large portion of the dna ring is not vital to structure or function, allowing it to accumulate neutral mutations. b. its rate of mutation increases over time as organisms continue to evolve and differentiate from each other. c. a slow mutation rate makes it useful for determining evolutionary relationships between ancient species. d. it is only found in select organisms, making it easier to compare relationships between species that have it.