The heart’s internal pacemaker beats by:
an internal implant that sends an electrical impulse through the heart
the excitation of cardiac muscle cells at the sinoatrial node followed by the atrioventricular node
the excitation of cardiac muscle cells at the atrioventricular node followed by the sinoatrial node
the action of the sinus

The sketch shows a rynchosaur, an extinct animal that is known only from fossils. there has been much debate about the classification of these creatures. some scientists suggest that they belong with primitive amphibians, and some think they are related to snakes and lizards.the data equally support both cases. which statement best explains how to draw a cladogram that includes the rynchosaur? draw the cladogram for amphibians. draw the cladogram for reptiles. draw two cladograms, both showing the traits, and leave it as a hypothesis. draw two cladograms, both showing the traits, and have scientists vote

Explain the significance of the increased cell specialization of the volvocine line

What process occurs during cellular development as the cell changes into a specific type of cell with specialized functions? a. binary fission b. fusion c. differentiation d. meiosis