Which component of the heart's conduction system is considered to be the heart's pacemaker?

Is a hamster and guinea pig part of the same species ?

The influenza virus cause the flu, but not other diseases. why?

What is true of all organisms in the kingdoms protista, plantae, fungi, and animalia? a. they are multi-celled. b. they are photosynthetic. c. they have cells that contain membrane-bound organelles. d. they contain cells that lack membrane-bound organelles.