Please help me fill out the blanks

Which part of a feedback mechanism is able to monitor the conditions outside of cells and usually uses nerve cells to relay this information to an intergrating center

Select all of the statements which are true. electrons are located in shells or orbits around the atom. electrons orbit slowly around the atom. electrons travel in one flat path around the nucleus of an atom. the valence of an atom is determined by the number of electrons in the atom's outermost shell.

How does blood clotting prevent the entry of pathogens through cuts and wounds? answer asap,, this is due tomorrow. will mark as brainliest or whatever you call it : )