What functions do parts of the heart do?

The concept of keystone species is controversial among ecologists because most organisms are highly interdependent. if each of the trophic levels is dependant on all others how can we say one is most important

What condition is kept close to its set point in osmoregulation? a. body temperature b.platelet count c.blood glucose level d.water balance

Veins have a much lower blood pressure than arteries. which of these prevents backflow of blood in veins? a. pressure applied by the heart b. one–way valves in veins c. thin muscular walls of veins