Answer:
while the heart beats
Explanation:
Blood pressure of the heart is the pressure by which heart pumps blood through the arteries. Since the blood flow through the heart and arteries is pulsatile, there are two heart blood pressures: systolic and diastolic blood pressure. Normal systolic pressure is about 120 mmHg.
Diastolic blood pressure is the pressure of the blood between heartbeats (when heart is not active, relaxed). Normal diastolic blood pressure is about 80 mmHg.
The answer is that the criteria of classification change whith the improved understanding of organisms around us
Not sure about the answer but I think its the size of the system