Leeches are parasitic because they suck blood not giving any benifit but harm.
Answer:
I would have to say recharge of the aquifer by using ground water after some precipitation.
Explanation:
Melting snow or rain increases ground water that percolates down to replenish the aquifer.
Elevation changes causes the aquifer to flow up in low spots/springs on the surface. And the cycle repeats through evaporation and plant respiration.
Answer: Contractility of the left ventricle myocardium ensures that blood will have enough force to reach the rest of the body.
Explanation: Frank Starling Law....Cardiac output=heart rate x stroke volume.
Concerning your heart, that's the circulatory system
Your lungs are the respritaory system