Re: Do trees have a 'hearbeat' measured by the rate sap runs up and down? AND

No, trees do not have a heartbeat because they have no heart or pump. The 
driving force for water movement upward in the tree trunk is the evaporation 
of water from the leaves. The water is literally pulled up the trunk because 
the thin water columns in the narrow diameter tubes, called xylem, are held 
together tightly by the strong attraction of water molecules to each other. 

Root cell membranes prevent dissolved mineral nutrients, or ions, from being 
sucked into the cells. However, roots can "suck in" mineral nutrients into the 
intercellular spaces of the roots outside the vascular cylinder in the center 
of the root. Most mineral nutrients are actively tranported across the cell 
membrane or plasma membrane. That enables the root to be selective in what 
ions it absorbs and also prevents the absorbed ions from leaking back out of 
the cells.

References


Re: I need information on the circulatory (vascular) system of plants


Re: Xylem vs. phloem transport directions


Transport of Water and Minerals in Plants