Final answer:
The two main bulk flow processes in plant fluid transport are transpiration, driven by the cohesion-tension theory, and guttation, explained by the pressure flow hypothesis.
Step-by-step explanation:
The two main bulk flow processes that transport fluids in a plant are transpiration and guttation. These processes involve the movement of water and solutes within the vascular system of plants. Transpiration is the process where water is absorbed by the roots and then moves through the xylem vessels up to the leaves, where it evaporates from the stomata. This loss of water vapor creates a negative pressure in the xylem that helps pull water upward from the roots, a mechanism described by the cohesion-tension theory.
Guttation, on the other hand, is the exudation of droplets of xylem sap on the tips or edges of leaves of some vascular plants, like grass and small herbs, when root pressure becomes high, usually at night. This process is driven by positive root pressure forcing water through the vascular system to the edges of the leaves, a phenomenon that is explained by the pressure flow hypothesis.
The Pressure flow hypothesis explains how sugars (sap) move from the source (areas of high sugar concentration, like leaves) to the sinks (areas of low sugar concentration, like roots, fruits, and storage organs) in the phloem. According to this hypothesis, sugars are actively transported into the phloem at the source and this creates a high pressure that drives the movement of sap towards the sinks.