Describe the route taken by water from the soil up to the evaporating surface of a plant.

• Water is drawn into the root hair cells by osmosis; 
• Due to the presence of dissolved substances in the cell sap of root hairs, the concentration of cell sap is greater than that of the surrounding solution in the soil/concentration gradient; 
• This exerts a higher osmotic pressure, thus drawing the water molecules across the cell wall and cell membrane into the root hair cells; 
• More water drawn into the root hair cells dilutes the cell sap; making it less concentrated than that in the adjacent cortex cell of the root; 
• Due to this osmotic gradient, water moves from the adjacent cells to the next and to  the next  by osmosis; until it enters the xylem vessels located in the center of the root; 
• The xylem vessels of the root then conduct the water up into the xylem vessels in the stem into the leaves; 
• Root pressure pushes water up the stem; this force can be considerably high in some plants; energy from the endodermal cells of the root is responsible for driving this force; 
• In the xylem vessels, water would rise up by capillarity; 
• To some extent because the vessels are narrower and there is a high attractive force between the water molecules themselves; the cohesive force; and between water moleculess and the cell walls; the adhesive force; which are important in the maintenance of a continuous and uninterrupted water column in the xylem vessels up the tree to the leaves; 
• Water vaporizes from the spongy mesophyll cells; their cell sap becomes concentrated than the adjacent cells. This increases the osmotic pressure of the spongy mesophyll cells; as a result of this, water flows into the cell from other surrounding cell, which in turn takes in water from xylem vessels within the leaf veins; this creates a pull/suction force that pulls a stream of water from xylem vessels in the stem and roots. This force, known as transpiration pull; It  maintains a continuous column of water from the roots to the leaves; 
• Water flows from the midrib into leaf veins from where it enters leaf cells; from the mesophyll cells, it enters the airspaces; then the substomatal air chambers; from where it evaporates through the stomata; to the atmosphere; 

 Max. 20 mks