The Transpiration Lab

             In this lab, you will be dealing with water potential and how it affects the movement of water within plants. You will measure transpiration under different conditions and study the organization of the plant stem and leaf by observing sections of tissue.


             The main objectives of this lab deal with transpiration and the processes involved for transpiration. You have to know how water moves from roots to leaves (including physical and chemical properties of water) and the forces created by different means of water potential and transpiration. You will learn how changes in the environment affect the rate of transpiration and (through observing) the functions of the parts previously recognized in dissection. .


             The amount of water a plant needs is closely related to the rate of transpiration which the plant experiences. Several internal and external processes dictate the transportation of water through the plant everywhere for roots to leaves; osmosis, root pressure, and transpiration are the main influencing factors of water transportation. Water potential, also, plays a major role in the transportation of water and is influenced by several factors; factors which include solute concentration and pressure. .


             Use a potometer for this experiment; you are going to place the tip of a pipette into a 16 in. tube of plastic tubing and run water through the tubing until all of the air bubbles are gone. Carefully cut the plant stem under water, careful not to get any air into the xylem, and insert the freshly cut stem into the open end of the tubing. Use petroleum jelly to seal the area around the stem. Let the potometer equilibrate for 10 minutes and then, with the lights on and a fan blowing directly on it, record the initial value of water in the pipette and record the rate of transpiration every 3 minutes for 30 minutes. At the end of the experiment cut off all of the leaves, blot them, and record their mass in table 9.

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