For plant physiology lab Pressure bomb mass and bubble potom

For plant physiology lab- Pressure bomb, mass and bubble potometer.

a. If Plant A exhibits greater water tension than Plant B as measured by a pressure bomb, which plant has the more negative leaf water potential, and how could you tell?

b. Imagine if, after setting up your potometer you used a blowtorch to seal the end of the pipette trapping the air bubble inside . During transpiration. what would you expect to observe in the sealed pipette over time, and how could such a setup be used to estimate the actual tension and therefore water potential of the plant in MPa?

Solution

(a)Pure water has maximum water potential as solutes are added free energy is reduced flow of solution slows down this means the solution now has more negative water potential.

Since PlantA has greater water tension it has less negative water potential than PlantB so we can say PlantB has more negative water potential than PlantA therefore movement of water takes place from PlantA to PlantB .

(b)As water evaporates more water is drawn into xylem that are exposed at the cut end of stem.Air bubble introduced in capillary tube,as the distance bubble travel shows how much water the stem taken up.Faster the rate of transpiration faster the bubble moves. Sealing the pipette will create difference in rate of transpiration this also create difference in actual tension and water potential .Analyzing initial value and value after sealing pipette value of actual tension and water potential can be calculated in MPa.