Water Relations of the Whole Plant
Goals and Objectives
 

1. Explain the process of transpiration and the role of vapor pressure differences in controlling the movement of water between plant leaves ana the atmosphere.
2. Be able to discuss how environmental factors regulate the rate of transpirational water loss from a plant.
3. Be able to describe the anatomy of the water-conducting system in plants.
4. Be able to explain how the anatomy of the vascular system in plants is involved with maintaining a column of water in tall trees.
5. Be able to describe how water from the soil is taken up by plant roots.

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Water Relations of the Whole Plant
Goals and Objectives
 

1. Give a definition of transpiration.
2. Draw a cross section view of a plant (Dicot) leaf.  Label the following structures:  cuticle, upper and lower epidermis, palisade mesophyll, spongy mesophyll, vascular bundle, air space (and the substomatal air space), stoma, guard cells, stomatal apparatus.
3. For each of the structures listed above in question #2, give a definition and describe the function of the structure.
4. How is the cuticle involved in water lose by transpiration?
5. What are the two stages of the transpiration process?
6. From where does the majority of water in a leaf evaporate?
7. Explain the difference between stomatal and cuticular transpiration.  Which of the two is more important in water lose from a plant?
8. Give some examples of how cuticular transpiration can vary in regard to leaf anatomy.
9. What is the driving force for transpiration?
10. What occurs to the liquid water in the leaf air spaces?
11. Define these three terms and explain how these three terms are related:  vapor density, vapor pressure, saturation vapor pressure.
12. What does Raoult's law describe?  What are the components that make up the equation for Raoult's law and what do they tell us about vapor pressure?
13. What affect does solute concentration have on vapor pressure?  What affect does temperature have on vapor pressure?  How does this affect the movement of water from the leaf to the atmosphere?
14. Describe how humidity, temperature, and wind speed affect transpiration.
15. In chapter one you looked briefly at the water and photosynthate conducting tissues of a plant (i.e. the xylem and phloem respectively).  Take some time now to make a list of the different xylem cells and their characteristics.
16. Illustrate the structure of a bordered pit pair.  How does this structure control the movement of water and air in the xylem cells?  Why is this important? (NOTE:  If you are answering these question as you read the chapter, you should be on page 45 of the text.  The answer to the last part of this question (Why...?) can be found on pages 52 and 53 - so make sure  you come back to finish this question later.)
17. In an evolutionary sense vessel elements are more advanced than tracheids.  How did Poiseuille's equation help show that vessels could "move" more water than tracheids?
18. Describe how root pressure is developed in a plant and indicate how important root pressure is to the assent of water from the soil to the leaves of a plant.
19. Describe how capillary action occurs in a plant and indicate how important capillary action is to the movement of water in a plant.
20. Describe the cohesion theory of water movement in the plant.  (NOTE:  in lecture I will talk about the cohesion-adhesion-tension theory; these are the same thing.)
21. Movement of water through a plant is driven by transpiration and maintained by the cohesion-adhesion-tension of the water column.  In order for movement of water to occur, the water column in a plant must not be broken.  Answer these series of questions to find out how plants maintain their water columns.
• What is tensile strength?
• What is the range of water tension in the xylem for temperate deciduous trees?
• What is meant by a metastable state?
• If water under tension in xylem is in a metastable stare, how is stability of the water column achieved?
• What is cavitation?  Why does it occur in xylem?
• What is an embolism?  What does it do to the water column in the xylem ?
• Going back to question #16, describe how the structure of vessels and tracheids help in entrapment of embolism.
• give some example of how embolisms are removed from the water column.
22. What portion of the root absorbs the most water?  What adaptation is responsible for increasing surface area and allowing increased water uptake by the plant root.
23. Illustrate the cross section of a Dicot plant root.  How does the internal structure of the root aid in absorption of water?