Spring.wmf (18300 bytes) Plant Physiology (Biology 327)  - Dr. Stephen G. Saupe;  College of St. Benedict/ St. John's University;  Biology Department; Collegeville, MN  56321; (320) 363 - 2782; (320) 363 - 3202, fax;    ssaupe@csbsju.edu

Water Transport Questions

 Define Use a complete sentence(s) to define each of the following.

  1. capillary action

  2. cohesion

  3. tension

  4. tensile strength

  5. cavitation

Sequence QuestionNumber the following tissues in sequence from the one with the highest water potential (least negative = 1) to the lowest (most negative = 9) water potential.

  air (50% RH)   soil (saturated)
  endodermis   cortex
  pericycle   palisade cell
  root xylem   root hair
  leaf xylem    

Xylem Cell Question
Use the following list of xylem cells to answer the following questions. 

a.  fibers c.  vessels e.  all of the above
b.  parenchyma cells d.  tracheids f.  none of the above
1.    cells primarily for support
2.   water transport cell with the largest diameter
3.   water transport cells that are stacked end-to-end
4.   cells that move water from inside the stem to the outside and vice versa; part of the rays
5.   alive at maturity
6.   found in the xylem
7.   found in wood
8.   occur in the phloem
9.   cells that can store starch
10.   cells that have mitochondria and other organelles
11.   water transport cells that are cigar-shaped
12.   water transport cells that overlap; extensive pits in the wall

Hypothesis Evaluation
For each of the following hypotheses to explain water transport, give at least one reason why it is considered to be FALSE.

  1.  Root Pressure

  2. Capillary Action

  3. Barometric Pressure Hypothesis (extra credit)

  4. Compensating Pressure Hypothesis (extra credit)

Cohesion-Tension: Hypothesis Evaluation
Provide at least FIVE lines of evidence that support this hypothesis






Calculation Questions:  (show your  work)

  1. Calculate the height that a column of water can move up a capillary tube that is 25 �m in diameter.


  2. Consider a tree that is 50 meters tall.  Calculate the pressure (MPa) required to move water to top of this tree if the flow rate is 10 cm sec-1 and a typical xylem cell is 100 �m in diameter.


Short Answer Questions:

  1. What is Poiseuille's Law?


  2. Explain why conifers (gymnosperms) are more common in the boreal forest biome? (Hint:  think xylem cell type)


  3. Based on your knowledge of the cohesion-tension theory, explain why plant height is limited by the ability of water to reach the tips of tall trees.  (Hint: cavitation)


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Last updated:  02/24/2009     � Copyright  by SG Saupe