Plant Physiology

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.

capillary action
cohesion
tension
tensile strength
cavitation

Sequence Question: Number 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.

Root Pressure
Capillary Action
Barometric Pressure Hypothesis (extra credit)
Compensating Pressure Hypothesis (extra credit)

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

1.

2.

3.

4.

5.

Calculation Questions: (show your work)

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

What is Poiseuille's Law?
Explain why conifers (gymnosperms) are more common in the boreal forest biome? (Hint: think xylem cell type)
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)