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STUDENT OBJECTIVE

Students observe the structure of roots and stems to learn the differences between monocots and dicots. Primary and secondary growth are discussed. They see that water rises through xylem by transpiration, and that guard cells open and close stomata.

EQUIPMENT	AMOUNT
	(Class of 24 with 8 groups)
Compound microscope Dissecting microscope	1/student 1/student
MATERIALS
Living plants Fibrous root system (grass) Taproot system (carrot, dandelion, etc.) Adventitious root system (corn) (If above not available, order Root Type Kit—CBS#PB 680A) Rooting Onion Sets Celery with leaves Tomato, Coleus, or geranium plant Leaves for guard cell investigation (spiderwort or Zebrina) Preserved specimens Woody twigs (hickory, buckeye, other) with apical bud (CBS#PB 700)* or Woody Stem Comparison Kit (CBS#PB 704A)* Prepared slides (can be shared to reduce costs) Ranunculus (buttercup) root tip, longitudinal section Ranunculus root, cross section (CBS#30-2090)* Corn root, cross section (CBS#30-2300)* Coleus shoot tip, longitudinal section Herbaceous dicot stem, cross section Tilia (basswood) stem, 2-yr, cross section Quercus (oak) stem combination cross section, tangential section, and radial section (CBS#30-3044)* Corn stem, cross section (CBS#30-3296)* Lens paper, 2" x 4" (cut from standard package) Blotting tissue Petri dishes Filter paper, 9 cm Slides Coverslips, #1 small, square glass Beakers, 100 ml Razor blades Forceps Rubber tubing Pipettes, 0.2 x 0.005 ml Pan, 8" x 8" x 2" Light source—300 watt bulb in lamp shield	Demonstration Demonstration Demonstration 1/student 1/group 1/student 1/student 1/student 1/student 1/student Demonstration 1/student 1/student 1/student 1/student 1/student 8 pkg/lab 4 boxes/lab 4/lab 4/lab 2/student 1 box/lab 2/lab 1/student 12/lab 2 1/2 m/lab 24/lab 1/lab 1/lab

*Please refer to the Appendix for name and address of supplier.

SOLUTIONS

0.5% methylene blue
5% sodium chloride (NaCl)

PREPARATION

Two Months before Lab

1. Tomato seeds should be planted and plants cultured in a greenhouse or other acceptable environment. Obtain large geranium and Coleus plants and culture with the tomato plants.
2. The seeds to be germinated and the prepared slides should be ordered to arrive eight days prior to the lab.
3. Woody twigs can be collected and stored for use.

Week before Lab

1. Onion sets should be germinated four to six days prior to the lab in moist vermiculite.
2. Methylene blue preparation:
   0.5% methylene blue 0.5 g dye/100 ml distilled water
   Dissolve the dye by stirring constantly. Store the dye in a stoppered Erlenmeyer flask.

   Shelf life: six months

3. Sodium chloride preparation:
   5% NaCl 5 g NaCl/95 ml distilled water
   Completely dissolve the salt in water and store in eight dropper bottles.

   Shelf life: one month

4. Obtain plants with fibrous root, taproot, and adventitious root systems. Wash soil from roots and place in a beaker of water as demonstration.

CLASSROOM SUGGESTIONS

1. Slides of plant anatomy can be used to summarize the laboratory.
2. Minimum homework would be a short essay on water entrance, movement, and transpiration.
3. Check out the links for this lab topic at http://auth.mhhe.com/biosci/genbio/dolphin/ You will find useful materials for developing your lab introduction or summary, and in some cases, you may want to tell students to connect to a particular site for further information.

ANSWERS TO CRITICAL THINKING QUESTIONS

1. Several things could limit the height of trees, the most obvious being water transport to the top of the tree. Movement of water up the xylem involves transpirational pull, cohesion of water molecules exerted by their hydrogen bonds and adhesion of water molecules to the xylem walls. However, one needs to consider whether cohesion is strong enough to support a water column higher than 100 m. Tests have shown water cohesion is strong enough to support a water column 150 m high. The transpirational pull (tension) in xylem has been measured that would pull water up 200 m. Theoretically, when only considering water transport in xylem, trees could grow taller, perhaps another 50 m taller, above which height the water column may not support itself. It’s probable, though, that there are other limiting factors.
2. Favorable growing conditions during a year will be indicated by a relatively wider annual ring. As well, the relative distance between terminal bud scale scars is indicative of growing conditions at the time, i.e., a relatively short distance between scars could indicate unfavorable climatic conditions during that period of growth.

SUPPLEMENTAL MATERIALS