Though I do not believe that a plant will spring   up where no seed has been, I have great faith in a   seed. Convince me that you have a seed there and I   am prepared to expect wonders.              ----Henry David Thoreau   by David L. Brock,          Jewel J. Reuter, &          Pamela S. Duncan

•  A common problem teachers confront when studying plant development is making this often unfamiliar material readily accessible to students.  The traditional approach comparing tissue and organ morphology usually lapses into a simple textbook analysis; while a real investigation of the biochemistry of development involves equipment few schools can afford.  The model experimental protocol presented here is designed to equip teachers to present plant development in a hands-on fashion that engages students' minds and provides for a wide range of supplemental, quantitative investigations.  It employs testing rates of cellular respiration to demonstrate the relationship between the metabolic rates of different parts of the developing plant and their respective roles, and it can be performed in any classroom using common lab equipment at relatively little cost.

Conceptual Objectives:

• Students will learn about the major stages of plant development in terms of both their morphology and physiology.
• Students will study the evolutionary history of plants by comparing their developmental processes.
• Students will hypothesize reasons for differences in metabolic rates based on structure, function, or developmental stage of  the plant
• Students will relate respiration rate to differentiation and development.

• Students will engage in experimental problem solving, creating hypotheses, designing protocols, and collecting and analysing data.
• Students will measure the change in gas pressure or volume due to the uptake of oxygen in a closed system and interpret the causes for the change.
• Students will discover how to relate the concept of slope to the metabolic rate.
• Students will use calculator or computer based technology to solve a problem.
• Students will describe function of respirometers in terms of the ideal gas law.
• Students will test various plant structures to compare developmental levels.

• biology students (AP, honors, general)
• 9-12
• traditional lab exercise recommended for those unfamiliar with the material or who have little time in the curriculum to spend on plant development

Notes to the Teacher: to top

    The protocol for this activity uses the analysis of cell respiration in different key organs of germinating and sprouting seeds to demonstrate the relationship between each organ's metabolic rates and its respective role in development.  Since energy production is greatest in those parts of the plant where differentiation and growth are occurring the most, comparing the respiration rates from these locations allows one to study the development and growth events in the early life cycle of plants and, hence, to know what is occurring and where.  This information in turn provides an empirical foundation for discussing why the different differentiation events occur when they do.
    The experimental system for this model is an elementary one, employing  the fact that in self-contained systems there is a measurable change in gas volume and pressure if the amount of gas or a portion of that gas is removed.  Normally, any carbon dioxide release in such a situation by a living organism would basically replace the oxygen being consumed, maintaining a constant volume and pressure.  But when the carbon dioxide is removed from the surrounding air, one creates a condition where any oxygen respired causes a corresponding drop in both the volume and the pressure of the contained gas.  These respective drops, in turn, are easily quantified using simple respirometers utilizing either traditional water displacement methods or gas probes interfaced with a calculator.

For additional information:

• on the experimental set-up
• on applications of the model
• on related issues and concerns
• on background information on plant development

A. Per Group of 2-4 Students
        3 125-ml respirometers (see experimental protocol)
        3 600-ml beakers
        1 100-ml graduated cylinder
        1 250-ml graduated cylinder
        1 thermometer
        glass beads
        marker
        eyedropper
        weigh boats
        forceps or tweezers
        either:
            TI-82 or TI-83 calculator with CBL unit
            Vernier Bio-Software Package or equivalent
            Vernier Biology Gas Pressure Sensor (0-10 kpasc) or equivalent
         or:
            water-displacement apparatus

B. Per Classroom of 24
        balances
        absorbent cotton
        non-absorbent cotton
        1-L 15% KOH
        an assortment of germinating seeds:
                kidney beans
                great northern beans
                alaskan snow peas
                corn
 
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For information on:

• a discovery-approach student lab
• a traditional student lab
• alternative applications & experiments

• on pre-lab questions
• on post-lab questions (AP or honors)
• on post-lab questions (general)

    Plants are not the only organisms to which a teacher can apply the model experimental protocol presented here.  Classes could study invertebrate metamorphosis with this technique, comparing how respiration rates change from one developmental form to another (the common flour beetle is one such example).  They could also study more than one species of insects to compare respiration rates in order to examine evolutionary relationships.  The growth of molds on food could be analysed to determine optimal conditions for their development without having to wait for extended periods of time, and potentially, even certain vertebrates could be studied with this system.  Basically anything which respires could technically be use with the model, and the only current limitations are that the organisms studied must be terrestrial (the authors are working on an aquatic system using dissolved oxygen probes, but it has not yet been thoroughly field-tested).
    Teachers are encouraged to think up an idea and try it.  If it works, drop one of the authors a line at their e-mail address and let them know.  It is the hope that this lesson will be continue to develop itself and tested material to add this web site is greatly welcome.

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Bibliography

• Bewley, J. and Black, M.  Seeds: Physiology of Development and Germination, 2nd ed.     New York: Plenum Press, 1994.
• Botha, F., Potegieter, G., and Botha, A.  "Respiratory Metabolism and Gene Expression During Seed Germination."  Plant Growth Regulation (11), 1992.
• Come, D. and Carbineau, F.  "Some Aspects of Metabolic Regulation of Seed Germination and Dormancy."  Recent Advances in the Development and Germination of Seeds.  New York:  Plenum Press, 1989.
• Deltour, R. and De Barsy, T.  "Nucleolar Activation and Vacuolation in Embryo Radicle Cells During Early Germination."  Journal of Cell Science (76:67-83), 1985.
• Hopkins, W.  Introduction to Plant Physiology.  New York:  John Wiley and Sons, 1995.
• Palme, K. and Schell, J.  "On Plant Growth Regulators and Their Metabolism:  A Changing Perspective."  Seminars in Cell Biology (4:2), 1993.

• Missouri Botanical Garden
• Plant Metabolic Network
• Scott's Botanical Links
• Seeds of Life
• Texas Instruments (CBL)
• Vernier Software