What Turns Seeds On?

by    Erika Hunter, Poly Prep Country Day School   Brooklyn, New York  Eugene McNicholas, Kittatinny Regional High School   Newton, New Jersey  Linda Needham, Bradford High School  Kenosha, Wisconsin  Galina Pavlova, Clara Barton High School  Brooklyn, New York  Celeste Payne, Shady Side Academy  Pittsburgh, Pennsylvania

• Science Teaching Standards:
• Teaching Standard B:  The actions taken to guide and facilitate student learning
• Teaching Standard C:  The assessments made of teaching and student learning
• Teaching Standard D:  The development of environments that enable students to learn science
• Teaching Standard E:  The creation of communities of science learners
• Standards for Professional Development for Teachers of Science:
• Professional Development Standard C:  The development of the understanding and ability of lifelong learning
• Assessment in Science Education:
• Assessment Standard A:  The consistency of assessments with decisions they are designed to inform
• Assessment Standard B:  The assessment of both achievement and opportunity to learn science
• Assessment Standard C:  The match between the technical quality of the data collected and the consequences of the actions taken based on that data
• Assessment Standard D:  The fairness of assessment practices
• Science Content Standards (9-12):
• Content Standard A:  Science as Inquiry
• Content Standard C:  Life Science
• Science Education Program Standards:
• Program Standard A:  The consistency of the science program with the other standards and across grade levels
• Program Standard B:  The inclusion of all content standards in a variety of curricula that are developmentally appropriate, interesting, relevant to student's lives, organized around inquiry, and connected with other school subjects

Summary / Abstract

Instructor's Objectives

Target Age or Ability Group Audience

Teacher Instructions / Special Precautions

Materials & Equipment Needs

Background

The Student Lab

Method of Evaluation / Assessment

Extension / Reinforcement / Additional Ideas

References Including Web Addresses

National Science Education Standards (NSES) Table of Contents

The following lesson can be used as a way of approaching the scientific method during or after a unit on plant growth and development.  This investigative activity will enable students to explore the effects of specific plant hormones (abscisic acid and gibberellic acid) on seed germination.  They will formulate a hypothesis as well as design and perform the experiment to test the hypothesis.

Gibberellin and abscisic acid are two classes of plant hormones.  Gibberellin (GA₃) promotes the production of a-amylase in the seeds of many plants while abscisic acid (ABA) inhibits this production. When GA₃ concentration is equal to or greater than ABA concentration, mRNA translation of a-amylase is promoted.

Early growth of the seedling is heterotrophic.  The germinating seed once activated cannot yet make its own energy.  This is for one of two reasons:  (1) chloroplasts have not yet differentiated or (2) the rate of photosynthesis is too low to sustain growth.  This stored energy is often in the form of starch (endosperm) and must be converted into a useable form.  a-amylase converts starch into simple sugars that can be used by the developing embryo.  GA₃ plays a major role in the initiation of this conversion process.

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By the end of this activity, students will :

• gain skill in the design, implementation, and reporting of a scientific research project using the scientific method.
• understand the steps involved in seed germination.
• understand the role of plant hormones abscisic acid (ABA) and gibberellic acid (GA₃) in seed germination.
• understand the function of a-amylase, its role in starch catabolism, and the subsequent energy it produces for seed germination.

Target Audience or Age Group  to top

• Grades 9-12
• Advanced and general biology students
• Botany / Advanced Placement Biology students

• Before beginning this investigation, students should have discussed the stages of plant growth and development.  (Questions to Assess Prior Student Knowledge)
• The teacher should demonstrate how a healthy seed germinates in a damp petri dish under normal conditions several days in advance.
• Curiosity in seeds can be generated by posing questions about foods (i.e. cereal) in which students are interested.

• 1 class period for discussion of a possible procedure for investigating the effects of hormones on seed germination
• approximately 90 minutes using sterile techniques to prepare agar / starch solution and pour the plates
• 2 hours for the teacher to prepare serial dilutions
• 24 hours for seed soaking
• 1 class period to cut seeds and place on agar plates
• 30 minutes for 4 class periods for data collection  (This can be done after school.)
• 1 class period for follow-up

• Two to four students per lab group is optimum.
• Abscisic acid is light sensitive and should be stored in an opaque container.
• safety guidelines for GA₃ :
• Avoid ingestion and contact with skin.
• If there is contact, immediately rinse with soap and water.
• If there is contact with eyes, flush with water.
• Scalpel and forceps can be made sterile by dipping them into Clorox before each use.
• Students should practice safe hygiene.  (Keep hands away from body orifices.)

Materials & Equipment Needs to top

Caution:  Please label all containers and solutions ahead of time in order to avoid confusion.
 

120 monocot seeds(e.g. sweet corn Zea mays var. rugosa)	metric ruler
1% bacto-agar solution	500 mg abscisic acid (ABA)
2% soluble potato starch solution	500 mg gibberellic acid (GA3)
600 mL beaker	distilled water
four 500-mL beakers	25 mL Clorox bleach or Lysol disinfectant
10 mL graduated cylinder	95% ethanol
three 100-mL volumetric flasks	aluminum foil
three 1-L volumetric flasks	parafilm
500 mL erlenmeyer flask	scalpel or razor blade
two 1-mL disposable pipettes	forceps
forty-eight 8-cm petri dishes	analytical balance
Lugol's iodine (I2KI) solution

 

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Background to top

 
Students should be familiar with:

seed structure and function (monocot vs. dicot)

the process of catabolism

chemical regulators (hormones) of plant growth

the effects of iodine on starch

serial dilutions

 
Students need to be familiar with the following terms, which can be found in the glossary for this activity:
 

abscisic acid (ABA)	germination
agar	gibberellic acid (GA3)
amylase	hormone
catabolism	imbibition
cotyledon	monocot
dicot	seed
dormancy	seedling
embryo	starch
enzyme	testa

The following questions can be used to prompt discussion and assess student's knowledge of seed germination:

1. What is a seed?
2. What is inside a seed?
3. What is germination?
4. What are the requirements a seed needs to begin growing?
5. What role do hormones play in germination?
6. What would the world be like if seeds did not germinate?

Click here to view sample data and graph.

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The Student Lab to top

Click here for student handout.

1.  Answer the following questions:
1. Why may a seed showing proper respiration, protein and nucleic acid synthesis, and all other normal features still fail to germinate?
2. Why is plant development so much more closely linked with environmental cues than animal development is?
3. How well did the procedure work?  What changes, if any, were made during the course of the experiment?  Why were they made?
4. Which specific changes could be made to improve this experiment?
2. Write an essay describing the relationship between ABA, GA₃, seed germination and development.
3. Design a poster that presents and explains the experiment and its findings.
4. Make a concept map utilizing the information from reading and this lab.

Extension / Reinforcement / Additional Ideas to top
 

1. Use a graphing calculator to analyze the data.  How would it compare to a hand constructed graph of the same data?
2. Work in conjunction with a calculus teacher in order to determine the precise quantity (area) of starch digestion.
3. Which other experiments can be suggested for studying factors that affect seed germination?  How can this information be useful for further study of plants?
4. Most of the literature focuses on plant hormones in monocots.  A dicot, such as a bean plant, could be examined using the same protocol developed in this investigation.
5. In order to determine the effects of abscisic acid and gibberellic acid already present in the seed, the embryo could be removed with a scalpel or razor blade.  To illustrate the importance of these two hormones, the amount of starch could be compared between those with the embryo present and those with the embryo removed.  To take this another step further, students could use ABA and GA₃ to attempt to simulate the conditions present during typical seed germination.
6. Students could research the hormones abscisic acid and gibberellic acid to determine their roles in plant development.  For example, do these two hormones have roles in plant dormancy?
7. The other three classes of plant hormones are: auxin (indol-acetic acid or IAA), cytokinins, and ethylene.  Investigate the effects of these hormones on plant growth and development.
8. Students could study the effect of varying concentrations of hormones on seed germination.
9. Extend the investigation to research on or discussions of  farming, harvesting of fruits and vegetables, hydroponics, hormones and selective breeding, the world's food supply, green revolution, agriculture in areas of famine, etc.

References Including Web Addresses to top

1. Anderson, H.M., and Christine Cooke.  "Plant Hormone Action Group."  Integrated Approach to Crop Research - Long Ashton Research Center.  1997.  <http://www.lars.bbsrc.ac.uk/plantsci/hag.html>  20 July 1998.  [good reference site]
2. Bleakney, Ian.  "Investigating Seed Germination and Tropisms." Life in Motion: The 1998 Woodrow Wilson Biology Institute.  1998.  <http://www.woodrow.org/teachers/biology/institutes/1998/presentations/bleakney/>  19 July 1998.  [student questions]
3. Crocker, Steve.  "Plant Hormones."  University of Bristol Long Ashton Research Station.  1996.  < http://www.plant-hormones.bbsrc.ac.uk/>  19 July 1998.  [good reference site]
4. Davies, Peter J.  Plant Hormones: Physiology, Biochemistry, and Molecular Biology.  2nd ed. Dordrecht, Netherlands: Kluwer Academic Publishers, 1995.  [concentration of hormones]
5. Davis, Jeanine M.  "Organic Sweet Corn Production."  North Carolina State University's North Carolina Cooperative Extension Service Department of Horticultural Science.  1998.  <http://www.ces.ncsu.edu/depts/hort/hil/hil-50.html>  20 July 1998.  [temperature of experiment]
6. Jacobsen, J.V., and L.R. Beach.  "Control of transcription of a-amylase and rRNA genes in barley aleurone protoplasts by gibberellin and abscisic acid."  Nature.  316 (July 18, 1985): 275-277.  [graph of relationship between hormones and a-amylase production]
7. Riley, John M  "Gibberellic Acid for Fruit Set and Seed Germination."  California Rare Fruit Growers, Incorporated.  1997.  <http://crfg.org/tidbits/gibberellic.html>  20 July 1998.  [function of gibberellic acid]
8. Ross, Cleon W.  "Detection of Gibberellin Stimulated Amylase Release from Barley Half Seeds in Starch Agar."  Plant Physiology Laboratory Manual. Wadsworth Publishing Company, Incorporated, Belmont, CA, 1974.  [experimental design]
9. Scott, Peter.  "Lecture 4 - Plant Tissue Culture I: Effects of Plant Growth Regulators in vivo."  Sussex University Biology Department. <http://www.biols.susx.ac.uk/Home/Peter_Scott/Plant%20genetics%20course%20details/LECT_04/PGLECT4.HTM> 14 July 1998.  [seed and hormone diagrams]
10. "Sigma-Aldrich Chemical."  Sigma-Aldrich.  1997.  <http://www.sigma.sial.com/>  20 July 1998.  [chemical supplier]
11. Takahashi, Nobutaka.  Chemistry of Plant Hormones.  Boca Raton, Florida: CRC Press, Inc., 1986.  [reference]
12. "WWWebster Dictionary."  Merriam-Webster Online.  1998.  <http://www.m-w.com/netdict.htm>  20 July 1998.  [glossary]

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If you have any questions about this lesson, please click on any of the authors' names at the top of this page to contact them by e-mail.

Click here to return to the home page of the 1998 Woodrow Wilson Biology Institute "Life in Motion: Movement in Biology at all Levels of Organization."