Students will design, perform, and document their own experiment examining the effect(s) of a plant growth regulator (PGR). All students are expected to have a basic understanding of a variety of PGRs based on an introductory worksheet. Students are then divided into groups of 2 – 4 to do additional background research on one PGR that they have been assigned. Each group will then design a specific hypothesis about the effects of their assigned PGR using their choice of monocots and/or dicots in different stages of development. Data analysis and write-up can be done collaboratively or individually if used as a summative assignment. Students’ understanding of plant growth regulators and the nature of scientific inquiry can be reinforced with an optional mini-conference after submission.
Grade 11 University Preparation Biology, SBI3U
Plants - Anatomy, Growth, and Function
How do plant growth regulators influence the growth of plants?
Prior preparation: Different groups will be using seeds or young plants of different ages. Depending on growing conditions available and the age of plants that students want to use, preparation for this lab may need to start >2 weeks in advance. Students may want access to anything from dry seeds (no preparation required) to young plants with true leaves (>2 week old seedlings). Having a few easy-to-culture species in different stages of development on hand is advisable. One or two varieties of monocot and one or two eudicots is suggested; starting seeds in 3 – 5 day intervals 2 to 3 weeks prior to the experiments’ set-ups will provide a range of developmental stages by the time the experiments need to be set up. Furthermore, there must be enough seeds started to provide several replicates for each treatment. It is suggested that each group have access to 20 – 30 seeds or 10 – 20 cuttings to be assigned to 2 to 4 different treatments.
Day 1 – Introduction & Background: A hook and diagnostic assessment will engage students in the topic. At least one class will be needed for students to acquire the background knowledge and vocabulary to devise specific, measurable, and informed hypotheses. Students will acquire an understanding of how seeds germinate and enough knowledge of the parts of a seedling to design specific measurement methodology (e.g., ‘epicotyl, hypocotyl and radicle lengths’ instead of ‘size of seedling’) that will be more likely to result in useful data. (Handouts: Seed & Seedling Anatomy: Monocots and Eudicots; Introduction to Plant Growth Regulators)
Day 2 – Experimental Design: One class will be needed for students to do additional background research for the plant growth regulator that they will be testing and to design their experiment. Specific questions are suggested to improve the level of detail students will use in their design, but this list is not complete and should be used as a guide to students asking their own questions in order to ensure an appropriate level of detail in their methodology. (Handouts: Plant Growth Regulators Research; Plant Growth Regulators: Experiment Design).
At least one copy of each group’s handouts should be handed in prior to the experiment’s set-up to ensure that the design is feasible, clear, and detailed enough to minimize set-up delays, and to have a complete and accurate list of materials.
Day 3 – Experimental Design Check In: Ideally, meeting with each group in class will address any concerns. A self-directed lesson (e.g., differences between monocots and eudicots, biological drawings work period) can ensure other groups are productive while waiting their turn for their in-class meeting. Alternatively, groups can meet with their teacher outside of class time, particularly if a group needs a significant amount of support.
Day 4 – Set Up and Data Collection: One class will be allocated to set up the experiments. Subsequent data collection can be done either at the beginning of classes that follow the set-up, or at a designated ‘data collection’ time (e.g., lunch hour, before or after school). It is advised that all members of a group have copies of the data at all times and/or that the data are posted in an electronic document to minimize the risk of data loss. (Handout: The set-up diagram and data table are to be designed as items 4 and 5 of the Plant Growth Regulators: Experiment Design handout.)
To ensure adequate time for plant growth and data collection, time should be provided in class during the next 2 weeks. If equitably shared by all group members, 10 – 15 minutes of class time should allow for data collection and plant maintenance. The remainder of the class time in these 2 weeks can be used for other lessons in the teacher’s lesson sequence for the unit. For example, students will start the class with their data collection and, as they finish, they will get out microscopes, slides, and reference materials to study the differences between monocot and dicot leaves, roots, and stems.
Day 5+ – Analysis: After approximately 2 weeks of data collection, at least one full class can be allocated for data analysis. Group members will ensure that data were accurately shared, discuss their results, and design a way to best display their results. Depending on student needs and teacher preferences, this may include a table and/or a graph. If a table is used, it is expected to show some data processing and not simply a neater copy of the original data.
Pending student needs, teacher preferences, and time constraints, the lab can be written up as a ‘full’ science lab write-up with an introduction, methods, results, and discussion sections. In this case, homework time should also be allocated for the write-up. The scaffolded response alternative to the full write-up (provided) can be completed in class. Either can be done as a group or individually. If this inquiry project is to be used as a summative evaluation, students can complete their graph and/or table and the Plant Growth Regulator Experiment Write-up handout individually during one or two class periods as they would for a test so they can be evaluated individually.
PGR Conference: Students present their experimental results to each other in a round-robin or jig-saw style mini-conference, with individuals from each group presenting to peers in small groups. This will allow additional feedback about experimental designs, will reinforce the range of PGRs’ effects on plants, and provide a broader view of the challenges of real research. (Handout: PGR Conference Summary) Students will be required to bring all their handouts, research, and data analysis for reference to the conference, but no additional preparation is required for this format.
Plants have specialized structures with distinct functions that enable them to respond and adapt to their environment.
- F2: Investigate the structures and functions of plant tissues, and factors affecting plant growth
- F3: Demonstrate an understanding of the diversity of vascular plants, including their structures
- F2.1: use appropriate terminology related to plants, including, but not limited to: … stomata, auxin, and gibberellin
- F2.2: design and conduct an inquiry to determine the factors that affect plant growth
- F2.4: investigate various techniques of plant propagation
- F3.2: compare and contrast monocot and eudicot plants in terms of their structures and their evolutionary processes
- F3.3: explain the reproductive mechanisms of plants in … artificial propagation
- F3.4: describe the various factors that affect plant growth
- Monocot and Eudicot seeds and seedlings differ in several fundamental ways.
- Different plant growth regulators have different effects on plants.
- Factors such as solution concentration, age of plant, and target tissue type will influence the type of impact a particular plant growth regulator will have on a plant.
- The success of the experiment and data quality depend on many factors within our control (e.g., concentration of reagent, number of replicates, skill in measurement, duration of experiment, horticultural skills).
- Seed germination depends on species-specific optimal ranges of factors such as temperature, light, moisture, and growth regulators; it can be influenced by techniques such as pre-soaking seeds, nicking the seed coat, using anti-fungal agents or strategies.
- Plant growth depends on species-specific optimal ranges of factors such as temperature, quality and quantity of light, moisture and drainage, soil texture, and nutrients.
Prior Skill Sets:
- Internet and/or library research skills
- APA citation (in text and literature cited section)
- Collaboration skills
- Basic laboratory safety (WHMIS/ chemical handling, handling glassware, correct labelling)
- Reading/understanding Materials Safety Data Sheets for reagents
- Making solutions, calculating concentrations of solutions, making dilutions
- Experimental design skills (hypothesis generation, choosing treatment levels, the control treatment, and sample size)
- Data table design and construction
- Graph design and construction
- Data interpretation
- Basic plant anatomy (stem, root, leaf, shoot, and root apical meristems)
- Experimental design terminology (dependent/ independent/ controlled variables, treatment(s), treatment levels, control treatment, sample size)
Materials and Equipment:
Computer and/ or Library access: for research time on Day 1; Background on Day 2; Experimental design (Access is optional on subsequent days for recording data and lab write-up.)
Seeds: If using seeds, these should be large enough to be easily seen, handled, and measured; larger seedlings will permit students to differentiate between different parts of the seedling (e.g., radicle, epicotyl, hypocotyl) when observing effects of hormones. Students may have a specific species required for their experiment, but should consider the following suggestions:
- Easily obtainable Monocot seeds include sweet corn, wheat berries, and oats. Larger Eudicot seeds could include beans (fava, lima, kidney), peas (chick, green), or even the seeds of dates or avocados that students can collect themselves. Many of the dry seeds mentioned are available in bulk food stores year round, but should be tested beforehand to ensure that the seed will still germinate.
- Some seeds (usually smaller seeds) require light to germinate while others may be inhibited by light. Similarly, roots are often repelled by light and may grow away from a clear sided vessel. Background research on the optimal requirements of the species that students are trying to grow is strongly advised. Preventing or providing light as a controlled variable may be required for promoting measurable growth.
- While some seeds are often easy to obtain at any time of year or can be stored for many months until needed, live plant material may be another option that students can try. Houseplants are available at any time of year, but other living material can only be obtained at certain times of year. Some can be stored for several months, but advance preparation is essential. Easy-to-find materials for vegetative propagation include strawberry or spider plant runners, potatoes (cut out individual eyes with an attached piece of tuber rather than using the whole potato) or garlic from one’s kitchen, stem cuttings from common houseplants, such as jade plant or ivy, leaf cuttings from African violet or begonia. During spring or late fall, cuttings from common garden plants and shrubs, such as mint, dogwood, and serviceberry, can also be used. Consult a garden centre or experienced gardener about what is available in your area at the time of year you are planning to do this experiment.
Containers and media: Containers and growing media used to grow plants will vary a great deal depending on the type of seed or live material used and how large these will get during the duration of the experiment. Consulting a gardener or resource on plant propagation is suggested. CD cases containing moistened paper towel or cotton batting can be used for smaller seeds and shorter time periods. Other containers can include test tubes, plastic egg cartons, clear plastic or glass jars, or tubs used for dairy products. Garden centres or mail order and scientific supply companies offer a wide range of clear or opaque containers that may be suitable. Growth media to support the growing seeds or cuttings can include perlite or vermiculite which can be gently shaken or rinsed off developing plants without damaging them. Placing cuttings or seeds against a clear sided vessel can allow for observations without dislodging the plant. You may also be able to modify hydroponic systems to your advantage for larger cuttings.
Measuring tools: The best measuring device may vary with the type of plant used and the part of the plant that is to be measured. Tape measures will allow for the measurement of curved stems or roots. Vernier calipers may be needed for very short distances. Small rulers are only appropriate for short, straight distances.
Water: Watering should be done with de-chlorinated water at room temperature but tap water left out overnight will suffice. Rainwater or spring water of known composition may provide better results. The optimal amount of water used will vary depending on the needs of the species being used and how quickly evaporation takes place in the conditions provided. Overwatering will result in mouldy, dead seedlings. Care must be taken not to dislodge seeds or seedlings, so a gentle spray, dripping or wicking of moisture via the growth media is preferable to a heavy stream of water.
Plant Growth Regulators: Students will be assigned a specific PGR or 2 PGR combination after they have done basic research on the effects of each hormone on the Introduction to Plant Growth Regulators sheet. While natural concentrations of PGRs in plants are often in picomolar concentrations, this can increase greatly (e.g., ~1000x, for cytokinins) if the plant is stimulated to produce PGRs by damage or environmental stimuli. Some concentrations are suggested in the table below, but it is suggested that students are provided with a more concentrated version (10 – 100x) of hormones that they can dilute to the level they require based on their experiment. Solutions and dilutions should be made only with distilled water, but some PGRs must first be dissolved in alcohol before diluting with water. Follow manufacturers’ preparation methods. Suggested concentrations may be provided with products themselves; commercial versions purchased at garden supply stores are already mixed. (See Appendix 1 for suggested suppliers.) Ethylene is a gas and, while available for order, it will be difficult to control concentrations; both ethylene and brassinosteroids are prohibitively expensive for classroom use.
Students are expected to identify the concentration(s) and amount(s) of hormone they will be using during their experiment. Students should also receive a copy of the Materials Safety Data Sheet (available online from the supplier or as a hardcopy with your shipment) for their assigned PGR to facilitate their planning.
Abscisic acid (ABA)
Physiological levels: ~2 µg / g fresh weight of tissue
Gibberellic acid (GA)
100 ppm or 100 mg / litre of water
Indoleacetic acid (IAA)
Physiological levels: ~1.5 mg/ g fresh weight of tissue
Indolebutyric acid (IBA)
~15 µg/ l of water
Cytokinin (variable depending on type of cytokinin available)
1 nanomole/ litre of water
Safety is a component of students’ experimental designs. Before students are provided with any materials or equipment, they will have done research on and provided the teacher with basic safety considerations for their specific experiment. The factors they identify should include the following:
- Allergic reactions may be caused by some seeds or plant materials. Check students’ medical information and your school or board directives on the use of plants in the classroom.
- Chemical safety will vary with the PGR or other treatments used. Carefully read any accompanying safety information (e.g., MSDS). Solutions should be labelled appropriately and suitable safety equipment provided for student use (e.g., gloves, goggles, pipettes). As the reagents can be very expensive, it is advised that the teacher prepare standard solutions for student use and label the containers appropriately.
Other concerns will vary with students’ specific experiments and the containers in which they will grow their plants. For example,
- Particulates from the growth media (e.g., perlite, vermiculite) may be irritants for eyes or respiratory system.
- Hazards may result from the possible breakage of growth containers. Plastic containers are preferable to glass to avoid risks associated with breakage.
- Blades may be used to cut live plant material, but the type used will vary depending on the experiment.
Instructional Planning and Delivery:
Day 1 – Introduction: One or more of the following options can be used as a diagnostic activity for prior knowledge or as a way of engaging students’ attention:
- On a blank sheet of paper, sketch a typical plant and a typical seed, and label any of the parts that you know. (Students can be given models from which to draw, such as kidney beans and live or pressed dried plants, or can be given unlabelled diagrams.)
- List the changes that you might see in a plant from day to day or week to week that show that it is alive. How do you think a plant knows when these changes should occur? How do you think these changes are controlled?
- Question brainstorm: Carefully examine the seeds and seedlings provided. Record any questions that come to mind while you are examining them, even if you can answer those questions with a little more examination. (Provide students with samples of ungerminated and germinated seeds. Include monocot and dicot seeds and seedlings at different stages of development, if possible.)
These activities will also provide diagnostic information about students’ prior knowledge.
Background: Students complete background research to familiarize themselves with terms and concepts needed to devise a hypothesis and testable experiment.
Seed & Seedling Anatomy: Monocots and Eudicots
Introduction to Plant Growth Regulators
Homework: Students are to complete handouts, if incomplete, and review experimental design terms.
Day 2 – Experimental design: Experiment teams assigned (2 – 4 suggested). Groups are assigned the hormone(s) they are to study. Internet/ library research time allowed for more detailed background information on their assigned hormone(s) to allow an informed hypothesis to be generated (Plant Growth Regulators Research handout, Plant Growth Regulators: Lab Design). Students may want to divide the questions among group members and will use their research to devise questions individually prior to reuniting as a group to choose a final research question and devise their hypothesis and methodology together.
Students should be encouraged to use specific terminology learned in the Seed & Seedling Anatomy handout when describing how the treatments are applied and how measurements are taken. APA-cited support for the justification of their hypothesis is expected. Students may also base their methodology on cited sources.
A preliminary team meeting can be held during this class to provide research support and guidance for the design of the experiments.
Homework: Students complete Plant Growth Regulators: Experiment Design, if not already complete. Students will need to collect any materials that are to be brought from home (e.g., specific types of seeds, plant material, or planting pots they propose that are not provided in class).
Day 3 – Experimental design check-in: The student who is responsible for gathering materials will notify the teacher of equipment requirement details and one copy of the lab design. The teacher will review the students’ designs to ensure that there is enough detail and available equipment to allow for the successful execution of the experiment and to allow time for modifications, if needed. The availability of PGRs or other equipment may limit the amount of flexibility the teacher can provide for students’ experiments. For example, students may have to use a standard concentration of PGR prepared for all groups to use if they request a prohibitively expensive concentration of PGR.
Day 4 – Set-up and data collection: Students use provided equipment described in their design to set up their experiment. Data table to be designed and first measurements taken.
Ongoing – Data collection: It is suggested that students collect their data, water their plants, and check for dead plants/ seeds in the first 10 – 15 minutes of the subsequent 2-3 weeks of class. Alternative arrangements may have to be made outside of class time to accommodate differences between students’ experiments. Experiments may be restarted if changes to the experimental design are needed, if results are visible in a shorter time period or if seedlings die unexpectedly.
Day 5+ - Analysis: A work period can be used for pooling data, creating tables, graphs, and whatever data analyses are needed. MicroSoft Word (tables) or Microsoft Excel (tables, graphs) can be used or this can be done by hand. This work can be done individually or in lab groups, depending on how the product will be evaluated. Be sure to inform students that their table will probably not be identical to their original data collection table. The lab write-up can be completed as homework, done individually or as a group in class, again depending on how it will be evaluated. An optional mini-conference will allow students to share their experiences in small groups.
Related Background Resources:
Basra, A. S. (ed.) 2000. Plant growth regulators in agriculture and horticulture. Haworth Press. New York
Campbell, N. A. and J. B. Reece. 2002. Biology. 6th ed. Benjamin Cummings. San Francisco
Clouse, S. D. and J. M. Sasse. 1998. Brassinosteroids: Essential Regulators of Plant Growth and Development. Annual Review of Plant Physiology and Plant Molecular Biology 49: 427-451 DOI: 10.1146/annurev.arplant.49.1.427 http://www.annualreviews.org/doi/abs/10.1146/annurev.arplant.49.1.427?journalCode=arplant.2
George, E. F., M. A. Hall, and G. De Klerk (eds.). 2008. Plant Propagation by Tissue Culture 3rd Edition Vol. 1. Springer. Dordrecht
Roberts, J., S. Downs, and P. Parker. 2002. Ch. 5 Plant growth and development. IN Ridge, I. Plants. Oxford University Press. Oxford
Smith, M. 2007. The plant propagator’s bible. Rodale Inc. Emmaus
Whipker, B. E. 2013. Plant growth regulator guide. (multiple articles) Grower talks magazine. 2013: 1-37. http://www.ballpublishing.com/pdf/PGR_GUIDE_2013-LowRez.pdf
Various authors: Links to many peer-reviewed articles relating to specific PGRs are available on Sigma-Aldrich’s website at the bottom of the page for each. http://www.sigmaaldrich.com/life-science/molecular-biology/molecular-biology-products.html?TablePage=9435344
General Web Resources:
Biology online. http://www.biology-online.org/3/5_plant_hormones.htm
Website for: Taiz, L., E. Zeiger, I. M. Moller, and A. Murphy (eds.). 2015. Plant physiology and development. 6th Ed. Sinauer. Sunderland. http://6e.plantphys.net/
At various stages of the inquiry, the teacher’s observations of and conversations with individual students or lab groups at work can provide insight into students’ understanding of terminology, experimental design, and level of participation in and understanding of the inquiry process (Initiating & planning, Performing & recording, Analysing & interpreting, Communicating). Assessment for Learning Record sheets are included below.
Products that can be assessed for learning (and assessment tools) during this inquiry process include Seed & Seedling Anatomy: Monocots and Eudicots (Homework Rubric) and the Introduction to Plant Growth Regulators (Homework Rubric). Other components of the inquiry may be evaluated for learning, as learning, or of learning if the inquiry is to be used as summative work.
Self- and peer-assessment opportunities include collaboration skills (Checklist), homework completion skills for introductory background work (Homework Rubrics for Seed & Seedling Anatomy: Monocots and Eudicots, Introduction to Plant Growth Regulators), research skills (Plant Growth Regulators Research Assignment Rubric), planning skills (Marking Scheme for Plant Growth Regulators: Experiment Design), and pre-submission assessment of the final submission (Marking Scheme for Plant Growth Regulators Experiment Write-up).
This inquiry can be used as a summative assignment for the Plant Anatomy and Function Unit or as a summative laboratory component for the course, as evaluations are mainly based on transferrable inquiry and communication skills that would have been developed across units throughout the year and only some unit-specific content. Parts of this inquiry (and evaluation tools) that are suitable for evaluation purposes include Plant Growth Regulators Research (Assignment Rubric), Plant Growth Regulators: Experiment Design (Marking Scheme), and the Plant Growth Regulators Experiment Write-up (Marking Scheme).
Future Opportunities/ Extensions:
Transferrable skills that can be reviewed or re-assessed include collaboration, research, experimental design, table and/or graph construction, data analysis, lab materials handling and safety.
The role of growth regulators can be linked to their roles in tropisms, propagation (natural and artificial), and the evolution of plants both in this unit and the Evolution unit in this course (SBI3U).
The role of hormones to the development, growth, and life stages in plants is analogous to that of hormones in humans as addressed in the Homeostasis unit in SBI4U and the Healthy Living strand in Ontario’s Health and Physical Education curriculum.