Summary/Abstract
Instructor's Objectives
- define the term tropism.
- name three different types of tropisms exihibited by plants.
- explain the role of auxin in plant root growth.
- evaluate the importance of gravity in root growth.
- form hypotheses and set up an experiment to test their hypotheses.
Target Audience
Biology: grades 9 - 12Notes to Teacher
This activity calls for a turntable (record player) to rotate the beans as they are germinating. If a turntable is not available, any device which will spin the beans at about the same speed will work just as well. The protocol also says that the beans must stand for three days in the aluminum foil before spinning the beans. Try to have the students prepare the aluminum foil packets on a Friday, therefore the beans can stand undisturbed over the weekend and be ready to go on Monday morning. Also, if only one turntable is available, this could be done as a demonstration by the teacher. If pinto beans are not available, raddish seeds, corn, and peas could be used instead.Materials
16 pinto beansglass or beaker
paper towels
record player
Background
Student Lab
Teacher preparation:- Place the beans in a beaker or glass filled with water (tap water is fine).
- Allow the beans to soak in the water in the refridgerator overnight.
Student Lab Procedure:
- Tear four pieces of aluminum foil that are about one-foot (30 cm) square.
- Moisten a paper towel with water (the paper towel should be damp, not dripping wet!)
- Place the paper towel in the middle of each piece of foil.
- Get four beans which have been soaked overnight by the teacher, and place them in the center of each paper towel
- Fold the aluminum foil around the paper towel and close each end of the foil, forming a pouch with the beans inside (You might want to place a piece of masking tape on your packet and write your name on it, since there will be more than one packet on the turntable). See Figure C below.
- Let the bean packets stand undisturbed for 3 days.
- Place the seed packets, evenly spaced, on the turntable.
- Turn the record player on and place it on 75 rpm.
- Allow the record player to rotate continuously for 5 days.
- After 5 days, turn off the record player, obtain your seed packets.
- Open your packet and make observation about the direction of root growth. See Figure D below.
(copied with permission from Biology for Every Kid by Janice Van Cleave)
Evaluation/Assessment
There are a couple of different ways that this activity can be assessed:- Students can be assigned a journal which must be kept and updated throughout the activity. This observation log can include their hypothesis which was formed before the activity was started. Being good amateur scientists, they might also include a detailed description of the actual lab set-up and equipment used. It can also include all of the post lab observations that they make concerning the seeds. Students would also include their rationale of whether or not their hypothesis was correct. A rubric could be used to grade this form of assessment, such as: 20 pts for their hypothesis; 20 pts for a detailed description of the set-up; 40 pts. for detailed observations of the beans after 5 days of spinning - this would include drawings of the seeds after the experiment; 10 pts. for student rationale defending or rejecting their hypothesis; 10 pts for overall neatness of the journal.
- A post lab quiz could be given to assess student achievement. The following questions could be asked:
1. Name 3 other tropisms that plants exhibit in response to their environment. Also, name what each
tropism is in response to (e.g., thigmotropism - response to touch).
2. What effect, if any, did spinning have on the beans?
3. Describe the role of the plant hormone auxin in the growth of a plant.
4. What do you think would happen if you reversed the direction that the
beans were spinning?
Explain your answer.
5. Design an experiment that would test one of the other tropisms that
you named in question #1.
- Since one of the steps of the scientific method is communicating, the students could present their results to the entire class. In their presentations, they must state their original hypotheses, present their results using visual aids (posters, overheads, graphs, etc.), and relate their results to the overall theme of plant movement. Again, a rubric could be used to grade this method of assessment: 20 pts for statement of original hypothesis, 30 pts for visual aids, 30 pts for statement of results, and 20 pts for overall effectiveness of presentation (clarity, smoothness, etc.).
Extensions
This lab activity can modified into an inquiry based activity in which the students must design a lab to test their hypotheses. In order to do this, the teacher can discuss the role of plant hormones, such as auxin, with the students. At that point the teacher could ask the class what else they want to know about tropisms and write the student generated questions on the board. The students would then form hypotheses about whichever tropism they wanted to investigate. Give the students the presoaked beans, have them design an experiment to test their hypothesis, and then actually set-up and run the experiment. Students would gather data throughout their experiment and present their results to the class.References
Additional Links
http://biocomp.arc.nasa.gov/people/jeff/.index.html - Current research on gravitropism by Jeffrey Smith, a Ph. D. at NASA.http://trc.ucdavis.edu/Coursepages/EXCITES/ls.html - Another gravitropism experiment using Wisconsin fast plants.
http://www.aspp.org/education/labexer.htm - Lab activity using corn seeds to demonstrate gravitropism.
http://eruditio.asu.edu/~smckeeve/scilinkbio.html#Plants - Other plant links and activities using plants
http://www2.ncsu.edu/unity/lockers/project/ncsu-nscort/public/outreach/teach/outline.html
- Home page of the NASA Specialized Center of Research and Training in
gravitational biology at NC State University.