Pollen germination as a model system for teaching the process of science to undergraduate non-science majors in an investigative laboratory.
KEY WORDS: Investigative laboratory, science education, pollen
Over the past few decades, there has been considerable interest in developing new strategies for teaching undergraduate science laboratories. Traditionally, students in science laboratories follow a proscribed series of recipe-like steps, usually printed in a manual, to observe and verify concepts and processes discovered by others. Such "cookbook labs" have served as the background for developing new laboratory exercises that give greater emphasis to problem-solving skills and applications of the scientific method. For example, in "open-ended labs," students use the results obtained in a traditional laboratory to conduct follow-up experiments of their own choosing. In "inquiry-based labs," students solve a series of "What happens if..." questions posed by the instructor. In "investigative labs" students design and carry out an entire research project (Sundberg and Moncada, 1994).
The investigative laboratory, or I-lab, has been particularly effective in promoting student learning of both the process and content of science. Although many variations of the I-lab model exist, the basic plan for such a course, as described in what is still the classic reference for I-labs (Thornton, 1972a), is as follows:
1. Students are told that the purpose of the course is to help them conduct a research project of their choosing, and the instructor designs a series of exercises to prepare the students for this task.
2. In consultation with the instructor, students (either individually or in groups) formulate a problem and the experimental plan for solving it.
3. Students carry out their experiments over a period of time sufficiently long that experiments can be repeated, and the direction of the work can be modified if necessary.
4. The laboratory terminates with the submission of written and! or oral reports.
The evidence suggests that in I-labs, which emphasize student creativity and decision-making, students learn the desired concepts at least as well as students in traditional laboratories, and student satisfaction is much higher (Leonard, 1994). Because they emphasize procedures utilized by practicing scientists, such as hypothesis formation, manipulation of experimental variables, and data analysis, I-labs respond to the report, Project 206l: Science for all Americans, in which the American Association for the Advancement of Science recommends that science curricula include greater emphasis on the process of science rather than strictly content (American Association for the Advancement of Science, 1989). That is, students should experience science firsthand instead of merely being told about it (Thornton, 1972a).
One problem noted by instructors of biology I-labs is that students are often overwhelmed by the freedom to choose their own experimental problem. As a result, they cannot identify a suitable project, and potential experiments gleaned from journal articles are beyond their levels of expertise. This problem can be solved by providing the class with an experimental system for which some of the background work has already been carried out (Thornton, 1972b). By using such a "model system," students do not have to start from scratch, spending what might be the entire semester on tasks such as selecting an experimental organism, determining the optimal environmental conditions for maintaining it, and accumulating the appropriate apparatus for conducting the experiments. Care must be taken, however, to find a model system that is 1) simple enough to used by non-majors and 2) complex enough to maintain their interest for an entire semester. In this paper, I explain how pollen grain germination can be used as an effec tive model system for an I-lab. In addition, I describe how the I-lab concept can be used to teach the scientific method to students who are not majoring in a science program.
MATERIALS AND METHODS
In the Spring 2002 semester I taught an honors seminar for first- and second-year non-science students. Fifteen students were enrolled, and all were taking the course to partially fulfill the science requirement in the College of Arts and Sciences at Rutgers-Camden. There were no prerequisites for this course, but all of the enrolled students had taken biology and chemistry in high school. The course met once per week for two and one-half hours.
The seminar was entitled "Science in Action," and it was taught entirely in the laboratory with the goal of giving students an idea of what it was like to "do" science. Because science involves venturing into the unknown -- to attempt to discover new concepts -- I wanted students to work on a problem for which neither they nor I knew the solution beforehand. This system not only would mimic the process of science as carried out in a research laboratory, but it also would provide the potential for that "Eureka!" moment of discovery that is one of the joys of being a scientist.
When designing the course I had two concerns. First, how could I provide non-science students with the skills, motivation, and tolerance of frustration necessary to carry out a research project? Second, what model system would be appropriate for my students to use?
Pollen grain germination was used as a model system
The decision to use pollen grains resulted from the need in a previous semester to demonstrate pollen tube growth in an upper-level botany course. One of the "classic" botany lab manuals (Bold, 1967) indicated that pollen grains could generally he germinated in sugar solutions (1-15 %) with or without 1.5% agar. However, when I tried these procedures on Gladiolus pollen, only about 5% of the grains germinated. Because of my background (Garraway and Evans, 1984) in the nutrition of fungal spores and hyphal germ tubes (which superficially resemble pollen tubes), I suspected that the incubation medium lacked some critical nutrient, and I thought determining what it was would be a good I-lab exercise for my seminar students.
Pollen grains, particularly from Gladiolus, turned out to be ideally suited for the I-lab project. Gladiolus flowers are inexpensive and can readily be obtained year-round from florists. The anthers are large and easy to work with, the pollen is powdery and easy to harvest, and the grains are not sticky as is other pollen such as Lily. When germination takes place, it occurs within a 24-h period, and thus students can set up an experiment one day, incubate the pollen at room temperature overnight in a moist chamber, and then examine the results the next day. The short germination time obviates the need for preparing sterile incubation solutions. If the class schedule prevents students from examining the pollen after 24 h, the moist chamber containing the pollen grains can then be refrigerated for as long as one week without complications arising. The pollen grains are relatively large and easily seen under the compound microscope using the 10X objective. When germination occurs it is quite striking, with long pollen tubes -- sometimes traversing the entire field of view -- extending from each grain. The major problem is the occasional clumping of the grains which causes difficulty in accurately determining the percentage germination.
The first several classes were used to provide background information
Because the students had little background in science, a few class periods were used to provide the necessary background information. Four main topics were covered: 1) background information on pollen and plant nutrition, 2) the scientific method and design of experiments, 3) proper laboratory technique, and 4) statistical analysis of data.
1. Background information on pollen and plant nutrition
As a class, we dissected Gladiolus flowers and examined the pollen under the microscope. I presented a general introduction to sexual reproduction in angiosperms, including the transfer of pollen from the anther to the stigmatic surface of the pistil, the potential for pollen-stigma recognition, the germination of the pollen grain, and the resulting growth of the pollen tube. I explained that in previous experiments we had attempted to germinate pollen grains in vitro, but the simple germination procedure described in the lab manual was ineffective for Gladiolus pollen. I also mentioned that a quick review of the literature (e.g., Brewbaker and Kwack, 1963; Schimpf, 1992; Taylor and Hepler, 1997; Raghavan, 2000; Tse and Chan, 2001) indicated that pollen from a wide assortment of species would in fact germinate in vitro when incubated in a growth medium containing a carbon source such as a sugar and a few mineral salts. Thus, Gladiolus pollen might germinate if provided with the proper combination of mineral s alts along with the proper carbon source, and I suggested this might be a good place to begin our experiments.
To aid in choosing the proper mineral salts, I briefly described the essential elements required by most vascular plants, categorizing them as either macronutrients (C, H, O, P, K, N, S, Mg, and Ca) or micronutrients (Cl, Fe, B, Mn, Zn, Cu, Ni, and Mo) (Raven et al., 1999). I also discussed typical sugars used as carbon sources, including monosaccharides (such as glucose, galactose, and fructose) and disaccharides (such as sucrose, maltose, and lactose). Lastly, I speculated that other factors could be involved, such as pH, temperature, light, and oxygen, and that students would be free to investigate any parameter they wished, once the class as a whole made some preliminary studies.
Emphasis was placed on using pollen as a model system, and the process followed would be similar to that used as the first step in studying any phenomenon. That is, regardless of the long-term goal, one must first develop some baseline parameters before proceeding with more sophisticated experiments. For example, if one wished to investigate gene expression in germinating pollen grains, one would first need to develop a way to consistently obtain a high percentage germination.
2. The scientific method and the design of experiments
Emphasis was placed on how to construct an hypothesis, design a controlled experiment to test that hypothesis, and draw logical conclusions from the resulting data. Students were asked to design their experiments using a standard format (Figure 1) that contained the following parts:
a. An experiment number to provide a reference.
b. A one sentence statement of the purpose of the experiment.
c. A plan showing the logic of the experiment in terms of the various treatments. Of particular importance were: 1) the proper control as a basis for comparison, 2) sufficient replicate treatments for statistical analysis, and if appropriate, 3) a range of concentrations to maximize the chance of identifying the optimum.
d. A list of the procedures to be followed.
The class was given an assortment of pencil-and-paper exercises to practice experimental design.
3. Proper laboratory technique
Proper laboratory safety and selected laboratory techniques were discussed and demonstrated. Emphasis was placed on deciphering chemical labels, disposing of chemical wastes, wearing proper laboratory attire, and using pipettes, the analytical balance and other equipment. Students were instructed of the importance of keeping a laboratory notebook having sewn pages, and such a notebook was required for the course.
In addition, one laboratory session was devoted to learning how to prepare solutions. Because students would be conducting their own experiments, they would need to prepare their own solutions. However, most students were used to "cookbook labs," and thus they had little experience doing the calculations for preparing the desired solutions and making the appropriate dilutions. Once again, paper-and-pencil exercises were used to provide practice.
4. Statistical analysis of data
Discussion centered on how to deal with variability, particularly the considerable variability one finds in biology. Standard error (SE) was introduced as one relatively simple statistic for analyzing biological data, and this led to a brief discussion of mean, variance, and standard deviation. Emphasis was placed on using histograms with SE bars to aid in the analysis of experiments. The rule to be followed was this: if the SE bars of two treatments overlap, then treatments are assumed to be statistically identical. If the SE bars do not overlap, then the two treatments are statistically different.
The class then went to one of the campus computer labs, and students were shown how to use Excel to prepare histograms with SE bars. Excel was chosen because it is easy to use, most students already have it installed on their own computers, and it is installed on all computers in public areas on campus. Students were instructed to record the percent germination for each replicate treatment in an Excel spreadsheet, use Excel to prepare the corresponding histograms with SE bars on the same spreadsheet, and write an analysis of their experiment directly underneath the graph, using either Excel or their favorite word processing software. The resulting printout, an example of which is shown in Figure 2, would then be taped into their laboratory notebook.
Students worked in groups to carry out identical preliminary experiments
Although students would eventually plan whatever experiments they wished, at the outset of the project I considered it best for the class to do variations on the same basic experiment to ensure that everyone was comfortable with the basic procedures. For this experiment,
I asked the students to work in pairs to test various methods of supporting the pollen grains during the incubation process. These supports included drops of sucrose solution on a microscope slide, drops of a sucrose-agar solution on a microscope slide, filter paper rafts floating on the sucrose solution, and inverted drops of sucrose solution on a microscope slide (called the "hanging drop technique"). After they analyzed their data, each pair of students wrote their results on the board, and we discussed the data as a whole. Although germination was minimal (on the order of 5%), the results differed greatly from group to group, and I used this example of variability to point out the importance of repeating an experiment several times before a realistic conclusion can be made. The take-home lesson was that even when the entire class does the same experiment, it is not surprising that the results will vary because of differences in laboratory technique, pollen freshness, pollen variability, and other factors. The students learned that different results can be obtained even though the same scientific method is used.
For the rest of the semester, students worked in groups and reported their results at lab meetings
Because the class would be working as a research team, I called a "lab meeting" to discuss how to proceed. It was decided to focus first on finding an adequate carbon source for pollen germination and determining an optimal concentration. Accordingly, each group chose a particular sugar from those that were available and designed an experiment along the lines of that shown in Figure 1. They then carried out their experiment, analyzed the results with the help of Excel, then repeated the experiment, and reported back to the class at a subsequent lab meeting.
This basic pattern was then continued for the remainder of the semester. At each lab meeting, which would take place about every three weeks, discussion would center on what direction to take next and how the work would be divided. For example, during one team meeting, a group of students reported that 0.4 M lactose was effective in stimulating germination. Consequently, as a group we decided that the entire class would switch to using 0.4 M lactose as part of a basal medium to which other nutrients would be added. After one group reported that 1 mM [Ca([NO.sub.3]).sub.2] stimulated germination when present with 0.4 M lactose, we decided to test the effect of other nutrients as supplements to this lactose-[Ca([NO.sub.3]).sub.2] medium. Some students chose to test calcium chloride, others potassium nitrate, others magnesium sulfate, and so on. All groups then reported in after they had analyzed their data. Toward the end of the course, students were given the option of venturing out on their own and testing wh atever parameter they wished. This resulted in a variety of experiments in which amino acids and other potential nutrients were tested.
RESULTS AND DISCUSSION
As someone who has taught "cookbook" labs for many years, I was astounded by the increased interest and excitement generated by the I-lab process. In traditional laboratory exercises, the instructor knows the outcome. Although such foreknowledge is often advantageous, one unfortunate consequence is that students may spend their time trying to figure out "what the instructor wants" or "what should have happened" rather than focusing on their own data. However, in this course, things were different. I no longer was the supervisor or someone to be second-guessed. Now, because I didn't know the answers either, I became simply a resource person and even a compatriot. The most frequent question asked of me was, "Here's our experimental plan; what do you think about it?" And my most frequent response was, "Go ahead and try it, because in science you never know what might happen!" Thus, the students' experiments became their own rather than mine, and they quickly took ownership of their work. Perhaps because of this, they were eager to repeat an experiment in order to verify the results. I do not see such enthusiasm in traditional biology labs. In addition, I found my own reactions somewhat surprising. At first I was rather unnerved being placed in a situation in which I did not know the answers to student questions. However, the course soon became an energizing experience as I looked forward to the students finding out something new -- every class was an anticipation of discovery.
The results of the course evaluation showed that students enjoyed the investigative format as well. When responding to the statement, "I learned a great deal in this course," on a scale of 1 (strongly disagree) to 5 (strongly agree), their average response was 4.36, compared to 4.10 for all 100-level courses in the University. When asked to complete the phrase, "I rate the overall quality of the course as... on a scale of 1 (poor) to 5 (excellent), their average response was 4.86, compared to 4.15 for all 100-level courses. In response to the question, "What do you like best about the course?" some typical replies were as follows:
"I liked to be able to decide what experiment to perform."
"The teacher set up the class like it was a real lab and we were real scientists. It gave us freedom and showed us how the scientific process worked."
"I like the experimenting because you never know what the results will be."
On the other hand, in response to the question, "If you were teaching the course, what would you do differently?" two students mentioned that they would have preferred eventually switching to a different model system, suggesting that they had grown weary of pollen.
Other specific observations, from my perspective, were as follows:
* The class made progress in solving the research problem.
During the semester, the class developed an incubation medium that increased the percentage germination from approximately 5% to approximately 55%. This laudable result was achieved by the combination of scientific method, student creativity, instructor guidance, and the collaborative learning that resulted from class discussions. I was very proud of the students' performance.
* The importance of keeping a lab notebook became evident.
At first, most students were reluctant to use the regimented experimental design format because the experiment number, purpose, and materials and methods were 'too obvious" to write down. However, after a few weeks they came to realize how helpful it was to have this information in an organized format.
* Students had difficulty getting beyond "what should have happened."
Students had a particularly difficult time analyzing their data. Because students were so accustomed to figuring out what "should have happened," they found it very difficult to be objective in analyzing experimental results. Eventually, however, they became adept at drawing logical conclusions based on their data alone.
In addition, the concept of statistical significance proved to be easier for students to grasp in the abstract than the concrete. For example, in practice problems involving the interpretation of histograms with SE bars, students were consistently correct in identifying which treatments were significantly different and which were not. However, when analyzing the data they collected from their own experiments, they would frequently make statements such as, "If one ignores the SE bars, the treatments are different, but if the SE bars are included, the treatments are the same." Obviously, such students missed the point that the standard error should always be included in their analyses.
* Preparing solutions was more easily accomplished in theory than in practice.
Preparing solutions was another task which the students performed better in the abstract. On practice problems involving dilutions, I was initially surprised to see that the students performed the calculations properly. However, once they began working on their own experiments, they frequently had difficulty on exactly the same types of calculations.
* Unfortunately, the investigative laboratory method increased the chance that no positive results would be obtained.
Because I had no prior knowledge of which nutrient would work and which would not, I could not shift students away from using treatments that would have no noticeable effect on germination. Although I warned students that most likely they would experience both the "thrill of victory and the agony of defeat," students were understandably discouraged when they worked long and hard on an experiment only to find that zero germination was obtained for all their treatments. My comment that "this is what usually happens in science" did not provide much consolation.
* The lab meeting concept worked particularly well for several reasons.
First, such group discussions minimized competition among the pairs of students because the emphasis was on working as a team with the goal of solving the germination problem. In fact, such meetings, sometimes at lunch, helped build group solidarity. These group interactions seemed especially helpful to students in their first year at college. Second, pooling the class data on the chalkboard proved to be helpful for those students whose experiments resulted in zero germination. Those students could see what other students had found and take heart that a solution might, in fact, he possible. In addition, they could then use this new information to design their next experiment.
From my perspective the course was very successful. The fact that neither I nor my students knew the answer to the problem made the course tremendously exciting, and I thus functioned more as a resource person than as a provider of knowledge. The students soon adapted to doing the research and seemed enthusiastic about venturing into the unknown. Even though each laboratory session was filled with frustration because experiments seldom worked the way the students predicted, they rebounded rapidly from their disappointments and quickly designed a new experiment.
My experience is similar to those of others using I-labs. Namely, introductory students -- even those not majoring in a science -- can excel in and even enjoy a research-based science course. This helps dispel the myth that only upper-level science majors are capable of doing research (Thornton, 1972a).
By the end of the semester, we had not completely solved the pollen germination problem. Pedagogically, this is of no consequence because the course was designed to teach the process of science, and in that regard, I consider it a complete success. Interested readers who wish to try the I-lab system themselves are encouraged to adopt the Gladiolus pollen model system because there is still much work that can be done with it. A time line that includes suggestions for implementing an I-lab course are provided in the Appendix.
For instructors contemplating the I-lab approach, the following is the basic schedule I used in my course, which met once per week for 2.5 hours, along with suggestions for implementation.
APPENDIX: TIME LINE AND SUGGESTIONS
Several months before the course begins:
Decide on the model system to be used.
1. For ideas on systems other than pollen germination, instructors might utilize aspects of their own research or consult with colleagues about possible research options.
2. Ideally, one should have a second project in mind in case student interest wanes on the initial project. For example, one could study the germination of seeds rather than pollen. In particular, one could test the effects of "natural" weed killers, such as corn gluten (www.gluten.iastate.edu), on the germination of seeds from a variety of plant species. Alternatively, one could germinate seeds from two species in the same Petri dish and test for evidence of allelopathy, the growth inhibition of one species caused by the growth of another species (Raven et al., 1999).
3. Whatever method is chosen, it is important to plan follow-up experiments in case students solve the problem on their first attempt. That is, the project must be one that can be on-going and thus capable of being studied over the length of the course. For example, a follow-up to the pollen germination project could be staining the nuclei in pollen tubes (Tatina and Hohn, 1994), measuring their rate of movement down the pollen tube, and determining when mitosis of the generative nucleus occurs.
4. If the project involves instrumentation, either plan to have enough instruments available for each pair of students to use, or develop a plan so that students will not be idle while waiting their turn to use what is available.
5. Determine if a computer lab will be available for classroom instruction in Excel or whatever software package is used for statistical analysis. If necessary, schedule this room well in advance.
At least one week before the first class:
Prepare the necessary handouts, and assemble the necessary supplies and equipment.
1. Take extra care to provide adequate written instructions for using Excel. Ask a colleague or a student to test those instructions to make sure they are clear and correct.
2. Prepare additional written instructions as needed. I prefer to provide numerous handouts to make sure students have an accurate set of instructions for reference throughout the course. I instruct students to tape these instructions into their lab notebooks.
1. Course introduction
2. Distribute and collect a sheet that provides information on each student's background in science and math
3. Distribute and go over a handout dealing with statistical analysis of data. (Because I thought it important to begin the course with a hands-on experience that exemplified "science in action," I decided to focus on data analysis using the computer.)
4. Adjourn to the computer lab for practice in using Excel, and then complete an assignment using Excel to analyze hypothetical data
1. Discuss the previous week's assignment
2. Distribute and discuss a handout on experimental design, according to the model shown in Figure 1
3. Distribute a worksheet that presents some hypothetical observations, and instruct students to divide into groups to formulate an hypothesis, design an experiment to test it, and present their work to the class
4. Distribute another set of hypothetical data for students to analyze using Excel at the computer lab, and instruct them to submit their conclusions by the end of class
1. Discuss the previous week's assignment
2. Distribute and discuss a handout on how to prepare solutions
3. Distribute a sheet of sample problems involving the preparation of solutions, and instruct students to work in groups to verify their understanding of the calculations
4. Give an open-note, open-book quiz on making solutions
5. Distribute another hypothetical experiment to analyze using Excel and submit at the end of class
1. Discuss the previous week's assignment
2. Give a mini-lecture on pollen (including flower structure) and the rationale for using pollen germination as a model system
3. Distribute and discuss a detailed set of procedures for preparing solutions for germinating pollen, obtaining pollen grains from flowers, and inoculating an incubation medium
4. Distribute and discuss a sample experimental plan that involved testing the effectiveness of various supports for pollen during their incubation
5. Instruct students to work in groups to conduct this experiment in order to become familiar with the procedures
1. Give a mini-lecture on how to use the microscope to determine the germination percentage, and instruct the class to use these procedures on the pollen they inoculated the previous week
2. Use Excel to analyze the data
3. Instruct each group to write its numerical results on the board, and use these results to demonstrate and discuss variability
1. Distribute and discuss a handout that provides suggestions for conducting follow-up experiments
2. Instruct students to work in groups to design their own experiments and complete the necessary calculations for preparing the required solutions
Seventh through fourteenth classes:
In general, students work in groups for the remainder of the semester according to the following schedule:
1. During one class, decide on the hypothesis to test, and design the appropriate experiment. Then prepare the experimental media and inoculate with pollen
2. During the next class, determine the percentage germination, analyze the data, and decide on the next experiment
3. Repeat the steps as time permits
"Lab meetings" were held every few weeks to discuss results. Lab notebooks were collected and graded approximately every three weeks.
[FIGURE 2 OMITTED]
Figure 1: A typical format for designing an experiment. Experiment #_____ Purpose: (For example: To test the effect of sucrose concentration on pollen grain germination) Materials and Methods: A. Experimental Plan: Pollen from Gladiolus flowers was "dusted" onto solidified 2% agar solutions containing different concentrations of sucrose as follows: TEST # # OF REPLICATIONS [SUCROSE] (M) 1 3 0 --- (distilled water as a control) 2 3 0.1 3 3 0.2 4 3 0.3 5 3 0.4 6 3 0.5 B. Procedures: (Here students would list the steps in preparing the necessary solutions, inoculating the agar with pollen, and incubating the pollen until the next laboratory period.)
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BREWBAKER, J. L. and B. H. KWACK, 1963. The essential role of calcium ion in pollen germination and pollen tube growth. Amer. J. Bat, 50: 859-865.
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SCHIMPF, D. J. 1992. Rapid germination of pollen in vitro. Amer. Biol. Teacher 54: 168-169.
SUNDBERG, M. D. and G. M. MONCADA. 1994. Creating effective investigative laboratories for undergraduates. Bioscience 44: 698-704.
TATINA, R. and K. HOHN. 1994. A technique for staining pollen nuclei. Amer. Biol. Teacher 56: 174-175.
TAYLOR, L. and P. K. HEPLER. 1997. Pollen germination and tube growth. Ann. Rev. Plant Physiol. 48: 461-491.
THORNTON, John W., ed. 1972a. The Laboratory: A Place to Investigate. Washington, D.C., American Institute of Biological Sciences.
_____. 1972b. An investigative laboratory in cell biology. Pp. 50-54 in Thornton, John W. (ed.). The Laboratory: A Place to Investigate. Washington, D.C., American Institute of Biological Sciences.
TSE, H. L. H. and G. Y. S. CHAN. 2001. Pollen germination -- a challenging and educational experiment. J. Biol. Education 35: 148-151.
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|Author:||Evans, Robert C.|
|Publication:||Bulletin of the New Jersey Academy of Science|
|Date:||Mar 22, 2003|
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