Project-based learning (PBL) and traditional teaching methods represent two opposing pedagogical philosophies. A PBL Biology lab course was designed and taught concurrently with its traditional counterpart to compare student success. The PBL course investigated the effects of simulated acid rain on the rate of adaptation in two species that differ in complexity and rate of reproduction, Caenorhabditis elegans and Paramecium caudatum. The species with the highest number of survivors at the end of six week's exposure to acid rain was deemed to have adapted best. In two out of three semesters students concluded that P. caudatum responded to acid rain with the greatest rate of adaptation. Student success was compared between both types of courses using four methods of assessment: student academic performance, retention rate, transfer rate to four-year institutions, and participation points. The results of two methods of assessment out of four were statistically significantly higher in the PBL courses. Considering that the other two methods of assessment did not favor traditional pedagogy, but produced comparable student success in the traditional and PBL courses, it can be concluded that PBL pedagogy is a highly desirable alternative to traditional teaching methods in biology courses at the community college level.

Introduction

Course Description

PBL Biology 122 is a five-credit lab course designed for biology, health, and education majors. It provides an introduction to the structure and function of major groups of organisms and stresses evolutionary relationships and ecological principles. Only students who pass a designated general biology course with a grade of C or better or have the consent of the biology department chairperson are allowed to enroll in the course. The course is offered every semester, meeting for three hours twice a week. It includes a four-hour lecture and a two-hour lab per week, taught by the same instructor. The course is usually in demand because it is transferable to a four-year college. The course was redesigned into both PBL and traditional formats in order to use the PBL format to address the fundamental challenge of increasing student motivation, mastery of course material, and application of learning to real-world situations.

Course Design

A ten-week experiment was designed that replaced the lab portion of the existing traditional Biology 122 course with a PBL lab. The experiment exposed two organisms of different complexity to simulated acid rain and compared their adaptation rates. The traditional and PBL courses were taught concurrently for three consecutive semesters, each by the same instructor.

In a typical PBL course students are presented with a research question, do background research, construct a hypothesis, and test it with a long-term experiment. In contrast, traditional students conduct labs that complement lecture material, but are disjointed and lack a common theme of inquiry. Also, whereas PBL students use their judgment to evaluate real-world experimental data and overcome obstacles (Movahedzadeh et al., 2012; Fox, 2013; Movahedzadeh et al., 2015; Cherif et al., 2014; Doles, 2012; Sahin & Yorek, 2009), traditional students rotely follow directions from a lab manual, and routinely answer questions by summarizing the lab's background information.

Methodology and Procedures

A study was conducted for three semesters of Introductory Organismal Biology to compare student success in traditional versus PBL courses. The two courses had identical lecture curricula, but different labs. Unlike the traditional labs, the PBL labs included a ten-week experiment that compared the rate of adaptation to simulated acid rain between C. elegans and P. caudatum. These were chosen for the experiment because they are easy to culture, inexpensive, and well-documented. Before starting the experiment, students were divided into groups and read instructor-generated information relating to C. elegans, P. caudatum, and acid rain, and learned that both C. elegans (Hodgkin & Barnes, 1991) and P. caudatum produce a large number of offspring, but that P. caudatum has a greater rate of reproduction. (Karino & Hiwatashi, 1982). Students also conducted an online research review to find studies that compared adaptability between complex and simple forms of life, and found that the existence of an evolutionary trend toward complexity is still debated among scientists. Then a hypothesis was formulated that addressed the question, “Do Paramecium caudatum and Caenorhabditis elegans respond to acid rain with the same rate of adaptation?” To formulate the hypothesis, students had to compare the rate of adaptation of the more complex, 1000-celled C. elegans to the rate of adaptation of the less complex, unicellular P. caudatum. Students first considered that, according to the Principle of Relative Fitness, the fittest and therefore more adaptable organisms have the greatest rate of reproduction. Second, they considered that, according to an evolutionary trend toward complexity, the most complex forms of life are able to use resources more efficiently and adapt best. Lastly, students juxtaposed the competing notions of complexity and rate of reproduction, and evaluated their influence on adaptability. Some students hypothesized that the more complex and efficient C. elegans would adapt best; other students assumed that the more plentifully reproducing P. caudatum would adapt best.

During the following three weeks of the experiment, students prepared Escherichia coli N2 broth cultures, streaked NGA (nematode growth agar) plates with E. coli N2 (the source of food for C. elegans) and prepared an experimental and control culture of both C. elegans and P. caudatum. Both experimental cultures were exposed to acid rain during week 4, and although C. elegans has a larger mass than P. caudatum, the two species were exposed to the same concentration of simulated acid rain because in nature they live in close proximity in ponds and would therefore receive equal exposure to acid rain. (Viz. P. caudatum was exposed to 200 μl of simulated acid rain per 25ml of culture solution, and C. elegans was exposed to 200 μl of acid rain per 20 ml of NGA.) During week 5 the concentration of simulated acid rain was increased to 1 mL, and continued to be increased by 1 mL each week until week 9 when 5 mL of acid rain were administered. The number of survivors in both the C. elegans and P. caudatum cultures were counted and recorded weekly from week 4 to week 10, and during week 10 a final count for each species was taken. More specifically, the number of Paramecia per milliliter of culture solution and the number of C. elegans per Petri dish were counted.

To count the Paramecia, drops of 0.5 ml of culture were released on a glass plate, and if more than 8–10 per drop were counted, then a serial dilution was performed. Likewise, following Theresa Stiernagle's methodology for the maintenance of C. elegans (Stiernagle, 2006), if more than forty worms were counted in a dish, then a wedge of agar with 2–3 worms was transferred to a new NGA plate to be used for the remainder of the semester or until it housed a number of worms greater than forty.

During weeks 5, 6, and 7, growth in both cultures, barring episodes of culture contamination, typically was high and it was not possible to determine which species produced the greatest number of survivors. However, during weeks 8, 9, and 10, growth diminished in both species and a comparison was possible. During week 10 each group of students calculated the percentage growth difference between the first and last weeks of exposure to simulated acid rain in both the experimental and control cultures of the two species. More specifically, students calculated the percentage growth difference between the experimental C. elegans and experimental P. caudatum cultures, and deemed that the culture with the greater percentage growth difference was the one with the greatest rate of adaptation. In the control culture the number of organisms for each species remained high, as was expected. On week 10 students drew a data table on the class board, and each lab group listed the number of organisms in the two species for both the experimental and control cultures. The instructor also asked one person per lab group to share with the class insights they had gained throughout the experiment.

Each group of students submitted to the instructor a weekly lab report that included a data table reporting the number of organisms counted for both the experimental and control cultures of each species, the amount of simulated acid rain administered, and the room temperature. The weekly lab report also included a section where students discussed the weekly effect of simulated acid rain on the growth of both C. elegans and P. caudatum, and commented on improvements to be made to their technique. In week 10, a comprehensive lab report was submitted that comprised all the sections of the research study. Both reports were graded and became part of each student's final grade for the course.

To avoid contamination when administering simulated acid rain, students used aseptic techniques and opened the NGA plates and the P. caudatum jars only under a laminar UV flow hood. The experiment was repeated for three semesters, and in two semesters out of three the number of P. caudatum was higher, leading students to conclude that P. caudatum has the higher rate of adaptation to simulated acid rain. However, additional trials should attempt to resolve the persistent problem of contamination in both the P. caudatum and C. elegans cultures before this preliminary result can be analyzed.

Assessing Student Success

Assessment is an important part of the teaching process because it allows faculty to measure students’ learning as well as to gauge the improvement of teaching, curriculum, and conditions for student learning. In this study, the four methods of assessment used to compare student success in the two courses were academic performance, student retention rates, transfer rates to a four-year institution, and participation points. Retention rates were calculated by counting the number of students who completed the courses; transfer rates were provided by the Research and Planning office at the Community College where the study was conducted; and participation points were tallied by counting the points each student gained during designated class activities. In both the traditional and PBL courses the following protocol was followed to assess student success:

  • The same course curriculum was taught in the lecture portion of both the traditional and PBL courses; the lab portion was different.

  • Final student grades were compared between the traditional and PBL courses.

  • Student retention was compared in both the traditional and PBL courses.

  • Student transfer rate to a four-year institution was compared between the traditional and PBL courses.

  • Student semester participation points were compared between the traditional and PBL courses.

Each student's final grade for both the traditional and PBL courses included tests, lab work, assignments, class presentation, and participation. Student retention was measured by calculating the number of students who completed the course for a grade; students who earned a grade of A, B, C, and D were deemed to have completed the course successfully. Student participation points were calculated by counting the number of points students gained for contributing to instructor-designated classroom activities. Table 1 summarizes the methods of assessment and how they were used to evaluate the traditional and PBL forms of delivery.

Table 1.
Methods of assessment used to evaluate the traditional and PBL forms of learning.
Methods of assessmentExplanation
1 Academic performance The means of the total points all traditional students earned cumulatively over the course of three semesters were compared to the means of the total points all PBL students earned cumulatively over the course of the same semesters. 
2 Student retention rate Student retention was calculated by counting and comparing in each of the two courses the number of withdrawn, retained, and total students (withdrawn plus retained) cumulatively over the course of three semesters. 
3 Student transfer rate Transfer rate was measured by counting and comparing in each of the two courses the number of transfer, non-transfer, and total students cumulatively over the course of three semesters. 
4 Student participation points Student participation points were calculated by counting and comparing in each of the two courses the number of participation points students received cumulatively over the course of three semesters. 
Methods of assessmentExplanation
1 Academic performance The means of the total points all traditional students earned cumulatively over the course of three semesters were compared to the means of the total points all PBL students earned cumulatively over the course of the same semesters. 
2 Student retention rate Student retention was calculated by counting and comparing in each of the two courses the number of withdrawn, retained, and total students (withdrawn plus retained) cumulatively over the course of three semesters. 
3 Student transfer rate Transfer rate was measured by counting and comparing in each of the two courses the number of transfer, non-transfer, and total students cumulatively over the course of three semesters. 
4 Student participation points Student participation points were calculated by counting and comparing in each of the two courses the number of participation points students received cumulatively over the course of three semesters. 

Results and Discussion

Academic Performance

The number of points earned on classroom exams, lab work, assignments, class presentation, and participation were added for each traditional and PBL student, and corresponded to the final semester grade. The total number of points students could earn in a semester was 1000. Academic performance was calculated by performing an independent-samples t-test that compared the means of the total points all traditional students earned cumulatively over the course of three semesters (Spring 2014, Fall 2014, and Spring 2015) to the means of the total points all PBL students earned cumulatively over the course of the same semesters. Table 2 reports the means of the total points for both traditional and PBL students, the standard deviation for the distribution of sample means, and the total number of both traditional and PBL students. The results of the independent-samples t-test are also reported in Table 2 and indicate that there was no significant difference in academic performance of traditional (M = 788.91, SD = 78.21) and PBL (M = 807.25, SD = 64.10) students.

Table 2.
Academic performance: means of student total semester points for the Spring 2014, Fall 2014, and Spring 2015 semesters (t104 = −1.368, p = 0.1742).
TraditionalPBL
788.91 807.25 Mean = −18.341 difference (Traditional – PBL) 
78.21 64.10 SD = 13.405, hypothesized difference = 0 
N = 55 N = 60  
TraditionalPBL
788.91 807.25 Mean = −18.341 difference (Traditional – PBL) 
78.21 64.10 SD = 13.405, hypothesized difference = 0 
N = 55 N = 60  

Student Retention Rates

Student retention rates were calculated over the course of three semesters by counting the number of students who officially withdrew from the course, and subtracting them from the total count of students who received a grade of A, B, C, D, or F. The students who failed the courses were included in the number of retained students. Table 3 divides both the traditional and PBL students into three categories—withdrawn, retained, and total students (withdrawn plus retained)—and uses the observed and expected students of each one of these categories to calculate the reported chi-square values. Retention rates were cumulatively analyzed for statistical significance over the course of three semesters from Spring 2014 to Spring 2015, and were not found to be statistically significantly higher for the PBL course. The results of the test for statistical significance of retention rates are reported in Table 3. No significant difference in participation points was found (χ2 (1) = 0.83, p = 0.362). There is insufficient evidence to support the claim that class retention rates would be greater under the PBL instruction treatment than under the traditional treatment.

Table 3.
Retention rates for the Spring 2014, Fall 2014, and Spring 2015 semesters (χ2 = 0.83, df = 1, p = 0.3617).
TraditionalPBLTotal
Withdrawn Observed
Expected
% of χ2 
22
19.50
38.5% 
17
19.50
38.5% 
39
39.00
77.1% 
Retained Observed
Expected
% of χ2 
63
65.50
11.5% 
68
65.50
11.5% 
131
131.00
22.9% 
Total Observed
Expected
% of χ2 
85
85.00
50.0% 
85
85.00
50.0% 
170
170.00
100.0% 
TraditionalPBLTotal
Withdrawn Observed
Expected
% of χ2 
22
19.50
38.5% 
17
19.50
38.5% 
39
39.00
77.1% 
Retained Observed
Expected
% of χ2 
63
65.50
11.5% 
68
65.50
11.5% 
131
131.00
22.9% 
Total Observed
Expected
% of χ2 
85
85.00
50.0% 
85
85.00
50.0% 
170
170.00
100.0% 

Student Transfer Rate

Generally, the measures of community college students’ success have been measured by the starting point (enrollment) and the ending point (completion of AAS degree or transfer to a four-year college) of their college experience. An institution's effectiveness or success is often measured by a student's likelihood of completing a postsecondary credential or transferring to a four-year college. As a result, community colleges attempt to ensure that their students are prepared to transfer to a four-year college, or that they become career-ready and prepared to pursue their life goals. Indeed, the rate of student transfer to a four-year college has been used as one of the parameters for measuring the institutional effectiveness and the success of two-year colleges. For example, a research team from the Community College Research Center (CCRC) at the Teachers College of Columbia University concluded that community college students who transfer to a four-year institution being academically unprepared continue to lag substantially behind their more prepared counterparts (Bailey et al., 2005). Because of the significance of transfer rates to a baccalaureate institution, they were included as a metric of comparing the success of PBL and traditional Biology 122 courses. The transfer rates reported in Table 4 account for students who transferred to a four-year institution with or without having completed an Associate of Applied Science Degree.

Table 4.
Transfer rates for the Spring 2014, Fall 2014, and Spring 2015 semesters (χ2 = 5.75, df = 1, p = 0.0165; significant at α = 0.05).
PBLTraditionalTotal
Transfer Observed
Expected 
38
30.50 
23
30.50 
61
61.00 
Not Transfer Observed
Expected 
47
54.50 
62
54.50 
109
109.00 
Total Observed
Expected 
85
85.00 
85
85.00 
170
170.00 
PBLTraditionalTotal
Transfer Observed
Expected 
38
30.50 
23
30.50 
61
61.00 
Not Transfer Observed
Expected 
47
54.50 
62
54.50 
109
109.00 
Total Observed
Expected 
85
85.00 
85
85.00 
170
170.00 

A chi-square test of independence was calculated, comparing students’ transfer rates between the traditional and the PBL instruction groups cumulatively over the course of three semesters from Spring 2014 to Spring 2015. Table 4 indicates that both traditional and PBL students were ranked in three categories—transfer, non-transfer, and total students—and each category was divided in two subcategories, observed and expected students. The number of observed and expected students falling into each subcategory for the traditional and PBL instructional groups are reported in Table 4 and were used to calculate the chi-square values also reported in Table 4. The results of the chi-square test of independence are reported in Table 4. A significant difference in transfer rates was found (χ2 (1) = 5.75, p = 0.017). There is sufficient evidence to support the claim that the number of transfer students from the traditional instruction group is less than the number of transfer students from the PBL group.

Student Participation Points

The total number of participation points students can earn during an academic semester is 50. Students earn one participation point each time they contribute to class discussions, help a classmate, or ensure that all members in their lab group contribute their work. Students also lose a point each time they arrive late to class, leave early, or do something that is not what the class is doing. The total number of class discussions and group activities in an academic semester is 29. During class discussions the instructor strives to distribute points equally among students by preventing any student from dominating discussions and accruing more points. Students add up their participation points on an instructor-generated chart. Both the instructor and students keep a tally of participation points. Once a month the instructor verifies that students are adding up participation points correctly. At the end of the academic semester students submit their number of participation points to the instructor. A chi-square test of independence was calculated comparing students’ participation points between the traditional and the PBL instruction groups over the course of three semesters from Spring 2014 to Spring 2015. Participation points were ranked in three categories, from poor (0–33) to fair (34–42) to good (43–50), and the number of students falling in each category for the traditional and PBL treatments were counted. Table 5 reports the number of participation points both traditional and PBL students gained in each of the three subcategories. A significant difference in participation points was found (χ2 (2) = 8.32, p < 0.05). The number of participation points earned by the traditional instruction group is less than the number of participation points earned by the PBL group.

Table 5.
Participation points for the Spring 2014, Fall 2014, and Spring 2015 semesters (χ2 = 8.32, df = 2, p = 0.0156).
TraditionalPBLTotal
Poor
0–33 
Observed
Expected 
8
6.73 
6
7.27 
14
14.00 
Fair
34–42 
Observed
Expected 
28
21.16 
16
22.84 
44
44.00 
Good
43–50 
Observed
Expected 
27
35.11 
46
37.89 
73
73.00 
Total Observed
Expected 
63
63.00 
68
68.00 
131
131.00 
TraditionalPBLTotal
Poor
0–33 
Observed
Expected 
8
6.73 
6
7.27 
14
14.00 
Fair
34–42 
Observed
Expected 
28
21.16 
16
22.84 
44
44.00 
Good
43–50 
Observed
Expected 
27
35.11 
46
37.89 
73
73.00 
Total Observed
Expected 
63
63.00 
68
68.00 
131
131.00 

Conclusion

Academic performance, student retention rates, transfer rates, and participation points are four key metrics educators use to measure student success. PBL students scored statistically significantly higher for two of these metrics during the three semesters examined. The other two metrics examined show no statistical significance to favor or disfavor PBL courses. In conclusion, the statistically significant results obtained in favor of the PBL pedagogy are a sufficient indication that PBL pedagogy promotes student learning gains.

We would like to thank Fredrick Berchiolli for editing several drafts of this study; Dr. Junoo Tuladhar, who prepared all labs for both the PBL and traditional courses; and Mr. William Thompson, who prepared some of the labs for the traditional course.

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