Introduction (written for students):

       This experiment is designed to study biotic/abiotic factors affecting seedling growth. Biotic factors are interactions between the living components of a community (i.e., predation, competition); abiotic factors are those between living organisms and the non living portion of the environment (i.e., pH, wind, water, and solar radiation). To study these factors, we will use genetically bred, 7-day old Rapid cycling Brassica's (RCB's), which have rapid growth to maturity (i.e., approximately 30 days).

       Rapid-cycling Brassica's (RCB's: Brassica rapa L.) were designed for use inside the classroom with adequate lighting provided at all times. However, this project is conducted outdoors, where a variety of environmental factors could have an impact on growth. These include exposure to and intensity of light, insect herbivory, air temperature, competition for light or resources with other plants, etc. There are also many factors that you, the student can manipulate such as fertilization, clipping, and growth inhibitors. You (and a partner) are to formulate an hypothesis and design an experiment to test your hypothesis. (i.e., think about why it is important to measure 1 variable at a time when conducting an experiment). In addition, there are two different types of RCB's to choose from - a dwarf type (rosette) and a wild type. These two types can be used separately or compared against each other. Your assignment is to come up with an hypothesis to test the affect of a biotic and/or abiotic factor in our environment that may affect seedling plant growth in real-life situations, not just for RCB’s. This must be completed during the next two lab periods. An example is: "We hypothesize that seedlings of RCB's located in areas of dense grass will not be shorter after 2 weeks than those in a less dense area.” Or, perhaps you think the number of flowers that your plants produce, or their biomass, would be a better gauge of the growth of these plants. It is up to you to determine what will be appropriate for your experiment. The only stipulation is that your effect must produce measurable data. We will provide instruction in the use of various equipment (light meter, etc.), and will be available for assistance in refining your hypothesis, if necessary. After spending 2 weeks collecting data, you will then write your own scientific paper, using the data collected. It will be due at the beginning of the next lab period.



Materials and Methods (written for faculty):

Study Site(s).

       You will conduct your experiment in a field setting chosen by your instructor. You should notice the heterogeneous plant cover that could be utilized in your experimental design. Hypothesize about which area may have greater levels of wind velocity, solar radiation, predation, or competition. For example, you may compare seedling growth in a shaded area vs. a sunny area to measure the effects of solar radiation on seedling growth.

Overview of Data Collection and Analysis Methods.

Week 1.

       You should come to class ready to begin your experiment. In your work group, you should discuss the hypothesis with the instructor before conducting your experiment. This allows your instructor to determine if your group hypothesis is testable and to guide you to the proper equipment or plant variety best used in your experiment. For example, students that want to investigate the effects of gibberellic acid on their seedlings may not be aware that they will achieve better results with the dwarf variety of Brassica rapa.

       Once your hypothesis is approved by your instructor, the experiment needs to be set up and baseline "before" measurements should be taken. For example, many students measure the height of the plant, the length of the longest leaf, and count the number of leaves. After these measurements, you should subject your plants to the specified treatment (example: applying 3 sprays of gibberellic acid solution to the plants). Then place your plants in their pots on the ground in a predetermined area. You should water your plants. Place a flag next to them with your name and the treatments you used written on it with a magic marker. A laboratory supervisor or student worker will maintain the plants throughout the week because the study site is a considerable distance away from the university (approx. 15 miles). The plants will be watered daily. If you would like additional applications of a substance applied to your plants by the laboratory supervisor, affix a piece of flagging tape to your flag with detailed instructions.

Week 2.

       During the second week of lab you will collect "after" data from the plants and remove your experiment from the field site. You will use this data to write a scientific paper which will be due the next class period. The scientific paper should include an abstract, introduction, materials and methods, results, discussion, and references section. The structure of your paper should be based on the guidelines in Appendix A of the lab book Investigating Biology by Morgan and Carter, 1999.



Questions for Further Thought and Discussion:

  1. What abiotic and biotic factors can affect seedling growth?

  2. How do different abiotic and biotic factors affect seedling growth?

  3. What constitutes a testable hypothesis?

  4. What is the value and/or limitation of field experiments?

  5. How does scientific research help us understand better the natural world?

  6. Why are native ecosystems useful for ecological research?

  7. What is a control and why is it important?

  8. Why is it difficult to measure more than one variable simultaneously?

*** Note: Answers to many of these questions and numerous other comments by the contributing author can be found in the "NOTES TO FACULTY" page.



References and Links:



Tools for Assessment of Student Learning Outcomes:

       Guidelines for assessment: The grading scheme for the scientific paper was based on 80 possible points. We used a 5 point scale for each major category: 0 = no evidence, 1 = little evidence, 2 = evident, lacking minor aspects, 3 = some evidence, adequate for project, 4 = good evidence, helping the project, and 5 = excellent. This 1-5 scale was scaled to the point value of each main category.

The oral in-class presentation was worth 20 possible points.



Tools for Formative Evaluation of this Experiment:

       We asked the students to write hypotheses/finish sentence stem before and after the intervention. Before the lab sequence we asked the students to following related to the Brassica experiment:

       * We then lead the students down the “succession trail” which is maintained to demonstrate the various stages of plant succession.

       * After the labs, we ask the students to answer the same questions again.

       * Peer-review of another student’s hypothesis using a grading rubric will facilitate a better understanding of hypothesis development.

An extensive discussion on Evaluation appears in the Teaching section of this site.