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Laboratory Exercises in Plant Science: Germination and Environment
Many variables in the environment surrounding germinating seeds have important effects on germination and seedling development. In fact, a number of conditions have to exist within a fairly narrow range to achieve successful germination. Many of the treatments students develop will probably have very negative effects on germination compared to controls. These negative responses can be quite dramatic and exciting to the students.
The brainstorming by our students resulted in many imaginative ideas. Many ideas seemed "silly" and were outside the do-able limitation, but these too were valuable starting points. Proposed ideas for an experiment on drug effects on seeds became a test of aspirin in the germination water; an experiment on alcohol effects became a test of cola in the germination water; and a test of winter survival became an experiment on the effect of seed storage in a freezer before the germination test. The concept of keeping it doable by studying only one or two variables within the allotted time frame of a couple of weeks is an important challenge to students.
The "do-able" issue confronts scientists in virtually every experiment they design. The students also need to consider the nature of the control, and what actually is the control for the specific treatment being investigated.
The outcomes of the various experiments are truly unknowns. Because of the nature of these student experiments, many are likely to have never been performed. The students must use their own minds in obtaining the results and in developing their own conclusions. Probably, the teacher's role is to probe the students with questions about alternative conclusions, the implications of their experiment in view of their original hypothesis, and importantly, ideas for improving or repeating the experiment. Remember: Some of the most significant knowledge in science is gained when things go "wrong"!
1. Begin the exercise with a class discussion. Point out that, up until now, their findings have been observations. Now, based on their previous observations, they can do hypothesis testing. Have them brainstorm environmental factors that might affect germination (e.g., soak/no soak, light/no light, hot/cold, etc.). Discuss general considerations such as accurate measurements, intervention of weekends, controls, and duration of experiments. Remind them to ask themselves, "Is it do-able?"
2. After discussion, the lab groups meet to choose and design their experiments. No variable need be rejected unless it is dangerous, expensive, or otherwise impossible. Groups should consider each idea in terms of control vs. treatment, how the treatment will be done, and what will be measured as well as when and how. It is likely seeds from only a single species need be tested per lab group. The groups should keep in mind that they will be responsible for providing materials not available in the classroom (such as oil, tabasco sauce, or hair spray). Once the decision is made, each group should formulate a hypothesis, agree on materials and methods, and record these in each individual's lab notebook.
3. After allowing a few days for finalizing experiments and organizing materials, lab groups will set up their experiments and make initial observations. Germination progress will be measured over time, according to the design of the experiments.
4. When the experiments are finished, groups will organize data and draw conclusions. This is a good opportunity to practice oral reporting of the studies as well as recording written conclusions discussed in their lab books.
(Group's choice of variable) and Germination
1. What have we learned?
2. Why do we have a control?
3. What is a variable?
4. How many variables can you/should you test in one experiment?
5. What are we considering when we ask, "Is it do-able?"
6. Is it possible to write too much in your lab notebook?
7. What is the difference between a final presentation and the lab notebook?
8. React to the statement, "No one has ever done the same experiment my group has just finished."
9. Is an experiment "gone wrong" a waste of time and material?
1. Did the experiment indicate other factors that need to be included? Does an alternate control need to be tested?
2. Many ideas could likely be expanded into a "dose response" study. That is, try several different levels of the treatment.
3. Are there combined treatments that might interact to affect germination?