What's Wrong with the Plants?
Activity 2 (Optional)
The first step of the next activity is for students to work in their teams to create
three different hypotheses regarding what is causing the unhealthy plants. Generally speaking, the two major parts of the plant that they will be investigating are the leaves and the roots, depending on the results of their preliminary observations. Possible proposed hypotheses might be;
"The masses on the roots are destroying the roots."
Have a class discussion where students share their hypotheses. List as many as possible on the board. Students may use their own hypotheses or they may chose one on the board. At this point, each team needs to select a hypothesis they want to test and work together to design an experiment. Before they can begin their experiments they need to have a mini-conference with you to explain their plan and receive approval for the equipment they request. If students are having difficulty, guide their thinking but let them work out a testable plan. Let students identify controls and variables. It is possible that some students may conduct faulty experiments but allow them to find that out for themselves. This is a great source of learning the scientific process.
For best results, have students do their experiments with seedling plants that are about 4" tall. If they inoculate the seeds the plants may not be able to take root and they wont have good experimental data. But, if they insist and can support their rationale, let them give it a try. If students plan to look at roots during various intervals during the experiment, remind them they will need more than one experimental plant. It has been recommended that each plant be inoculated with about 50,000 eggs. This can be determined by using a cell counting slide and dilution formulas, similar to what is done to determine blood cell count.
Possible experimental designs might include;
Take pieces of infected roots and plant near roots of seedling plant.
Inoculate seedlings with eggs in water.
Take soil of infected plants and place on soil of seedling plant.
Soak or grind leaves and place solution on seedling plant.
You need to decide how often and how much time you will allow for students to record data as the plants grow and reveal symptoms. I suggest no more than 5 minutes of class time 3 times a week. If they need more time they could come in at lunch, after school, etc.
The "Laboratory Performance Assessment" should be used as you observe students performing their experiments. There is a "Laboratory Performance Class Evaluation" form for the teacher to use as s/he observes the students perform their experiments and a "Student Grade Sheet" for each students grade and feedback. The lab report will be turned in after all the experiments are over and you have had a Post- Lab Discussion.
The University of Arizona
Department of Biochemistry and Molecular Biophysics
General Biology Program for Secondary Teachers