What's Wrong with the Plants?
Have students work in teams of two or three. It may be good to group them by critical thinking ability having various thinking abilities together. Introduce the first activity by displaying two plants; a healthy one and one that has been infected with the root-knot nematode. Tell students you have been growing these plants exactly the same and you dont know what is causing these symptoms. Have students share what they observe on both plants. List these under the title "Observations" on the board. Then ask students what they would look for on the plant to determine what is causing the unhealthy plant. These should also be written on the board under "Possible Causes". Possible answers might be:
Spots on the leaves
Guide students toward recognizing that they need to observe the aboveground and underground structures as well as the soil in which the plants are growing. The Agrios "Plant Pathology", or any other plant pathology or horticulture books should be available for students to identify symptoms. The student guide should be handed out and students should be guided to use the techniques described and any other ideas of their own to try to determine what is causing the unhealthy plant. Make sure students write all their observations on the attached form. When they have completed their investigations, come together as a class and discuss their ideas. Many students should observe the thickened, galled roots, and the eggs and nematodes in the soil. If students have ideas other than the roots, make sure they have enough evidence to support their causal observations. Guide the discussion in a manner that helps students that may have difficulty recognizing causal relationships. By the end of the discussion most students should have enough information to be able to propose a hypothesis and design an experiment to find the cause of the plant symptoms. They should not consider environmental factors because all plants were exposed to the same factors. The "Laboratory Performance Assessment" should be used during this activity.
If this is the only activity students will be conducting they can propose a hypothesis and design an experiment they would perform if they were to continue. A lab form is provided.
The University of Arizona
Department of Biochemistry and Molecular Biophysics
General Biology Program for Secondary Teachers