- Students learn about the diversity of plant viruses by studying their characteristics.
- Students develop a dichotomous key to classify plant viruses.
- Students classify plant viruses.
Activity Materials and Methods:
- Divide students in groups of three or four.
- Provide a card set to each student group.
- Have students read the information on each card and develop a dichotomous key by posing questions about the characteristics of plant viruses.
- Using the dichotomous key, have students classify the plant viruses of the card set.
The lesson starts with a whole-class discussion of the purpose and methods of classification and addressing the notion of a dichotomous key. After the whole-class discussion, students work in groups of three or four, and each group receives a Plant Virus Card Set containing information on 16 plant viruses. Students develop a dichotomous key for plant viruses using the underlined information included in the card set. Students can use the template provided for the dichotomous key (see later in this lesson). The illustrated cards, organized according to dichotomous criteria, serve as a visual organizer, guiding students to think about common traits of different viruses. After all the groups have completed their classifications of plant viruses, the whole-class reflects on the classification process and answers the Study Questions (see later in this lesson), applying the concepts of classifying viruses and using a dichotomous key.
This lesson is to be conducted in a period of 70 minutes. The introductory whole-class discussion will take 10 minutes, the student group work (including development of the dichotomous key and classification) will take 35 minutes, and the whole-class reflection and closure discussion of the Study Questions will take 25 minutes. The cards and template are provided in the Supplemental Information section (see later in this lesson), and the lesson preparation requires printing the template for the dichotomous key and printing out and cutting apart the Plant Virus Card Set.
- Describe the types of genomes you observed in your plant virus sample (card set).
- Describe the plant virus particle shapes you observed in your plant virus sample (card set).
- Describe the disease symptoms produced by the plant viruses you observed in your plant virus sample (card set).
- What is a dichotomous key?
- What is the purpose of a dichotomous key?
- Why do you think scientists classify organisms?
- Suppose that you receive in your lab several small tomatoes with ringspots. Based on your dichotomous key, which virus may be causing this symptom on tomato fruit? Provide details about this virus based on the card information.
- Suppose a farmer sends you a plant with an unknown plant virus. Using an electron microscope, you see that the virus particles have a helical shape. Based on your dichotomous key, what type or types of genomes (e.g., ssRNA+, dsDNA, etc.) could the virus have?
Answers to the study questions can be found in the restricted instructor page.