Viruses
Laboratory

Objective
To study the effect of the tobacco mosaic virus on leaves of tobacco plants

Process Skills
hypothesizing, experimenting

Materials
4 tobacco plants, glass-marking pencil, tobacco from several brands of cigarettes, mortar and pestle, 10 mL 0.1 M dibasic potassium phosphate solution, 100-mL beaker, cotton swabs, 400-grit carborundum powder

Background
The tobacco mosaic virus, TMV, infects tobacco as well as other plants.

1 What is a virus?

2 How do viruses enter a host cell?

3 How do viruses exist outside of host cells?

4 Describe how viruses spread among organisms.

Technique
1 Place pinches of tobacco from different brands of cigarettes into a mortar. Add 5 mL of potassium phosphate solution and grind the mixture with a pestle.

2 Pour the mixture into a beaker. This mixture can be used to infect the tobacco plants with

TMV. What does this assume about cigarette tobacco? NOTE: Wash your hands and all laboratory equipment used in this step with soap and water. Why?

3 To apply the mixture to a tobacco leaf, moisten a swab with the mixture and sphnkle a small amount of carborundum powder onto the moistened swab. What is the purpose of the carborundum powder? Apply the mixture to the tobacco leaf by scraping the swab over the surface several times.

Inquiry
1 Discuss the objective of this laboratory with your partners and develop a hypothesis.

2 Design an experiment to test your hypothe515 that uses the setup described above in Technique.

3 What are the independent and dependent variables in your experiment? How will you vary the independent variable? How will you measure changes in the dependent variable?

4 What controls will you include?

5 How will you record your results?

6 Obtain noninfected tobacco plants and proceed with your experiment after receiving approval from your teacher.

Conclusions
1 Do your data support your hypothesis? Explain.

2 What differences, if any, did you detect in the susceptibility of older and younger leaves to the virus?

3 What were some of the possible sources of error in your experiment?

4 Greenhouse operators generally do not allow smoking in their greenhouses. Aside from health and safety issues, how might your results support this rule?

5 What was the purpose of grinding the leaves in Technique, step 1? Why is tobacco from different brands of cigarettes used?

  Further Inquiry

Tobacco Mosaic Virus is capable of infecting different species of plants. Design an experiment to determine which of several types of plants are most susceptible to the virus.