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Setting Up the Experiment

Put on a lab apron, gloves, and goggles before beginning this investigation.

2. Obtain two tobacco plants that have not been infected with TMV. Label one of the plants "control plant." Label the other plant "experimental plant."

3. CAUTION Use poisonous chemicals ^^ ^^ with extreme caution. Keep your hands away from your face when handling plants or chemical mixtures. Place pinches of tobacco from different brands of cigarettes into a mortar. Add 5 mL of dibasic potassium phosphate solution, and grind the mixture with a pestle as shown in the figure at left.

4. Pour the mixture into a labeled beaker. This mixture can be used to test whether cigarette tobacco can infect plants with TMV.

^Wash your hands and all laboratory equipment used in the previous steps with soap and water to avoid the accidental spread of the virus.

6. Moisten a sterile cotton swab with the mixture, and sprinkle a small amount of carborundum powder onto the moistened swab. Apply the mixture to two leaves on the "experimental" plant by swabbing the surface of the leaves several times. Why do you think swabbing the leaves with carborundum powder might facilitate infection?

7. Moisten a clean swab with dibasic potassium phosphate solution, and sprinkle a small amount of carborundum powder onto the moistened swab. This swab should not come into contact with the mixture of cigarette tobacco. Swab over the surface of two leaves on the control plant several times.

8. Do not allow the control plants to touch the experimental plants. Keep both plants away from other plants that may be in your investigation area, such as house-plants or garden plants. Wash your hands after handling each plant to avoid the accidental spread of TMV.

9. Treat both plants in precisely the same manner. The only difference between the two plants should be the experimental factor—exposure to cigarette tobacco. Both plants should receive the same amount of light and water.

10.^ iJ^ Clean up your materials according to your ^W teacher's instructions and wash your hands before leaving the lab.

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