Importance of Tropism

****IF ABSENT – READ THROUGH THE LAB PROCEDURES TO COMPLETE THE PREDICTION SECTION AND THEN ASK A GROUP MEMBER TO HELP YOU WITH NUMBER 4, WE WILL FINISH THE LAB ON FRIDAY*****

Background Information: can change their growth in response to their environment. These changes are called tropisms. Plants can exhibit the following kinds of tropisms:  – the way a grows or bends in response to – the way a plant grows or bends in response to gravity  – the way a plant grows or bends in response to – the way a plant grows or bends in response to touch Tropic responses can be positive or negative. A positive response is when the plant moves toward or in the direction of the . A negative response is when a plant moves away from the stimulus.

Procedures:

1. Take the four corn seeds and place them flat in the bottom of the petri dish with the seeds’ pointed ends facing inward. (Think of them as “hands on a clock” at 12, 3, 6, and 9) 2. Cut a piece of filter paper so that it just fits in the petri dish. 3. Place the filter paper into the petri dish covering the seeds. (be careful not to disturb the position of the seeds) 4. Pour 15 milliliters of tap water on the filter paper. 5. Place enough cotton balls over the filter paper so that when the cover of the petri dish is put on, the paper and the seeds will not be able to move. 6. Place the cover on the petri dish and tape it shut. 7. Turn the petri dish over. You should be able to see the seeds in the bottom on the dish, in the same position they were originally placed. 8. With the vis-à-vis, write the name of your group on the side of the petri dish. 9. Tape the petri dish to the wall of a cupboard, with the bottom of the dish (showing the seeds) facing out. 10. Close the cupboard door so that no light is exposed to the seeds for the next few days. 11. After at least 2 days take the petri dishes out of the cupboard and observe the results.

Predictions:

1. What is the independent variable in this experiment? (think about what is different about the seeds)

2. What is the dependent variable?

3. Write a hypothesis to predict what you think will happen with the root growth of the corn seeds. (must be if/then/because)

4. Draw a picture of the petri dish showing your prediction.

5. Which type of tropism do you think you are testing in this experiment? Conclusion:

1. Write a paragraph summarizing the results of the experiment.

2. Did the root growth match the predicted sketch? 3. What do these results show about how roots grow?

Extension Questions: (you may use your book for help)

1. How does the response of a root to gravity help a plant?

2. Consider plant roots and stems. Explain which tropisms affect both of these plant organs. (consider both positive and negative tropic responses)

3. Do flowers change the way they grow depending on where the light is? If so, how does this help the plant survive?

4. What do you think would happen if you place a light source below the plant? How would the stem grow?

5. Which do you think has a stronger influence on a plant – geotropism or phototropism?

6. How could you design an experiment to test the answer to #5? (write a paragraph describing your experiment)