Part C

Response to Stimuli

11. Transfer another hydra to the well on your slide, and examine it with the high-power setting of the stereo-microscope. Using forceps, move the long tip of a pennant-shaped piece of filter paper near the hydra's tentacles. Be careful not to touch the hydra with the filter paper. Observe the hydra's response to the filter paper, and record your observations in your data table.

12. Now observe how the hydra responds to a chemical stimulus. Dip the same piece of filter paper in beef broth, and repeat the procedure in step 11. Again, be careful not to touch the hydra. Record the hydra's response to the beef broth in your data table.

13. Finally, investigate how the hydra responds to touch. Using the long tip of a clean pennant-shaped piece of filter paper, touch the hydra's tentacles, mouth, and body stalk. CAUTION Touch the hydra gently. Record your observations in your data table.

14. Transfer the hydra to the culture dish ^W labeled "Used hydras." Clean up your materials and wash your hands before leaving the lab.

Analysis and Conclusions

1. Is vinegar a normal part of a hydra's diet? Why do you think vinegar is used in this step?

2. Based on your observations, how do you think a hydra behaves when it is threatened in its natural habitat?

3. Describe a hydra's feeding behavior.

4. What happens to food that has not been digested by a hydra?

5. What was the purpose of using the clean filter paper in step 11?

6. Did the hydra show a feeding response or a defensive response to the beef broth? Explain.

7. How is a hydra adapted to a sessile lifestyle?

8. How is the feeding method of a hydra different from that of a sponge?

9. Do you think the hydra's response is triggered by water vibrations, by chemicals that daphnia releases, or by daphnia touching the hydra?

Further Inquiry

Design an experiment to determine how hydras respond to other stimuli, such as light.

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