Lab: Observing a Hydra
Background Information: The hydra is very thin-only
two cells thick at any point of its body wall. Hydra
live in water because of their thinness, their body
structures tend to lack sophisticated systems.
1. The hydra is in which phylum of the Kingdom
Animalia?
2. Besides the hydra, what are other examples of
animals in this phylum?
3. The animals in the Phylum Porifera are known for their pores. What features are the
animals in this phylum known for?
Objective: to investigate the features and behaviors of a hydra.
Respect for Living Organisms: Please remember that the hydras in this lab are living animals.
When performing labs with live specimens, be sure to handle them correctly to avoid
unnecessary suffering of the specimen.
Materials and Methods: dropper, hydra culture, depression slide, paper clip, daphnia culture,
microscope.
1. Obtain a depression slide and make sure the indentation is on the top surface. Use the
dropper (cut so the opening is wider) to place one hydra and a drop of culture water into
the depression, but do not use a cover slip.
2. Without using a microscope, observe the following: The color of the hydra, the
estimated size of the hydra, the number of tentacles it has, description of its body
shape, prediction of why focusing the microscope on the hydra will be challenging. Record
this information in the data section of your lab.
3. Lightly tap the side of the slide with your finger or a pencil. Record how the hydra
reacts to this.
4. Observe the hydra under the lowest power of the microscope. Make a microscope
drawing of the hydra. Make a large microscope drawing of the hydra. Look at a textbook
to label as many features of the hydra as you can find. Look for its tentacles, mouth,
base, and bud. Also note whether its mouth and tentacles face upward or downward.
5. Look at the tentacles under medium power. Do NOT use the high power objective. The
small, round cells that can be seen on the tentacles are stinging cells. The stinging cells
inject poison or release a long thread when touched, but the threads are too small to be
seen. Draw stinging cells on your diagram and label them.
6. One person in the group should watch through the microscope while the other person
gently uses a straightened paper clip to touch the tentacles of the hydra. Record the
reactions of the hydra.
7. Use a dropper (cut so the opening is wider) to add a few daphnia to the well slide
containing the hydra. Record your observations of what happens.
8. When you are finished, put the hydra back into its culture. Wash and dry the depression
slide and return it to its box.
Data: observations without microscope, microscope drawing, observations with microscope.
Analysis: (Write answers so you can easily tell what the question was).
1. Why is it challenging to focus on the hydra with the microscope?
2. What are 2 reasons you should NOT use the high power objective for observing the
hydra?
3. Does the hydra seem to react favorably or unfavorably to tapping the slide and to
touch with the paper clip?
4. Which body part of the hydra seemed most sensitive to touch?
5. How does a hydra feed?
6. How do the body parts and reactions of the hydra help it to survive?