Laboratory Investigation: Observing the Characteristics of Life

Laboratory Investigation: Observing the Characteristics of Life

Purpose: In this lab, students will observe a living organism to identify ways that it exhibits the characteristics of life.

Background: The planaria is a flatworm. This particular species lives in freshwater. They are free-living, are scavengers and feed upon fish, worms, and any other source of protein they can find. When they find food, they climb on top of it, and a muscular tube called a pharynx emerges from their mouth. The pharynx secretes an enzyme that softens their food. Then the pharynx sucks up the softened food, and digestion is completed inside a hollow tube called a gastrovascular cavity (GVC). Waste is excreted through their mouth. They glide along their environments by secreting slime and pushing through it with cilia that line their belly. For their size, they have well-developed nervous systems. They have projections on either side of their heads called auricles that can detect chemical changes in the environment. They have eyespots that detect light, they have nerves that allow them to react to touch, and they even have a small brain and have been taught to go through mazes! There is nothing to support their bodies, like our bones support us, so they are very vulnerable. They have no blood, blood vessels or heart, so nutrients are passed from cell to cell by a process known as diffusion. They breathe through their skin. What is most remarkable about them is their ability to regenerate. When cut in half, each half grows into a new worm. They can also reproduce sexually. They are hermaphrodites, meaning they have both male and female sex organs, so they produce both eggs and sperm. When they reproduce sexually, they have sex, exchange sperm, and each planaria gets pregnant.

Materials: Microscope, prepared slides of planaria, planaria, petri dish, spring water, egg, pipette, probe, penlight, black paper, salt, hand lens, Epsom salt, and scalpel

Hypothesis:

How do you predict the planaria will react to light, touch, and salt?

Procedure:

1. Remove a planarian from the jar at the front of the room using a pipette. Place it in a petri dish with enough water to just cover the bottom.

2. Examine the animal using a hand lens.

A. Describe the dorsal surface.

B. Make a drawing of the dorsal surface and label the parts you are able to see.

C. Describe the way in which it moves.

3. Check the planarian’s reaction to various stimuli.

A. Create a current in the water of the petri dish using a pipette. How does it react?

B. The projections on each side of the head are called auricles. Touch them with the probe. How does the animal react?

C. Touch the other areas of the body and describe its reactions.

D. Place a crystal of table salt in the water (DO NOT PUT THE SALT ON THE ANIMAL!). Describe its reaction. Then, carefully change the water.

4. Carefully hold the planaria above your head to observe the ventral side. Use your hand lens.

A. Describe the ventral surface.

B. Make a drawing of the ventral surface and label the parts.

5.  Using the penlight, shine a beam of light on the anterior region and the eyespots. What is its response?

6. Using your pipette, carefully move the planaria to the center of the petri dish. Place a lid on top that has been partially covered with black paper. Record below under which type of lighting the planaria seems to spend the majority of its time (observe for a few minutes to determine

this).

7. Bring your planaria to the front of the room and obtain a small piece of egg yolk. Place it in the dish and observe the planaria feeding for 10 minutes. Record your observations below. Then, remove the egg yolk from your petri dish.

8.  Add a few crystals of Epsom salts. Wait a few minutes. The planaria will be anesthetized. Decide how you will cut your planaria to allow it to regenerate. See the diagram below for possible cuts. With a razor blade, cut the planaria in the desired location and transfer each half to a separate jar with a little spring water. Make only one cut.

9.  Place your planaria in the tank at the center of the room. They will live there for a period of 2 weeks, during which time we will observe them on occasion to witness their regeneration.

10.  Get a slide of the planaria, and examine it under the microscope. Draw and label any parts you can see.

Analysis

Based on your observations of the planaria, answer the following questions regarding how the planaria fit the characteristics of life.

1.  How did the planaria show the characteristic of organization? What evidence did you see? Did you see any organs?

2.  Is the planaria unicellular or multicellular? How do you know?

3.  What evidence did you see that the planaria requires energy? What did it do/what should it do?

4.  How is the way the planaria requires energy different from what a plant would do? Describe what a plant would do.

5.  The planaria can reproduce two ways, sexually and asexually. Which way is being observed by cutting the worm in half? Explain why you classified this type of reproduction as such.

6.  You saw several ways that the planaria can respond to stimuli. Name the various stimuli.

7.  Name the various responses that could be seen to the above stimuli.

8.  Over the next 2 weeks, both growth and development will be observed in the planaria as they regenerate. What will growth look like? What will development look like?

9.  Name 3 adaptations that the planaria has, and how each of those adaptations helps the planaria to survive in the wild.

10.  Explain why the characteristic of homeostasis could not be observed with the planaria. What might this characteristic look like in a dog?