Lab: Nervous Systems and BehaviorName ______

Period _____ Date ______

Introduction.

In this lab you will be studying the structural differences among three different organisms and relate these differences to how each organism is able to respond to various stimuli.

Paramecium Hydra Planaria

  • The paramecium is a single cell organism with no nerve cells or nervous system.
  • The hydra has a network of nerve cells extending through the entire animal (called a nerve net) but no specialized group of nerve cells (central nervous system, including a brain).
  • Planaria have central nervous system and a simple brain, two nerve cords running down the body and many sensory cells.

Animals exhibit two basic kinds of behavior: inherited and learned. Animals with complex nervous systems can learn new behaviors and adjust their inherited behaviors to new situations. In animals without complex nervous systems, almost all behavior is inherited.

Questions:

  1. Which of the organisms described above would you predict is most reliant on innate (inherited) behaviors?
  1. Which of the organisms described above would you predict is most able to learn and adjust its behaviors?

Inherited behaviors exhibit predictable responses to stimuli. In this lab you will observe the way these organisms move (taxis; plural taxes) in response to stimuli. A movement toward a stimulus is a positive taxis; a movement away from a stimulus is a negative taxis.

The taxes we will be concerned with in this lab are:

  • phototaxis (movment in response to light)
  • thigmotaxis (movement in response to touch)
  • chemotaxis (movement in response to chemicals)
  • thermotaxis (movement in response to heat)

Purpose

  • To related the nervous system complexity of organisms to their behavior in response to various stimuli.
  • To analyze the adaptive value of the organisms’ responses.

Procedure

Design your own experiments using the information below for guidance.

Paramecium

Materials needed: light microscope, slides, cover slips, cotton, acetic acid.

Behaviors to test:

Thigmotaxis. Use a pipette to place a paramecium on a slide with a few cotton fibers. Use a microscope to observe what happens when the paramecium comes in contact with the thread. Draw and include written explanations of what you see.

Phototaxis. Use the lowest power objective lens. Shift the diaphragm so that half the field of view is covered. Wait 2 minutes. Shift the diaphragm back into place and count the number of paramecium on the light side and the side that was dark. Make a bar graph of the number of paramecium on the light vs. the dark side.

Chemotaxis. Introduce a few fibers of cotton that have been dipped in acetic acid. Draw and include written explanations of what you see.

Hydra

Materials needed: watch glass, dissecting scope, probe, acetic acid.

Behaviors to test:

Thigmotaxis. Use a pipette to place a hydra on a watch glass and touch it with a probe while watching through a dissecting scope. Draw and explain what you see. Does the whole hydra react or just the area stimulated?

Phototaxis. Observe the hydra in low light and then with more light. Draw and explain behaviors observed.

Chemotaxis. Introduce a little cotton dipped in acetic acid. Draw and explain hydra reactions.

Thermotaxis. Light a match and stick the tip of a probe in the flame. Put the probe in the water NEXT TO (not toughing) the hydra. Draw and explain the responses observed.

Planaria

Materials needed: dissecting scope, watch glass, probe, acetic acid, black paper.

Behaviors to test:

Thigmotaxis. Use a pipette to place a planaria in a watch glass with some water from the culture. Touch the planaira with a probe in different places and with varying amounts of pressure. Draw and explain what you observe. Does it matter if you touch the anterior (front) or posterior (back) of the planaria? Does the response change when you touch harder or softer?

Chemotaxis.Introduce a little cotton dipped in acetic acid to the watch glass. Draw and explain planaria reactions.

Thermotaxis. Light a match and stick the tip of a probe in the flame. Put the probe in the water NEXT TO (not touching) the planaria. Draw and explain the responses observed.

Phototaxis. Observe the planaria stock culture container. Half of the dish is covered and half is exposed to light. Count the number of planaria in the dark and the number exposed to light. Make a bar graph.

Conclusion

  1. Relate the structural characteristics to the behaviors observed for each organism.
  1. Discuss the type of behavior observed for ONE organism (eg: positive phototaxis) and the adaptive value of the behavior (how does it enhance the organism’s survival).