Carmen M. Simon                                                                                                                            Return to Biology Menu

South Shore High School, Brooklyn

Summer 2001




              All living things strive to survive. Dictyostelium are soil dwelling amoeba that feed on bacteria. Most organisms, including Dictyostelium, thrive at optimal conditions which include temperature, moisture, food availability, pH, and light intensity. Dictyostelium prefers relatively dark, warm (20' C), slightly acidic and moist environments.   When food is plentiful, Dictyostelium cells live independently of each other as singled celled amoebae.  However, when food is scarce, Dictyostelium  cells aggregate (combine) to form multicellular stationary mounds which eventually develop into slithering slugs.  When slugs find an appropriate environment for continued development, they form fruiting bodies.  The fruiting bodies consists of 2 structures, the stalk and the sorus (head) that contain spores.  Fruiting bodies burst to disperse spores so that they may be carried by the wind or animals to an environment more suitable for survival.  When spores land in a food-rich, moist environment, they will geminate.  Dictyostelium will, once again, live as unicellular independent amoebae; until the next crisis. During this investigation, we will observe the behavior of Dictyostelium discoideum when exposed to white light in an environment that has a limited food supply.


Problem:  How will starving Dictyostelium discoideum slugs respond to white light?

Hypothesis: Starving Dictyostelium discoideum slugs will be attracted to/repelled by

white light?                                                                                                                                          choose 1




            per class

1 Petri dish containing developing Dictyostelium discoideum

1 roll of adhesive tape


            per group of 3 to 4 students

3 Petri dishes containing non-nutrient agar (NNA)                    

1 Sharpie marker

1 disposable micropipette

1  microfuge tube containing 100ml bacterial culture

2 strips of aluminum foil  25 cm (10 inches)

1 toothpick


Experimental Design:

1. Using the Sharpie marker, draw a square (1cm2) at the center of the outside of the bottom portion of your 3 Petri dishes. Label the poles of the dishes; north, south, east, and west.

2. Squeeze the micropipette bulb to expel the air.  Submerge the tip into the microfuge tube containing the bacterial culture.  Release the bulb to take in 25ml of bacterial culture.

3. Open the Petri dish by removing the top portion.

4. Squeeze the 25ml of bacterial culture onto the non-nutrient agar at the center of the Petri dish.  Immediately close the Petri dish to reduce contamination of the specimen (as well as to yourself).


5.  Allow bacterial culture to  dry on Petri dishes for approximately 10 minutes.

6. Using the wide tip of the tooth pick, swipe a small sample of the Dictyostelium culture.

7. Gently poke the center of the Petri dish with your sample.  Repeat steps 6 & 7 for each Petri dish.

8.   a) Petri dish #1- Tape shut. Incubate at room temperature in the light.

      b) Petri dish #2- Tape shut. Incubate at room temperature in the dark. That is, wrap Petri dish completely with foil.  Be certain that no light can enter the dish.

      c) Petri dish #3- Tape shut.  Wrap dish completely with foil.  Make a small hole, about the size of the head of a pin, on the NORTH  side of the dish. Note: The cells should perceive the light from the side, not from above.  Incubate at room temperature in the light.

9.  Observe in 48 hours for slug development.

10. Measure the distance of slug movement from the center of the dish and determine the slug orientation by observing the slug tip direction. Collect data for at least 5 slugs per direction per plate.  Average the distance traveled for each direction. Graph your results. 


Data Tables

Petri Dish # 1                     (5 measurements each)

          Direction                     Distance Traveled (mm)        Average in mm






 Petri Dish # 2                  (5 measurements each)

          Direction                     Distance Traveled (mm)                    Average in mm






Petri Dish # 3                  (5 measurements each)

          Direction                     Distance Traveled (mm)                    Average in mm






Data Analysis-    draw a bar graph.

a. Label the x-axis, "direction traveled".  Label the y-axis, "average distance traveled in mm".

b. Determine and label an appropriate scale for the y-axis.

c. Your graph should contain 3 bars above each direction. One bar for each Petri dish.


Conclusion-  Based on the data you collected, was your hypothesis correct?

Post-lab questions

1. Dictyostelium live in the soil where it is relatively dark.  The Dictyostelium cells in our investigation were placed in an environment that had a limited food supply. 

 Based on the results of this investigation, what inference can be made about the response of starving Dictyostelium  slugs to white light and their need to survive in nature?

2. What was an external stimulus (change) that occurred within the environment that caused the Dictyostelium slugs to respond white light?

3. What was an internal stimulus (change) that occurred within a Dictyostelium  slug that made it respond to the white light?

4. Did Dictyostelium  slugs learn this response to the white light or was it an innate response?

5.How do you think the starving unicellular amoeba communicated with the other starving unicellular amoeba?

6. Think! How did the slugs sense the location of the light?

7. How does the response of  Dictyostelium to white light make it fit to survive?

8. Describe 3 similarities Dictyostelium has with humans.


Correlation to the National Standards:

Content Standards

Topic- The Behavior of Organisms

Description:  Organisms have behavioral responses to internal changes and to external stimuli.  Responses to external stimuli can result from interactions with the organism's own species and others, as well as environmental changes; these responses either can be innate or learned.  The broad patterns of behavior exhibited by animals have evolved to ensure reproductive success.  Animals often live in unpredictable environments, and so their behavior must be flexible enough to deal with uncertainty and change.



Bozzone, D. M. 1987.  A Practical Guide to the Use of Cellular Slime Molds for

            Laboratory Exercises and Experiments.  Department of Biology, Saint Michael's

            College, Colchester, Vermont

Kessin, R.H. and Van Lookeren Campagne , M.E.(1992) The Development of a Social

            Amoeba. American Scientist 80: 556-565.



Materials and kits can be purchased through 

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