Students Methods – Experimental Design/Protocol
Summer Research Program for Science Teachers
South Shore High School, Brooklyn
2000
Can Two Species of Slime Molds Survive Within a Given Physical Space?
[9-12 Content Standard C- Organization in living systems]
Background Information: In nature, slime molds live in soil. There are various species of slime molds. Some slime molds can be distinguished by the color of their fruiting bodies.
Problem: Can two species of slime molds survive within a given physical space?
Teacher Instructions: Begin with the same number of cells. A hemocytometer should be used to determine the number of cells in each Dictyostelium suspension. [9-12 Content Standard E- Understandings about science and technology] Dilute suspension so that 10 ul of Dictyostelium suspension contains 20 cells.
Literature Search:
[9-12 Content Standard A- Abilities necessary to do scientific inquiry]
1. What is the primary source of nutrition for slime molds?
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2. What are the ideal conditions for slime mold survival?
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Formulate your hypothesis: _____________________________________________________
Materials:
1 ml of SM/2 medium inoculated with Inoculating loop metric ruler
1 species of soil bacteria. Bunsen Burner tape
3 2LP agar plates 4 micropipettes dissecting microscope
Dictyostelium discoideum NC4 (yellow wild-type) in suspension
Dictyostelium rosarium (purple) in suspension goggles & gloves
Students Methods – Experimental Design/Protocol
“X” each line upon completion of each step within the protocol
Day 1: Use Gloves and Goggles
[Teaching Standard D- Structure time for extended investigations]
Preparation of Bacterial Streaks-
_____ 1. Turn on, flame and adjust Bunsen burner
_____ 2. Flame inoculating loop until sterile.
_____ 3.Wait until loop is cool, then dip loop in bacterial suspension
_____ 4.“Paint” a horizontal and vertical line crossing at the center of the Petri dish of 2LP agar
_____ 5. Repeat steps 1 – 4 for the remaining Petri dishes
_____ 6. Incubate for two days at 37 C
Day 2: Use Gloves and Goggles
_____ 1. Label one petri dish “EXPERIMENT”, the second “CONTROL A”, the third “CONTROL B”.
_____ 1. Deposit 10 ul of species A Dictyostelium at the center of Petri dish labeled “EXPERIMENT” ( Note: To reduce contamination, never re-use disposable micropipettes.)
_____ 2. Deposit 10 ul of species B Dictyostelium at the center of Petri dish labeled “EXPERIMENT”
_____ 3. Deposit 10 ul of species A Dictyostelium at the center of Petri dish labeled “CONTROL A”.
_____ 4. . Deposit 10 ul of species B Dictyostelium at the center of Petri dish labeled “CONTROL B”.
Seal
all petri dishes with tape
Days 3 -5: Use Gloves and Goggles
Determine the rate of feeding by measuring the movement of the feeding front using a metric ruler( NYCS S6c). Measurements should be taken for 5 days. Observations should be made using a dissection microscope (10x). [9-12 Content Standard E- Understandings about science and technology]
Results
Data Table
Date
Day Average
feeding distance (mm) Average
feeding distance per day
Miscellaneous
(= distance line a + distance line b /2 ) (= average distance day z – average distance y )
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Results
Represent your results using diagrams, charts and/or graphs in an effective manner; such that, it can be explained clearly to a person who did not perform this scientific investigation.
Conclusion
Was your hypothesis correct? Explain
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Follow-up questions:
Is there evidence of competition between the species of slime molds within the Petri dishes? Describe and explain how there is or is not evidence of competition. [9-12 Content Standard A- Formulate explanations using evidence]
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Is there evidence of cooperation between the species of slime molds within the Petri dishes? Describe and explain how there is or is not evidence of cooperation.
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How does the behavior of the slime molds in the Petri dishes relate to organisms in aquatic or terrestrial ecosystems? [9-12 Content Standard C- Interdependence of organisms] _________________________________________________________________________
Propose another way to determine if 2
species of slime molds can co-exist in the same space.
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