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Experimental Design and the Bacteria lab
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Experimental Design and the Bacteria lab

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  • 1. DESIGNING AN EXPERIMENT (Experiment Design) variables constant experimental control dependent independent
  • 2. Variables Independent Dependent Constant Experiment Test Group Control Group
  • 3. FAIR TEST
    • Make sure we are testing the right thing
    • Example: Determine if this is fair or not:
      • In science next week, you take your quiz on:
        • Ancient civilizations
        • Chemical equations
      • What would be fair?
  • 4. Control Group - used to make comparison with experi-mental groups - Allows us to see how the indep. variable changed our results -set up this group exactly the same experimental group EXCEPT don’t give/don’t do the independent variable - “Fair Test”
  • 5. Experimental/ Test Group Setup containing independent variable
  • 6. Variable -used as a Noun in science Root word: vary (verb) = to change Ex) the weather can vary (verb) Ex) the type of weather will be a variable in our experiment (noun)
  • 7. Independent Variable = the variable that is we get to decide/choose what we want to change -should only have 1 independent variable to make it a “fair test” -then use this to START/set up the experiment
  • 8.                                                                     
  • 9. Dependent Variable the result/outcome of the experiment What we measure/observe AFTER completing the experiment
  • 10. Constant Variables Factors that are kept the same throughout the experiment. =Fair test
  • 11. What is the effect of sunlight on the growth of plants?
  • 12. The Effect of Sunlight on the Growth of Plants Control Group Experimental Group Constant Variables Independent Variable Dependent Variable
  • 13. Problem: Where will bacteria grow best? How does the location affect the growth of bacteria? Control Group Constant Variables Independent Variable Dependent Variable
  • 14. Bacteria Lab- Where can Life be Found?
    • Label the petri dish halves #1-4
    • Choose 3 locations and record in notebook
      • #1 = nothing, #2= ?, #3= ?, #4= ?,
    • Leave petri dishes on desk and go get swab of your chosen locations
      • Be sure to roll the swab around to cover all of it’s surface
    • Use S pattern to press swab onto surface of petri dish
      • Be sure to put the correct swab location with the correct petri dish number (as recorded above)
    • Tape the petri dishes shut
    • Put petri dishes in plastic bag and label bag
  • 15. Problem: Where will bacteria grow best? How does the location affect the growth of bacteria? Control Group Constant Variables Independent Variable Dependent Variable
  • 16. Hypothesis
    • Prediction of what results will be
    • “ Educated” guess because based on prior experiences and knowledge
    • If….then…..because…..
      • If I do (explain what you will do in your experiment
      • Then (explain what will happen= your prediction)
      • Because (give a reason why you made your prediction by referring to previous experiences/knowledge
  • 17. BACTERIA OBSERVATIONS Observations (____ days later): ______________________________________________________________________________________________________________________________________________________ Bacteria Culture Location: _______________________ Date: __________________________ Time:___________________________
    • Make notes about:
      • size and number of colonies
      • color and shape of colonies
    • Can you determine how many different types of bacteria there are?
    • Caution: DO NOT OPEN THE
    • ZIP LOC BAGS
  • 18. Control Group Constant Variables Independent Variable Dependent Variable Control Group Constant Variables Independent Variable Dependent Variable