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# Experimental Design and the Bacteria lab

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### Experimental Design and the Bacteria lab

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