Scientific Method

What is it Good For?

• Absolutely something!!• Logical approach to problem

solving• Reliable• Can provide “proof”

Steps in the Scientific Method

• Observation• Hypothesis• Experiment• Collect data• Draw a conclusion• Retest

Observation• Gather information

with your senses• Question what you

observe

Hypothesis

• A prediction, or educated guess

• “I think that…”• Does not have to

be correct!... but has to be able to be tested.

Experiment

• Procedure designed to test your hypothesis

• We will come back to talk about parts of an experiment!

Collect Data

• Results of the experiment

• May be quantitative (numbers) or qualitative

Conclusion

Retest• Why is this necessary?–Helps verify results

• Testing again (especially by different groups) makes conclusions more reliable.

Parts of an Experiment

• Independent and dependent variables• Constants• Control and experimental groups

Example Experiment j

• Observation: My artichokes are not growing as quickly as I want.

• Hypothesis: I think that my artichokes will grow faster if I water them daily.

• Experiment: I will divide my artichoke garden into two groups. Group A will be watered everyday. Group B will not get water. I will measure their growth every week for two months. Each group will have the same type and number of artichoke, the same soil, and the same amount of sunlight.

Independent Variable• The factor that is being changed or tested in an

experiment• Hint: The independent variable is what I can change

or control.• Experiment: I will divide my artichoke garden into

two groups. Group A will be watered everyday. Group B will not get water. I will measure their growth every week for two months. Each group will have the same type and number of artichoke, the same soil, and the same amount of sunlight.

• Can you identify the independent variable?

Dependent Variable• Your results!• The outcome… what is being observed or

measured.• Experiment: I will divide my artichoke garden into

two groups. Group A will be watered everyday. Group B will not get water. I will measure their growth every week for two months. Each group will have the same type and number of artichoke, the same soil, and the same amount of sunlight.

• Can you identify the dependent variable?

Constants• Every factor besides the independent variable

must remain the same so you know for sure what has affected your results.

• Experiment: I will divide my artichoke garden into two groups. Group A will be watered everyday. Group B will not get water. I will measure their growth every week for two months. Each group will have the same type and number of artichoke, the same soil, and the same amount of sunlight.

• Can you identify some constants?

Experimental Group

• The group that is being tested/experimented on.• Experiment: I will divide my artichoke garden into

two groups. Group A will be watered everyday. Group B will not get water. I will measure their growth every week for two months. Each group will have the same type and number of artichoke, the same soil, and the same amount of sunlight.

• Which is the experimental group?

Control Group

• One group of test subjects is used for comparison.• They do not get exposed to the i.v.• Experiment: I will divide my artichoke garden into

two groups. Group A will be watered everyday. Group B will not get water. I will measure their growth every week for two months. Each group will have the same type and number of artichoke, the same soil, and the same amount of sunlight.

• Which group is the control?

“The Slow Death of Spontaneous Generation” Questions

1. Explain and give examples why the theory of spontaneous generation was so believable.

2. Summarize the experiments performed by Redi, Needham, and Spallanzani. Why were none of these able to disprove spontaneous generation?

3. What was the significance of Pasteur’s experiment? Why was it more significant than the previous experiments?

4. Read Pasteur’s experimental procedure and identify the independent and dependent variable and experimental and control groups.

5. Come up with three factors you think should have been kept constant between the experimental and control group.

ReviewTimothy is testing his hypothesis that eating carrots will help his rabbits live longer. He has two rabbits. Rabbit A he feeds one carrot everyday. Rabbit B does not get carrots. Both rabbits are the same age, get the same type of food, and the same exercise. He does this for 3 years until Rabbit B dies. Identify the following factors from his experiment:• Hypothesis • Independent/dependent variables• Experimental/control groups• Constants• Did his results support his hypothesis?

Design an ExperimentHoneybees play an important role in agriculture by pollinating at least 90 different species of food plants. As a result, beekeeping or apiculture, is a multi-million dollar business. However over the last few years, honey bee populations are crashing with hives dying off in less than a week, without an obvious cause. Ian Lipkin a senior researcher at Columbia University believes the cause to be a pathogen (virus, bacteria or fungus) of some sort.• What is the hypothesis?• Help Dr. Lipkin design an experiment to test this hypothesis.• What are your independent and dependent variables?

Experimental and control group? What are 3 factors that should be kept constant?

Design an Experiment

• Question: Will E. coli bacteria population growth decrease as the temperature decreases?

• With your partner:– Make a hypothesis– Design an experiment to test your hypothesis. It

should include (and identify) independent and dependent variables, experimental and control groups, and at least three constants.

DataTemp. (⁰C) # E. coli after 10 Days

0 502 804 856 1108 200

10 27512 35014 48016 65018 89020 1300