Scientific Method in Biology

Observations

Observations are a critical component of science, because they can lead to scientific questions. • Example: Alexander Fleming’s observations

on a bacterial culture contaminated with mold.

Four students were having a discussion about how scientists do their work. This is what they said: Antoine: “I think scientists just try out different things until something works.” Tamara: “I think there is a definite set of steps all scientists follow called the scientific method.” Marcos: “I think scientists use different methods depending on their question.” Avery: “I think scientists use different methods but they all involve doing experiments.” Which student do you most agree with? Explain why you agree with that student and include why you disagree with the other students. (NSTA, 2008)

Discuss with your table partner:

Field Studies Modeling

Scientific Method: Testable Questions o Identifies factor to be tested o Indicates the outcome to be measured/assessed

Discuss with your table partner:

Are the following questions testable? Why or why not? 1. What affects the growth of mold on food? 2. Does phosphate affect the growth of tulips? 3. Does caffeine affect the behavior of fish?

___________________________________________________________________.

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Hypotheses

A hypothesis is a proposed solution for an observable phenomena (or an “educated guess”).

A hypothesis should include a specific and testable prediction (that includes the factor to be tested and the outcome to be measured) and a rationale.

An “If …then…because” format can help you

determine if your hypothesis is complete.

Variables Independent (or Manipulated) Variable:

The factor being tested in an experiment. It should be the ___________________ between

the experimental group and the control group.

Discuss with your table partner

Why is it so critical that an experiment only has one independent (manipulated) variable? What could result if an experiment was set up incorrectly with more than one independent (manipulated) variable?

If there is more than one difference, you would not be able to determine what factor caused the results in the experiment.

An incorrect conclusion may be drawn if there are any other differences between the groups in the experiment other than the factor that was to be tested.

Discuss with your table partner The photos below shows an experiment to test how the color of light affects plant growth. Are there any other differences besides light color that could be affecting the results? If so, how could the experiment be improved?

Dependent (or Responding) Variable: The outcome being assessed in an experiment.

Quantitative Data: Data that can be measured. Examples: __________________________ Qualitative Data: Data which can be observed but not measured. Examples: __________________________

Controlled Variables (or Constants): The many factors that should be ______________

between the control group and the experimental group.

Multiple Samples or

Repeated Trials

An experiment should have multiple samples or repeated trials in order to ensure that the results of the experiment are valid and the results are not due to random fluctuations.

Confirmation Bias Confirmation bias is the natural human tendency to notice information that __________________________, and to ignore information that does not match our expectations. A good scientist must always be aware of the problem of confirmation bias and must attempt to design experiments to avoid this problem.

Double Blind Studies A double blind study is an experiment in which neither the research subject nor the ____________ knows whether the subject is in the experimental group or the control group. (The information is encoded.) This experimental design aims to reduce potential sources of bias (placebo effect, confirmation bias).

At least 12 double blind randomized controlled trials have examined how children react to diets containing different levels of sugar. None of these studies, not even studies looking specifically at children with attention-deficit/hyperactivity disorder, could detect any differences in behavior between the children who had sugar and those who did not. Continued

Avoiding Bias: Double-Blind Experiments

Scientists have even studied how parents react to their kids on sugar. When parents are told their child has been given a drink containing sugar, but it is actually sugar-free, they rate the behavior as more hyperactive than those not given the drink. In fact, the differences in behavior between the two groups were all in the parents’ minds.

Avoiding Bias: Double-Blind Experiments Continued

Scientific Theory

In science, the word theory has a very different meaning than in everyday conversation.

A scientific theory is a

general explanation for a broad range of data. A scientific theory is ____________________.

Infer: To draw a conclusion from facts or premises.

What are observations can you make of the scene on the right?

What are inferences you can make from the scene?

Inferences in Science