How Scientists Work How Scientists Work How do scientists test hypotheses? How does a scientific...

How Scientists How Scientists WorkWork

How do scientists test How do scientists test hypotheses? hypotheses?

How does a scientific How does a scientific theory develop?theory develop?

InquiryInquiry Inquiry Inquiry is the search for information is the search for information

and explanationand explanation Scientists begin an inquiry Scientists begin an inquiry

investigation with a questioninvestigation with a question There are two main types of scientific There are two main types of scientific

inquiry: discovery science and inquiry: discovery science and hypothesis-based sciencehypothesis-based science

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Discovery ScienceDiscovery Science Discovery science Discovery science describes natural describes natural

structures and processesstructures and processes This approach is based on observation This approach is based on observation

and the analysis of dataand the analysis of data


Types of DataTypes of Data Data Data are recorded observations or are recorded observations or

items of informationitems of information Data fall into two categoriesData fall into two categories

QualitativeQualitative, or descriptions rather than , or descriptions rather than measurementsmeasurements

QuantitativeQuantitative, or recorded , or recorded measurements, which are sometimes measurements, which are sometimes organized into tables and graphsorganized into tables and graphs


Fig. 1-23

Induction in Discovery Induction in Discovery ScienceScience

Inductive reasoning Inductive reasoning draws draws conclusions through the logical conclusions through the logical process of inductionprocess of induction

Repeat specific observations can lead Repeat specific observations can lead to important generalizationsto important generalizations For example, For example, ““the sun always rises in the the sun always rises in the

easteast””


Deduction: The Deduction: The ““If…ThenIf…Then”” Logic of Logic of Hypothesis Based ScienceHypothesis Based Science

Deductive reasoning Deductive reasoning uses general uses general premises to make specific predictionspremises to make specific predictions

For example, For example, ifif organisms are made of organisms are made of cells (premise 1), and humans are cells (premise 1), and humans are organisms (premise 2), organisms (premise 2), then then humans humans are composed of cells (deductive are composed of cells (deductive prediction)prediction)


A Closer Look at Hypotheses in A Closer Look at Hypotheses in Scientific InquiryScientific Inquiry

A hypothesis must be A hypothesis must be testable testable and and falsifiablefalsifiable

Hypothesis-based science often makes Hypothesis-based science often makes use of two or more alternative use of two or more alternative hypotheseshypotheses

Failure to falsify a hypothesis does not Failure to falsify a hypothesis does not prove prove that hypothesisthat hypothesis For example, you replace your flashlight For example, you replace your flashlight

bulb, and it now works; this supports the bulb, and it now works; this supports the hypothesis that your bulb was burnt out, hypothesis that your bulb was burnt out, but does not prove it (perhaps the first but does not prove it (perhaps the first bulb was inserted incorrectly)bulb was inserted incorrectly)Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Myth of the Scientific The Myth of the Scientific MethodMethod

The The scientific method scientific method is an idealized is an idealized process of inquiryprocess of inquiry

Hypothesis-based science is based on Hypothesis-based science is based on the the ““textbooktextbook”” scientific method but scientific method but rarely follows all the ordered stepsrarely follows all the ordered steps

Discovery science has made important Discovery science has made important contributions with very little contributions with very little dependence on the so-called scientific dependence on the so-called scientific methodmethod


Scientific MethodScientific MethodStating the ProblemStating the Problem

How do new living things, or How do new living things, or organisms, come into being? organisms, come into being?

Forming a HypothesisForming a Hypothesis Francesco Redi questioned the Francesco Redi questioned the theory of spontaneous theory of spontaneous generationgeneration

flies produce maggotsflies produce maggots

Scientific MethodScientific MethodSetting Up a Controlled Setting Up a Controlled ExperimentExperiment

Recording and Analyzing Recording and Analyzing ResultsResults

Drawing a ConclusionDrawing a Conclusion Publishing and Repeating Publishing and Repeating InvestigationsInvestigations

Setting Up a Controlled Setting Up a Controlled ExperimentExperiment

VariablesVariables - factors in an - factors in an experiment that can change experiment that can change equipment used, type of material, equipment used, type of material, amount of material, temperature, amount of material, temperature, light, and timelight, and time

Only one variable tested at a Only one variable tested at a timetime

All other variables are kept All other variables are kept unchanged, or unchanged, or controlledcontrolled. . controlled experimentcontrolled experiment. .

Types of variablesTypes of variables Independent variableIndependent variable

Manipulated variableManipulated variableWhat you changeWhat you change

Dependent variableDependent variableResponding variable Responding variable Changes in response to Changes in response to manipulated variablemanipulated variable

What you measureWhat you measure

Publishing and Publishing and Repeating InvestigationsRepeating Investigations Needham’s Test of Redi’s Needham’s Test of Redi’s

FindingsFindings mid-1700s, John Needham, mid-1700s, John Needham, an English scientist an English scientist

attacked Redi’s work attacked Redi’s work claimed spontaneous claimed spontaneous generation could occur generation could occur under right conditions under right conditions

heated gravyheated gravy

Publishing and Publishing and Repeating InvestigationsRepeating Investigations

Spallanzani’s Test Spallanzani’s Test of Redi’s Findingsof Redi’s Findings Lazzaro Spallanzani, Lazzaro Spallanzani, ItalianItalian

Broth had not been Broth had not been boiled long enoughboiled long enough

Boiled a container of Boiled a container of broth in a water bath broth in a water bath for 45 minutesfor 45 minutes

Image from: http://www.chemheritage.org/EducationalServices/pharm/antibiot/readings/spogen.htm

Publishing and Publishing and Repeating InvestigationsRepeating InvestigationsPasteur’s Test of Pasteur’s Test of Spontaneous Spontaneous GenerationGeneration In 1864, French In 1864, French scientist, Louis Pasteur scientist, Louis Pasteur

designed a flask with designed a flask with long curved neck long curved neck

showed all living things showed all living things come from other living come from other living things things Image from: http://www.chemheritage.org/EducationalServices/pharm/antibiot/readings/spogen.htm

VerifiableVerifiable What does this word mean?What does this word mean? How does it relate to science??How does it relate to science??

How a Theory How a Theory DevelopsDevelops

Hypothesis may become so well Hypothesis may become so well supported scientists consider it supported scientists consider it a a theorytheory. .

Theories enable scientists to make Theories enable scientists to make accurate predictions about new accurate predictions about new situationssituations

As new evidence is uncovered, a As new evidence is uncovered, a theory may be revised or replaced theory may be revised or replaced by a more useful explanationby a more useful explanation

Precision and AccuracyPrecision and Accuracy PrecisionPrecision

Describes the unit you used to measureDescribes the unit you used to measure The smaller the unit of measurement, The smaller the unit of measurement,

the more precise the measurementthe more precise the measurement AccuracyAccuracy

How close the measurement is to the How close the measurement is to the actual valueactual value

How different your number is from the How different your number is from the accepted valueaccepted value

Qualitative vs. Qualitative vs. quantitativequantitative

QualitativeQualitative Descriptive dataDescriptive data

QuantitativeQuantitative Measurement dataMeasurement data

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