Scientific MethodScientific Method

Steps in the Scientific Steps in the Scientific MethodMethod

ObservationObservation HypothesisHypothesis ExperimentExperiment Data CollectionData Collection ConclusionConclusion RetestRetest

ObservationsObservations

Gathered through Gathered through your your sensessenses

A scientist notices A scientist notices something in their something in their

natural worldnatural world

ObservationsObservations

An An exampleexample of an of an observationobservation might might be noticing that be noticing that

many many salamanders near salamanders near

a pond have a pond have curved, not curved, not

straight, tailsstraight, tails

HypothesisHypothesis

A suggested solution A suggested solution to the problem.to the problem.

Must be Must be testabletestable

Sometimes written as Sometimes written as If…Then…If…Then… statements statements

PredictsPredicts an outcome an outcome

HypothesisHypothesis

An An example of a example of a hypothesishypothesis might might be that the be that the salamanders have salamanders have curved tails due to curved tails due to a pollutant in the a pollutant in the moist soil where moist soil where they live. they live.

ExperimentExperiment

A procedure A procedure to to testtest the the hypothesis.hypothesis.

ExperimentExperiment

VariableVariable – –

factor in the factor in the experiment experiment that is being that is being

testedtested

ExperimentExperiment

A good or A good or “valid” “valid”

experiment experiment will only have will only have ONE variable!ONE variable!

Controls and VariablesControls and Variables

Scientific Experiments Follow Scientific Experiments Follow RulesRules

An experimenter changes one factor and observes or measures what happens.

The Control VariableThe Control Variable

The experimenter makes a The experimenter makes a special effort to keep special effort to keep other other factors constant,factors constant, so that so that they will not effect the they will not effect the outcome.outcome.

Those factors are called Those factors are called control variables.control variables.

What is the Purpose of What is the Purpose of a Control?a Control?

Controls are NOT being tested

Controls are used for COMPARISON

Other Variables

The factor that is changed is known as the independent variable.

The factor that is measured or

observed is called the dependent variable.

Example of Controls & Example of Controls & VariablesVariables

For example: suppose you want to determine the fastest route to walk home from school.

You will try several different routes and time how long it takes you to get home by each route.

Since you are only interested in finding a route that is fastest for you, you will do the walking yourself.

What are the Variables What are the Variables in Your Experiment?in Your Experiment?

Varying the route is the Varying the route is the independent variable.independent variable.

The time it takes for the route The time it takes for the route is the is the dependent variable. dependent variable.

Keeping the same walker Keeping the same walker throughout makes the walker throughout makes the walker a a control variable.control variable.

One more thing… it is best to make several trials with each independent variable.

Valid ExperimentsValid Experiments

Remember: To be a Remember: To be a Valid Experiment:Valid Experiment:

Two groups are required --- the control & experimental groups

There should be only one variable

DataData

Results of the experiment

May be: Quantitative (numbers)

or Qualitative

(descriptive)

DataData

Must be organized

Can be organized into charts, tables, or graphs

ConclusionConclusion

The answer to the hypothesis based on the data obtained from the experiment

RetestRetest

In order to verify the results,

experiments must be retested.

Solving a ProblemSolving a Problem

1) Identify a Problem2) State Observations about

the problem3) Form a Hypothesis about

the problem (if…then…)4) Design an Experiment to

test the hypothesis5) Collect Data6) Form a Conclusion7) Retest

ReviewReview

ALLOMETRIC GROWTH (from the Greek allo meaning "different" and metr meaning “measure”)

Different cell lines/body parts can grow at different rates (relative to an isometrically growing form) during development from juvenile to adult in various species.

Are humans a good example of a species that undergoes allometric growth or are we more isometric?

Do the head, limbs, and body grow at different rates, resulting in a human adult with proportions completely different from those of the newborn baby?

Compare the ratios of two body parts in newborns (data provided in Table 1.1, page 10) and students.

Describe how you will measure each selected body part for each team member. See Table 1.1 for suggested methods.

Include data collection and analysis. We will measure in inches (in)? Need to be consistent with our measurements, so we can

compare data.

The Experiment

Choose two body parts and measure the selected body parts for each team member. We will all use height.

Determine the height of each team member and their head circumference (Tables 1-3).

Divide the height of the individual by the head circumference. This determines the height to body part ratio (H/BP).

Analyze data in a table (collectively) and graph to create Figure 1.

Data Collection Example

Data Collection Example

Table 1.

Height to Ratio for Students and Newborns

Subject Height (in) Head circumference (in) H/BP Ratio

Team member 1

Team member 2

Team member 3

Team member 4

Newborns      

1. Record results for each team member in Table 1.2a.2. Calculate the H/BP ratios for each.3. Record data for newborns from Table 1.1 (page 10).4. Follow the same procedure for the second H/BP

chosen and record the data.5. Each student will enter their H/BP ratios results on

the overhead transparency6. Copy the combined results for the class for the two

comparisons of H/BP ratios on Table 1.3 (provided).

Results

1. Last component of a scientific investigation is to interpret the results and discuss their implications in light of the hypothesis and any supporting literature.

2. Study the results (tables and graphs) and determine if the hypothesis was supported or falsified.

3. If falsified, suggest alternative hypotheses for testing.4. If hypothesis is supported by the data, then suggest

additional experiments to extend the work.5. Critique your experiment. What weaknesses did you

see in the experiment(s)? Suggest improvements.

Discussion(Interpreting and communicating results)

1. Write (typewritten) abbreviated lab report containing:1. Title page2. Results [table(s) and/or graph(s)]Careful with grammar and spelling. See documents posted on Bb as well as Appendix A of the lab manual

“Scientific Writing and Communication” (pages 767-779) for formatting lab report.

2. Answer questions 1a - 1i (Questions for Review Your Knowledge section) on page 19 of the lab manual (on a separate sheet of paper). Turn in separately from the lab report.

Take Home Assignment(Both due at the beginning of next weeks

lab)