Experiment TermsExperiment Terms

Theory vs. HypothesisTheory vs. Hypothesis

A A hypothesis hypothesis is a proposed is a proposed testabletestable explanation for an observable phenomenon. explanation for an observable phenomenon.

When a set of hypothesis is When a set of hypothesis is

confirmed to be true many confirmed to be true many

times, it is then reclassified times, it is then reclassified

as a as a theorytheory!!

Some Example TheoriesSome Example Theories Basic theories of biology are:Basic theories of biology are:

Cell theoryCell theory: all organisms are made of cells.: all organisms are made of cells.Biogenesis theoryBiogenesis theory: life only comes from life.: life only comes from life.Evolution theoryEvolution theory: living things have a common : living things have a common ancestor and are adapted.ancestor and are adapted.Gene theoryGene theory: Organisms contain coded : Organisms contain coded information that determines their form, function, information that determines their form, function, and behavior.and behavior.

Other Theories:Other Theories: Germ TheoryGerm Theory - proposes that microorganisms - proposes that microorganisms are the causes of many diseasesare the causes of many diseasesHeliocentric TheoryHeliocentric Theory - the sun is the center of the - the sun is the center of the solar system, planets revolve around the sunsolar system, planets revolve around the sunLaw of GravityLaw of Gravity - masses attract each other - masses attract each other

Practice QuestionPractice Question

Which is NOT a valid hypothesis?Which is NOT a valid hypothesis?

A. Bluebirds sing to attract mates. A. Bluebirds sing to attract mates.

B. Bluebird songs are beautiful.B. Bluebird songs are beautiful.

C. Only male bluebirds sing. C. Only male bluebirds sing.

D. Sparrows will leave territories where they D. Sparrows will leave territories where they hear bluebird songs hear bluebird songs

Control group vs. experimental Control group vs. experimental group group

Control groupControl group – provides a normal – provides a normal standard to which the experimental group standard to which the experimental group can be compared. It is CONSTANT! can be compared. It is CONSTANT!

Experimental groupExperimental group – experimental group – experimental group consists of what is being MANIPULATED!consists of what is being MANIPULATED!

Practice QuestionPractice Question The purpose of including a control in a The purpose of including a control in a scientific investigation is to provide what? scientific investigation is to provide what?

a. A basis for comparison.a. A basis for comparison.

b. A correction for experimental errors. b. A correction for experimental errors.

c. A preliminary trial of the methods. c. A preliminary trial of the methods.

d. An opportunity for repetition of the d. An opportunity for repetition of the experiment.experiment.

  

Independent vs. Dependent Independent vs. Dependent VariableVariable

Used in an experiment to keep track of Used in an experiment to keep track of what's going on. what's going on.

Used to measureUsed to measure your results and draw your results and draw accurate conclusions. accurate conclusions.

Are relatedAre related to one another. to one another.

Independent vs. Dependent Independent vs. Dependent VariableVariable

Independent variableIndependent variable – what – what you changeyou change in order to do your experiment. in order to do your experiment.

There should be There should be only oneonly one independent independent variable for any valid experiment.variable for any valid experiment.

Independent vs. Dependent Independent vs. Dependent VariableVariable

Dependent variableDependent variable - what changes when - what changes when the independent variable changes the independent variable changes the dependent variable the dependent variable depends depends onon the the

outcome of the independent variable. outcome of the independent variable.

There can be more than one dependent There can be more than one dependent variable. variable.

Independent vs. Dependent Independent vs. Dependent VariableVariable

Example experimentExample experiment: : You want to measure You want to measure and compare the and compare the growth rate of plants…growth rate of plants…

under full sunlight for under full sunlight for 8 hours a day8 hours a dayversusversus plants that only have plants that only have 4 hours of full sunlight 4 hours of full sunlight

per day. per day.

Independent vs. Dependent Independent vs. Dependent VariableVariable

Independent variableIndependent variable – the amount of time – the amount of time per day of full sunlight (you control this!)per day of full sunlight (you control this!)

Dependent variableDependent variable - the growth rate of - the growth rate of the plants. the plants.

Controlled Variable Controlled Variable

A A Controlled VariableControlled Variable is anything else that is anything else that could influence the dependent variables. could influence the dependent variables. must be carefully monitored and kept must be carefully monitored and kept equalequal in in

your experiments.your experiments. ExampleExample:: Could the amount of water Could the amount of water

affect the growth of our plants? affect the growth of our plants? Yes, so you need to make sure that each Yes, so you need to make sure that each

plant gets the same amount of water in the plant gets the same amount of water in the experiment. experiment.

In this way you eliminate water as a possible In this way you eliminate water as a possible source of difference between your plants. source of difference between your plants.

Practice QuestionsPractice Questions A researcher investigated two groups of A researcher investigated two groups of

fruit flies. fruit flies. Population A was kept in a 0.5 L container.Population A was kept in a 0.5 L container.

Population B was kept in a l.0 L container.Population B was kept in a l.0 L container.

Below is a graph showing the growth of Below is a graph showing the growth of these two populations.these two populations.

What is the manipulated (independent) variable?What is the manipulated (independent) variable?

A. The number of flies.A. The number of flies.

B. The time in days.B. The time in days.

C. The numbers of groups studied.C. The numbers of groups studied.

D. The size of the containers.D. The size of the containers.

A researcher investigated two groups of fruit flies.A researcher investigated two groups of fruit flies. Population A was kept in a 0.5 L container.Population A was kept in a 0.5 L container.Population B was kept in a l.0 L container.Population B was kept in a l.0 L container.

What is the dependent variable?What is the dependent variable?A. The number of flies.A. The number of flies.B. The time in days.B. The time in days.C. The numbers of groups studied.C. The numbers of groups studied.D. The size of the containers.D. The size of the containers.

A researcher investigated two groups of fruit flies.A researcher investigated two groups of fruit flies. Population A was kept in a 0.5 L container.Population A was kept in a 0.5 L container.Population B was kept in a l.0 L container.Population B was kept in a l.0 L container.

Which of the following is a logical inference Which of the following is a logical inference based on the contents of the graph?based on the contents of the graph?

A.A. The flies in Group B were healthier than those The flies in Group B were healthier than those in Group A.in Group A.

B. A fly population with more available space will B. A fly population with more available space will grow larger than a population with less space.grow larger than a population with less space.

C. If Group B were observed for 40 more days, the C. If Group B were observed for 40 more days, the size of the population would double.size of the population would double.

D. In 40 days, the sizes of both populations would D. In 40 days, the sizes of both populations would decrease at the same rate.decrease at the same rate.

Practice QuestionsPractice Questions

Which variable is measured rather Which variable is measured rather

than manipulated? than manipulated?

A.A. Independent variableIndependent variable

B.B. Dependent variable Dependent variable

Practice QuestionsPractice Questions

Positive people have more friends Positive people have more friends

than negative people. Which than negative people. Which

statement is correct?statement is correct?

A.A. The dependent variable is the positivity of the The dependent variable is the positivity of the person person

B.B. The dependent variable is the number of The dependent variable is the number of friends friends

Practice QuestionsPractice Questions

Smoking causes lung cancer. Smoking causes lung cancer.

Which statement is correct? Which statement is correct?

A.A. The independent variable is lung cancer The independent variable is lung cancer

B.B. The independent variable is smoking The independent variable is smoking