thinking like a scientist 1.d. think logically and use evidence

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Biology Warm Up: Copy these assignments into your binder. Be sure to include dates and page numbers

August 30-31WarmUp: AgendaLab: Using a Compound Microscope p29Homework: Read and take complete notes 1.1 and 1.2answer q1-5p15 DUE NEXT CLASS

September 1WarmUp: Hypothesis/Procedure/ObservationsQuickLab: What are the Characteristics of Living Things?p18Homework: Read and take notes 1.3 answer q1-6p22

DUE NEXT CLASSSeptember 2-3WarmUp: Levels of OrganizationInClass: Safety Contract and quizInClass: Applying the Scientific Method p31LabManualQuiz: sections 1.1 – 1.3Homework: No homework over Labor Day Weekend!When you finish, please read the procedure for the Compound Microscope lab on page 29. Write a summary for each step of the procedure.

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Thinking Like a Thinking Like a ScientistScientist1.d. Think logically and use 1.d. Think logically and use evidenceevidence

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Aristotle (384 –322 BC)Aristotle (384 –322 BC)Proposed theory of Proposed theory of spontaneous generationspontaneous generationAlso called Also called abiogenesisabiogenesisLiving things can arise from Living things can arise from nonlivingnonliving matter matterIdea lasted almost Idea lasted almost 2000 2000 yearsyears

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Examples of Examples of Spontaneous Spontaneous GenerationGeneration

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Example #1Example #1Observation:Observation: Every year in the Every year in the spring, the spring, the Nile River floodedNile River flooded areas of Egypt along the river, areas of Egypt along the river, leaving behind nutrient-rich leaving behind nutrient-rich mud that enabled the people mud that enabled the people to grow that year’s crop of to grow that year’s crop of food. However, along with the food. However, along with the muddy soil, muddy soil, large numbers of large numbers of frogsfrogs appeared that weren’t appeared that weren’t around in drier timesaround in drier times

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Example #1Example #1Hypothesis:Hypothesis: It was perfectly It was perfectly obvious to people back then obvious to people back then that that muddy soil gave rise to muddy soil gave rise to the frogsthe frogs

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Example #2Example #2Observation:Observation: In many parts of In many parts of Europe, medieval farmers Europe, medieval farmers stored stored grain in barnsgrain in barns with with thatched roofs (like thatched roofs (like Shakespeare’s house). As a roof Shakespeare’s house). As a roof aged, it was not uncommon for aged, it was not uncommon for it to start leaking. This could it to start leaking. This could lead to lead to spoiled or moldy grainspoiled or moldy grain, , and of course there were and of course there were lots of lots of mice aroundmice around..

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Example #2Example #2Hypothesis: It was obvious It was obvious to them that the to them that the mice mice came from the moldy came from the moldy grain.grain.

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Example #3Example #3Observation:Observation: Since there were Since there were no refrigerators, the no refrigerators, the mandatory, daily trip to the mandatory, daily trip to the butcher shop, especially in butcher shop, especially in summer, summer, meant battling the meant battling the flies around the carcassesflies around the carcasses. . Typically, carcasses were “hung Typically, carcasses were “hung by their heels,” and customers by their heels,” and customers selected which chunk the selected which chunk the butcher would carve off for butcher would carve off for them. them.

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Example #3Example #3Hypothesis: Obviously, the Obviously, the rotting meatrotting meat that had been that had been hanging in the sun all day was hanging in the sun all day was the the source of the fliessource of the flies. .

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Abiogenesis RecipesAbiogenesis RecipesRecipe for mice:Recipe for mice: Place a Place a dirty shirtdirty shirt or some rags or some rags

in an in an open pot or barrelopen pot or barrel containing a containing a few grains of few grains of wheatwheat or some wheat bran, and or some wheat bran, and in in 21 days21 days, mice will appear. , mice will appear. There will be adult males and There will be adult males and females present, and they will females present, and they will be capable of mating and be capable of mating and reproducing more mice.reproducing more mice.

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Testing a Testing a Hypothesis:Hypothesis:

The controlled The controlled experiment.experiment.

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Francesco RediFrancesco Redi

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Step 1 - ObservationStep 1 - ObservationThere were flies around There were flies around meat carcasses at the meat carcasses at the Butcher shop.Butcher shop.Where do the flies come Where do the flies come from?from?Does rotting meat turn Does rotting meat turn into or produce rotting into or produce rotting flies?flies?

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Step 2 - HypothesisStep 2 - Hypothesis

Rotten meat does not Rotten meat does not turn into flies. turn into flies. Only flies Only flies can make more flies.can make more flies.

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Redi’s (1626-1697) Experiments

Evidence against spontaneous Evidence against spontaneous generation:generation:

1. 1. Unsealed Unsealed – maggots on meat– maggots on meat2. 2. SealedSealed – no maggots on meat – no maggots on meat3. 3. GauzeGauze – few maggots on gauze, none on – few maggots on gauze, none on

meatmeat

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Redi’s (1626-1697) Experiments

In a controlled experiment, the scientist In a controlled experiment, the scientist changes only one variable, the changes only one variable, the manipulatedmanipulated variable.variable.

What is the manipulated variable in this experiment?

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Redi’s (1626-1697) Experiments

The variable the scientist, observes, The variable the scientist, observes, measures, and records is the measures, and records is the respondingresponding variable.variable.

What is the responding variable in this experiment?

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Redi’s (1626-1697) Experiments

It is called a controlled experiment because all It is called a controlled experiment because all other variables are not allowed to change. other variables are not allowed to change. Those other variables are the Those other variables are the controlledcontrolled variables.variables.

List several controlled variables for this experiment.

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Anton van Leeuwenhoek Anton van Leeuwenhoek (1674)(1674)

Leeuwenhoek began Leeuwenhoek began makingmaking and and looking through looking through simple microscopessimple microscopesHe often made a new microscope for He often made a new microscope for each specimeneach specimenHe He examined waterexamined water and visualized and visualized tiny animals, fungi, algae, and single tiny animals, fungi, algae, and single celled protozoa; celled protozoa; “animalcules”“animalcules”By end of 19By end of 19thth century, these century, these organisms were called organisms were called microbesmicrobes

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Anton van Leeuwenhoek 1632-Anton van Leeuwenhoek 1632-17231723

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Leeuwenhoek’s MicroscopeLeeuwenhoek’s Microscope

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Needham’s ExperimentNeedham’s Experiment

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Lazzaro Spallanzani’s (1765)Lazzaro Spallanzani’s (1765)Boiled soups for almost an Boiled soups for almost an hourhour and sealed containers by and sealed containers by melting the slender necks melting the slender necks closedclosed.

The The soups remained clearsoups remained clear..Later, he Later, he broke the sealsbroke the seals & & the the soups became cloudysoups became cloudy with with microbes. microbes.

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Spallanzani’s ResultsSpallanzani’s Results

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ConclusionConclusion

CriticsCritics said sealed vials said sealed vials did not allow enough air did not allow enough air for organisms to survive for organisms to survive and that and that prolonged prolonged heating destroyed “life heating destroyed “life force”force”Therefore, Therefore, spontaneous spontaneous generation remainedgeneration remained the the theory of the timetheory of the time

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The Theory The Theory Finally ChangesFinally Changes

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How Do Microbes Arise?How Do Microbes Arise?By By 18601860, the debate had become , the debate had become so heated that the so heated that the Paris Academy Paris Academy of Sciencesof Sciences offered a prizeoffered a prize for any for any experiments that would help experiments that would help resolve this conflictresolve this conflictThe The prize was claimed in 1864 by prize was claimed in 1864 by Louis PasteurLouis Pasteur, as he published the , as he published the results of an experiment he did to results of an experiment he did to disproved spontaneous generation disproved spontaneous generation in microscopic organismsin microscopic organisms

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Louis Pasteur (1822-1895)Louis Pasteur (1822-1895)

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Pasteur's ProblemPasteur's ProblemHypothesis:Hypothesis: Microbes come Microbes come from cells of organisms on from cells of organisms on dust particles in the air; not dust particles in the air; not the air itself.the air itself.Pasteur put broth into several Pasteur put broth into several special special S-shaped flasksS-shaped flasksEach flask was Each flask was boiled and boiled and placed at various locationsplaced at various locations

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Pasteur's Experiment - Pasteur's Experiment - Step Step 11

S-shaped FlaskS-shaped FlaskFilled withFilled with broth broth The special shaped The special shaped was intended to was intended to trap any dust trap any dust particles containing particles containing bacteriabacteria

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Pasteur's Experiment - Pasteur's Experiment - Step Step 22

FlasksFlasks boiledboiled Microbes KilledMicrobes Killed

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Pasteur's Experiment - Pasteur's Experiment - Step Step 33

Flask left at various Flask left at various locationslocations Did Did not turn cloudynot turn cloudyMicrobes not foundMicrobes not foundNotice the Notice the dustdust that that collected in the neckcollected in the neck of the flask of the flask

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Pasteur's Experimental Pasteur's Experimental ResultsResults

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Pasteur’s Pasteur’s S-shaped flask kept S-shaped flask kept microbes out but let air inmicrobes out but let air in..Proved microbes only come from Proved microbes only come from other microbes (life from life) - other microbes (life from life) - biogenesisbiogenesis

The Theory of BiogenesisThe Theory of Biogenesis

Figure 1.3

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