Ask a Question Form a hypothesis Set up a controlled

experiment Record and

analyze results Draw a Conclusion Repeat

The goal of science is to investigate and understand the natural world, to explain events in the natural world, and to use those explanations to make useful predictions.

Should you just accept an explanation for something?

2,000 years ago, a Roman Poet wrote a Recipe for Bees› 1. Kill a bull› 2. Build a shed› 3. Place dead bull on

branches inside shed› Wait for summer.

Decaying body will produce bees

A hypothesis is a scientific explanation for a set of observations that can be tested in ways that support or reject it.

Hypotheses are not always correct!› Spontaneous Generation

Life can arise from non-living things

“Vital forces” bring living things into being from non-living things

Italian physician (born 1626) Set up an experiment to disprove the theory

that maggots came from decaying meat (spontaneous generation)

OBSERVATIONS: Flies land on meat that is left uncovered. Later, maggots appear on the meat.

HYPOTHESIS: Flies produce maggots.

PROCEDURE

Controlled Variables:jars, type of meat,location, temperature,time

Manipulated Variables:gauze covering thatkeeps flies away from meat

Uncovered jars Covered jars

Several days pass

Maggots appear No maggots appear

Responding Variable: whether maggots appear

CONCLUSION: Maggots form only when flies come in contact with meat. Spontaneous generation of maggots did not occur.

Section 1-2

Figure 1-8 Redi’s Experiment on Spontaneous Generation

Variables must be controlled› Change only one thing at a time› Ex – one jar covered and one uncovered

Controls are the parts of the experiment that are the same› Ex: types of jars,

type of meat, temperature

The part of the experiment that changes› Ex: covered and uncovered

jars› Also known as independent

variable

What happens as a result of the manipulated variable

The result of the experiment

Also know as dependent variables

Detailed and specific Use notebooks, journals, computers

› Redi kept a journal so others copying his work could see his results

Scientists record experimental observations, gathering information called data. There are two main types of data: quantitative data and qualitative data.

Quantitative data are numbers obtained by counting or measuring.

Qualitative data are descriptive and involve characteristics that cannot usually be counted.

5 qualitative observations about the classroom

5 quantitative observations about the classroom

Did your results support or refute your hypothesis?

Redi proposed that flies produce maggots not the rotting meat…was he right?

If data does not support your hypothesis, you must come up with a new hypothesis and re-test.

Scientists must be able to repeat each other’s investigations AND get the same results to ensure they are valid

Anton von Leeuwenhook› Saw “animalicules” in pond water, rainwater

and dust› Said spontaneous generation could occur

John Needham› Used

“animalicules” and gravy to show spontaneous generation could occur (p. 11)

› What was wrong with his experiment?

Heated gravy, looked at it days later and saw “little animals”

Improved Needham’s experiment Believed Needham did not heat the gravy

to kill everything

Gravy is boiled.Flask isopen. Gravy is teeming

with microorganisms.

Gravy is boiled. Flask issealed.

Gravy is free of microorganisms.

Section 1-2

Figure 1-10 Spallanzani’s Experiment p. 11

Organisms had to enter the flask from the air since sealed container was free of microorganisms

Supported Redi, Disproved Needham

Some people said Spallanzani’s experiment wasn’t fair because it eliminated air from one of the flasks› Thought air was the “life force” needed to

produce new life

Designed a new flask and repeated Spallanzani’s experiment

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Broth is boiled. Broth is free ofmicroorganismsfor a year.

Curved neckis removed.

Broth is teeming with microorganisms.

Section 1-2

Figure 1-11 Pasteur’s Experiment

Broth is boiled. Broth is free ofmicroorganismsfor a year.

Curved neckis removed.

Broth is teeming with microorganisms.

Section 1-2

Figure 1-11 Pasteur’s Experiment

Broth is boiled. Broth is free ofmicroorganismsfor a year.

Curved neckis removed.

Broth is teeming with microorganisms.

Section 1-2

Figure 1-11 Pasteur’s Experiment

Broth is boiled. Broth is free ofmicroorganismsfor a year.

Curved neckis removed.

Broth is teeming with microorganisms.

Section 1-2

Figure 1-11 Pasteur’s Experiment

Convinced scientists spontaneous generation was false

Explained the souring of wine

Discovered small organisms were responsible for disease.

Animal studies – observe only Exposure to certain chemicals causing

cancer› Can’t give people a chemical you suspect

causes cancer

A well tested explanation that unifies a broad range of observations

Can you name some http://www.biologycorner.com/worksh

eets/scientific_method_plant_exp.html#.UjsFM2fpWSo