September 8, 2009• Objective: To review the steps of the

scientific method

• Do Now: (Fill in)When a hypothesis has been tested many times (and supported) it may become a __________. “If tried and true” it may become a scientific ________.

1. Do Now2. Notes on How Scientists work3. Answer 1 – 5 on p. 15

September 8, 2009• Objective: To review the steps of the

scientific method

• Do Now: (Fill in)When a hypothesis has been tested many times (and supported) it may become a __________. “If tried and true” it may become a scientific ________.

1. Do Now2. SpongeBob Scientific Method Problems

How Scientists Work

The Scientific Method and Important Experiments in Biology

Spontaneous Generation

• Years ago scientists believed many living things appeared out of nowhere

• Recipes for bees (Fig. 1-7)• Jean Baptist van Helmont in the

mid-1600s. placed a moist cloth and wheat grain inside a closed, wooden box. To his astonishment, he found a mouse nibbling at the box within a few days.

• Why do you think reasonable individuals once accepted these ideas?

Asking a Question

• People wondered how events happened (such as mice appearing from grain)

• They were identifying a problem!

• The Question– How do new living things or organisms come

into being?

Forming a Hypothesis• For centuries people accepted

that things simply arose from non-living things

• This idea or “educated guess” was given the name Spontaneous generation

• Today we consider this a hypothesis

• Many hypotheses were made and tested to disprove the original hypothesis of spontaneous generation

• Francesco Redi formed the hypothesis that flies produced maggots based on his experiences.

• He tested this hypothesis by setting up a controlled experiment!– Only one variable is changed at a time– The variable that is deliberately changed is called the

independent or manipulated variable (“I Change”)– The variable that is observed to change due to

manipulated variable is called the responding or dependent variable. (“What is Measured”)

Redi’s Experiment

• What was the Manipulated (Independent) Variable?

• What was the Responding (Dependent) Variable?

Maggots Appear NO Maggots Appear

Recording and Analyzing Results

• Scientists usually keep records of their observations and data– In this class we will keep

lab reports!!

• This is done by describing and sometimes drawing pictures of observations

• Today much of recording is done on computers

Today scientists publish their results in scientific journals such as the one pictured above.

Repeating Investigations

• NOTHING IN SCIENCE IS FACT!• Results are tested, and tested, and

tested…to ensure that they are REPEATABLE.

• Scientists are expected to test each other; this ensures that the best science is being done

• Communication is key to good science• A few scientists tested Redi’s findings…

Needham’s Test of Redi’s Findings• Hypothesized that Spontaneous Generation

could occur under the right conditions

Spallanzani’s Test of Redi and Needham’s Results

• Concluded that Needham’s test was flawed (he had not heated the broth enough) and improved upon his test

• Hypothesis was supported that only new organisms are produced from existing organisms

Pasteur’s Test

• Many scientists still argued that their were flaws in Spallanzani’s experiment (the animalcules were deprived of air).

• Pasteur designed a new flask and tested spontaneous generation• He supported his hypothesis that all living things come from other

living things.• His findings helped to convince others that spontaneous generation

was not correct.

Impact of Pasteur’s Work

• During his life Pasteur made many discoveries related to microorganisms

• He saved the French wine industry and the silk industry

• He began to uncover the nature of infectious diseases (they were the result of microorganism)

• He is considered one of biology’s most remarkable problem solvers

*Refer to pages 12 and 13 of your text for other major discoveries in biology

When Experiments Are Not Possible

• We cannot always do experiments to test a hypothesis– Ex. field studies of

animal behavior (how can you study interactions in the wild in a laboratory?)

– Ethical considerations

• What can we do when experimentation is not possible?

How a Theory Develops

• After much testing with supporting results a hypothesis may develop into a theory

• Even spontaneous generation could have been considered a theory (there was a great deal of supporting evidence)

• The hypothesis that new life comes from existing life is now considered the theory of biogenesis – meaning generating from life.

Theory

• In science the word theory applies to a well tested explanation that unifies a broad range of observations.

• They allow scientists to make accurate predictions about new situations

• It is still important to note that NO theory is considered absolute truth and as new evidence becomes available theories may be modified or thrown out completely!

QuestionsAnswer the following questions in complete sentences

(questions can be found on page 15 of text).1. Why is Redi’s experiment on spontaneous generation

considered a controlled experiment?2. How does a scientific theory compare with a scientific

hypothesis?3. How do scientists today usually communicate their

results and conclusions?4. How did the design of Pasteur’s flask help him

successfully refute the hypothesis of spontaneous generation?

5. Evaluate the impact of Pasteur’s investigations on scientists’ ideas and people’s lives.