Place homework assignment 1-3 in the black basket. Place returned welcome letter stub in the silver basket. Place student information sheet next to the baskets. Pick up a copy of the powerpoint guide.

Scientific Investigation

1. Scientific investigation begins with a problem or an initial question or observation.

Question: How do new living things, or organisms, come into being?

Spontaneous Generation Supposed appearance of living things from nonliving matter.

The Hypothesis Francesco Redi Challenges Spontaneous Generation Redi proposes a hypothesis: Maggots come from the flies not from the meat. A hypothesis must be a testable statement in response to the initial question.

Experimental Design Redi Designs the following experiment. Controlled or uncontrolled?

A controlled experiment is one in which only one variable is changed and there is a standard of comparison. Independent (manipulated) variable is a variable deliberately changed by the person conducting the experiment. Dependent (responding) variable is the variable that changes in response to the manipulated variable.

What was Redi’s control group?...experimental group? What was the independent variable? What was the dependent variable?

Recording and Analyzing Results Scientists keep records of their data and observations. Redi’s results were available to later generations.

Drawing a Conclusion Evidence against spontaneous generation: 1. Unsealed – maggots on meat 2. Sealed – no maggots on meat 3. Gauze – few maggots on gauze, none on meat

Conclusion A conclusion must be supported by evidence. Was the hypothesis supported or refuted? Redi’s results could be viewed as an explanation about maggots and flies and also a refutation for the hypothesis of spontaneous generation.

Inference – A conclusion made on the basis of facts rather than observations.

Inference

Theory A broad and comprehensive statement of what is thought to be true. A theory may be tested again and again. Examples: evolution, germ theory

Or have we?