Redi’s Experiment – Spontaneous Generation

1. Redi’s Experiment – Spontaneous Generation He was trying to disprove the idea of SpontaneousGeneration (or actually that flies came frommaggots, which camefrom flies) Francesco Redi (1668)

2. 1. Stating the Problem How do new living things come into being? • Spontaneous generation was once commonly accepted • Redi wanted to show what caused the appearance of maggots (and then flies) on meat

3. Beliefs based on prior observations(yes, these were once believed to be true) • If leaf lands on water it becomes a fish • If bale of hay left in barn it produces mice • Muddy soil gives rise to frogs • Meat hung out in the market is the source of flies

4. Belief based on prior observations • Redi observed that maggots appeared on meat a few days after flies were on meat • No microscope = no way to see eggs • But Redi believed that maggots came from eggs that were laid by flies

5. 2. Forming a Hypothesis Redi’s Hypothesis: Flies produce maggots. (he had observed that maggots came AFTER flies were on the meat)

6. Jars with meat Uncovered jars Covered jars 3. Controlled Experiment • Redi used two groups of jars • Jars that contained meat and no cover • Jars that contained meat and gauze cover

7. Uncovered jars Two groups of jars Covered jars Control and Experimental Groups • used as a standard of comparison • the group containing the factor (variable) that has been changed Control group: Experimental group: (manipulated or independent variable)

8. Setting up a Controlled Experiment In a controlled experiment, only one factor is changed at a time. • Independent (manipulated) variable: the factor that is deliberately changed • Dependent (responding) variable: the factor that the scientist wants to observe; it changes in response to the independent variable

9. Variables in Redi’sExperiment • Controlled Variables: jars, type of meat, location, temperature, time • Manipulated Variables: gauze covering that keeps flies away from meat

10. Two groups of Jars with meat Uncovered jars Covered jars Let’s think about this.… • Which is the control group? • Which is the experimental group? Uncovered jars (left) Covered jars (right)

11. Redi’s Experiment on Spontaneous Generation OBSERVATIONS: Flies land on meat that is left uncovered. Later, maggots appear on the meat. HYPOTHESIS: Flies produce maggots. PROCEDURE Covered jars Uncoveredjars Controlled Variables: jars, type of meat, location, temperature, time Several days pass Manipulated Variables: gauze covering that keeps flies away from meat Responding Variable: whether maggots appear Maggots appear No maggots appear CONCLUSION: Maggots form only when flies come in contact with meat. Spontaneous generation of maggots did not occur.

12. 4. Collect and Record Data observations and measurements made in an experiment Data: Types of Recorded Data • Quantitative - observations that involve measurements/numbers; i.e. 3 days, 12 maggots, 4 g, 13 sec • Qualitative - observations thatdo not involve numbers, are of a descriptive naturei.e. white maggots covered the meat, leaves were all wilting

13. 4. Analyze the Data • Create & examine data tables, charts, and graphs • Examine experimental notes • Look for trends, patterns, and averages • What does the data show? • Put your data into words

14. 5. Draw Conclusions • Restate the hypothesis: Example: Flies produce maggots. • Accept or reject the hypothesis. • Support your conclusion with specific, numerical data. • What was Redi’s conclusion? • Flies lay eggs too small to be seen. • Maggots found on rotting meat are produced from the eggs laid by flies. • Maggots are not appearing due to spontaneous generation!

15. 6. Publish Results Communication is an essential part of science • Scientists report their results in journals, on the internet, or at conferences • This allows their experiments to be evaluated and repeated • Scientists can build on previous work of other scientists Redi’s experiment on insects generation