Thinking Like a Scientist 1.d. Think logically and use evidence

1. Biology Warm Up: Copy these assignments into your binder. Be sure to include dates and page numbersAugust 30-31WarmUp: AgendaLab: Using a Compound Microscope p29Homework: Read and take complete notes 1.1 and 1.2answer q1-5p15 DUE NEXT CLASSSeptember 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 Organization InClass: Safety Contract and quiz InClass: 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.

2. Thinking Like a Scientist1.d. Think logically and use evidence 2

3. Aristotle (384 –322 BC) • Proposed theory of spontaneous generation • Also called abiogenesis • Living things can arise from nonliving matter • Idea lasted almost 2000 years

5. Examples of Spontaneous Generation

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

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

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

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

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

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

12. Abiogenesis Recipes • Recipe for mice: Place a dirty shirt or some rags in an open pot or barrel containing a few grains of wheat or some wheat bran, and in 21 days, mice will appear. There will be adult males and females present, and they will be capable of mating and reproducing more mice.

13. Testing a Hypothesis:The controlled experiment.

14. Francesco Redi

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

16. Step 2 - Hypothesis • Rotten meat does not turn into flies. Only flies can make more flies.

17. Redi’s (1626-1697) Experiments Evidence against spontaneous generation: 1. Unsealed – maggots on meat 2. Sealed – no maggots on meat 3. Gauze – few maggots on gauze, none on meat

18. Redi’s (1626-1697) Experiments In a controlled experiment, the scientist changes only one variable, the manipulated variable. What is the manipulated variable in this experiment? 18

19. Redi’s (1626-1697) Experiments The variable the scientist, observes, measures, and records is the responding variable. What is the responding variable in this experiment? 19

20. Redi’s (1626-1697) Experiments It is called a controlled experiment because all other variables are not allowed to change. Those other variables are the controlled variables. List several controlled variables for this experiment. 20

21. Anton van Leeuwenhoek (1674) • Leeuwenhoek began making and looking through simple microscopes • He often made a new microscope for each specimen • He examined water and visualized tiny animals, fungi, algae, and single celled protozoa; “animalcules” • By end of 19th century, these organisms were called microbes

22. Anton van Leeuwenhoek 1632-1723

23. Leeuwenhoek’s Microscope

24. Needham’s Experiment

25. Lazzaro Spallanzani’s (1765) • Boiled soups for almost an hour and sealed containers by melting the slender necks closed. • The soups remained clear. • Later, he broke the seals & the soups became cloudy with microbes.

26. Spallanzani’s Results

27. Conclusion • Critics said sealed vials did not allow enough air for organisms to survive and that prolonged heating destroyed “life force” • Therefore, spontaneous generation remained the theory of the time

28. The Theory Finally Changes

29. How Do Microbes Arise? • By 1860, the debate had become so heated that the Paris Academy of Sciencesoffered a prize for any experiments that would help resolve this conflict • The prize was claimed in 1864 by Louis Pasteur, as he published the results of an experiment he did to disproved spontaneous generation in microscopic organisms

30. Louis Pasteur (1822-1895)

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

32. Pasteur's Experiment - Step 1 • S-shaped Flask • Filled withbroth • The special shaped was intended to trap any dust particles containing bacteria

33. Pasteur's Experiment - Step 2 • Flasksboiled • Microbes Killed

34. Pasteur's Experiment - Step 3 • Flask left at various locations • Did not turn cloudy • Microbes not found • Notice the dust that collected in the neck of the flask

35. Pasteur's Experimental Results

36. The Theory of Biogenesis • Pasteur’s S-shaped flask kept microbes out but let air in. • Proved microbes only come from other microbes (life from life) - biogenesis Figure 1.3