Emergence of the Cell Theory

1. Emergence of the Cell Theory Objectives: To understand the steps to the Research Method Critique the experiments done to challenge Abiogenesis Describe the “Cell Theory”

2. Research Method • Observation (Ask a question) • State a Hypothesis • Test the Hypothesis with a “controlled experiment” • Collect Data • Make a Conclusion • Report your Results

3. Controlled Experiments • Independent variable – (manipulated variable) • The variable being tested. • Dependent variable – (responding variable) • The effect of the variable being tested. • Experimental Part – has the variable being tested • Control part – lacks the variable being tested • Variables • Try the worksheet on HGH.

4. Let’s look at some experiments • Francesco Redi conducted an experiment to prove that maggots could not mysteriously appear on decaying meat. • Read about Redi’s first experiment on page 8 . In your notes, describe what Redi did in each of the 6 steps of the Research Method. ? • Observation (Ask a question) – • Hypothesis – • Controlled Experiment – • Data Collection (Qualitative/Quantitative)- • Conclusion • Report Results

5. Controlled Experiment

6. Redi’s Experiment • 1. Flies landed on the meat before maggots appeared. (Why do maggots appear?) • 2. If flies land on decaying meat, then maggots will appear. • 3. Set up 2 jars, one covered and one open. • 4. Open jar had maggots and the closed one didn’t. • 5. Flies lay eggs that develop into maggots. • 6. Report his results. • Redi's Experiment

7. Redi’s Experiment

8. Abiogenesis • Abiogenesis is a theory that says “living things can arise from non-living things” • First proposed by Aristotle - maggots appearing on decaying meat/recipe for mice/worms found after rain • Anton vanLeeuwenhoek invented the first microscope. His discovery fuelled the debate about where life comes from. • Read about John Needham’s experiment described on p.11. • In your notes, describe his experiment. ? • From the next slide, answer the 2 questions.

9. Needham’s Experiment • What was his conclusion ? • What mistake(s) did he make ?

10. Abiogenesis?? • Lazzaro Spallanzani recreated Needham’s experiment, but made 2 changes in an attempt to disprove his conclusion. Check out his experiment on p. 11. • What did he do ? • Why were his findings not accepted ? • What would a scientist have to do to satisfy the critics ?

11. Louis Pasteur • Pasteur came up with a way to let air in , but keep microbes out. • Read about his experiment on page 12 and describe what he did in your notes. ?

12. Pasteur’s Experiment

13. Pasteur’s Experiment

14. Pasteur’s Experiment

15. Pasteur’s Experiment • Pasteur's Experiment • Pasteur was able to reduce the variables affecting his experiment down to one…..the microbes in the air! • He disproved the Theory of Abiogenesis • It was replaced with the Theory of Biogenesis • “Only life can produce life” • Biogenesis leaves one important question unanswered? • Where did the first living thing come from???

16. Cell Theory • Robert Hooke looked at slices of cork under a microscope and saw little compartments he called Cells • German scientists Schleiden and Schwaan discovered that plant and animal tissue was composed of cells. • The Cell Theory • The cell is the basic structural component of all life • The cell is the basic functional unit of all life • Only cells can produce cells

17. Answer the questions from the worksheet titled “How Scientist’s Work”. Use the page references from you textbook to find your answers. • I’ll be checking your results