Chapter 1: Cells – the Basic Building Blocks of Life

Lesson 2: Historical ideas about living things Summarize some historical ideas about living things Explain how evidence can change ideas The microscope and its important role Select evidence to support or disprove ideas

Lesson 2: Spontaneous Generation From the time of Aristotle (­384–­322 BCE) to the 1600s, most people believed that many organisms (living things) came from inanimate objects (­non-living things).

Lesson 2: Redi’s Experiment In 1668, Francesco Redi set out to disprove the idea of spontaneous generation. After a few days, maggots appeared in the open jar – there were no maggots in the closed jars. Conclusion: The maggots came from flies that had got into the open jar and laid eggs, not from the meat itself.

Lesson 2: Louis Pasteur In 1864, the scientist Louis Pasteur added the same amount of boiled broth to specially designed bottles. He sealed some bottles and removed the tops from the rest, then left them for a long time. He observed no life in any of the bottles that had been sealed, but the open bottles were teeming with life.

Lesson 2: Cells With the invention of the microscope in 1590, scientists observed that living things were complex structures, which could not have possibly been formed from inanimate objects. From studying samples of cork bark, Robert Hooke discovered that organisms were made from simple building blocks. We call these individual building blocks cells

Lesson 2: Key Vocabulary and Notes Key Vocabulary: evidence, conclusion, organism, cell, microscope Key Notes: In history, people believed in the theory of spontaneous generation (living things coming from non-living things) Francesco Redi and Louis Pasteur disproved the theory using evidence from their experiments The invention of the microscope lead to detailed investigation of plants that proved living things were complex organisms made from cells

Lesson 2 : Questions and Answers 1. Do the following observations seem to support or disprove the idea of spontaneous generation? kittens coming out of a barn Ans. Support 2. Do the following observations seem to support or disprove the idea of spontaneous generation? fish swimming in a puddle 3. Do the following observations seem to support or disprove the idea of spontaneous generation? lambs being born Ans. Disprove 4. How did Redi’s experiment disprove the idea of spontaneous generation? Ans. Closed jars did not produce flies 5. What conclusions would you reach based on the evidence from Pasteur’s experiment? Ans. Life comes in from air, not non-living things 6. Which investigation would you trust the most – Pasteur’s or Redi’s? Give a reason for your answer. Ans. Pasteur because it was a more complex experiment with more evidence 7. What impact do you think microscopes have had on our understanding of living things? Ans. Living things are very complex!