1. Cell Theory – and the history behind it.

2. Spontaneous Generation
From pre-historic times to about 1850, most people believed that under the right conditions, living things could spontaneously appear from non-living material.

3. People throughout the Middle Ages believed that mice could be “created” spontaneously by putting grain in dark, quiet place and leaving it for a few weeks.

4. Francesco Redi Born 1626 in Italy
First to challenge the idea of spontaneous generation
Did not accept the common belief that flies magically appeared from rotting meat

5. Redi’s Experiment
IV=cover
DV=presence of flies
Hypothesis: If a jar containing rotting meat is covered, then it will produce no flies

6. Redi’s Conclusions
Flies lay eggs, which grow into maggots, which metamorphose into flies
If flies can’t lay eggs, then no new flies can grow
Fly eggs

7. Objections to Redi
Many people rejected Redi’s claim that flies do not spontaneously generate
Their reasoning:
“sealing the jar closed prevented a magical essence from entering the rotting meat and bringing it to life”
“Scientists seek only to challenge belief systems and stir things up”

8. History of Microscopes
Cells were unknown until the discovery of microscopes in the 1650’s
two scientists working independently built the first microscopes
Anton von Leeuwenhoek in Holland
Robert Hooke in England

9. Leeuwenhoek Studied pondwater, sour milk, and semen
named moving organisms “animalcules”
scared people and caused a sensation

10. - pondwater animalcules causing madness!
Leeuwenhoek’s drawings of “animalcules” set off a flurry of amateur and sometimes ridiculous claims, such as:
- pondwater animalcules causing madness!
Have pond water fro students to look at at least 8 better 16 microscopes

11. and...
Human sperm cells contain tiny human beings!
Today we can look back and think “crazy,” but at the time people took these ideas very seriously.

12. Hooke Studied cork - a kind of tree bark
named the structures he saw “cells” because they reminded him of the small rooms monks slept in.
What questions might the scientist now be asking?
Look at cork under microscope. Ask students to qenerate questions that scientist back then might now be asking

13. The discovery of cells only confused people more- If cells are alive, then where do they come from?
Can these almost invisible things appear spontaneously from the air?

14. Lazzaro Spallanzani 1729. Italian
Believed microbes that spoil food come from the air and can be killed by boiling
IV= air, DV=food spoilage
Hypothesis: If air is allowed to reach food, then microbes will get in and cause it to spoil

15. Spallanzani’s Experiment
Flask 1: boiled broth, open
Flask 2: boiled broth, sealed shut
Results
Flask 1 spoiled
Flask 2 did not spoil

16. Objections to Spallanzani
Sealing the flask shut blocked the entrance of a magical life force in the air from getting to the broth.
Since few people had seen these microbes, few people believed him.

17. Louis Pasteur
1822. France
Supported that spontaneous generation is a myth
Invented pasteurization (sterilization by heat)
Why would this be important?

18. Pasteur’s Experiment An improvement on Spallanzani’s work
Used special “swan-neck flasks” that allowed air in but kept bacteria out
IV= bacteria, DV=spoiling broth
Hypothesis; If boiled broth is kept free of bacteria, then it will not spoil even if air can reach it.

19. The curved neck allows air in but traps bacteria-carrying dust and dirt particles

20. How does what Pasteur learned keep us safe today?

21. Pasteur is the father of modern microbiology
identified yeasts as the microbes that change grape juice into wine
showed that heat can be used to sterilize foods and preserve them in sealed glass containers, and later cans.

22. The Cell Theory The cell theory has three parts:
All living things contain at least one cell
Cells are the smallest structural and functional units of life
Cells can only come from pre- existing cells

23. The cell theory-a closer look
All living things contain at least one cell
Many scientists working after Hooke and Leeuwenhoek observed different plants and animals
Each of them noted that no matter what they observed, if it was alive it had cells.

24. Development of Cell Theory
1838- German Botanist, Matthias Schleiden, concluded that all plant parts are made of cells

25. Development of Cell Theory
1839- German physiologist, Theodor Schwann, who was a close friend of Schleiden, stated that all animal tissues are composed of cells.

26. Cells are the smallest structural and functional units of life
scientists quickly realized that when cells were dissected or broken open they died
This meant that whatever “life” is, it is something that happens inside cells

27. What is Life? Living things are composed of Cells
Living things have different Levels of Organization
Living things use Energy
Living things respond to their environment
Living things Grow
Living things Reproduce
Living things Adapt/Evolve to their Environment over Time

28. Cells can only come from pre-existing cells
does not answer the question of where the first cell came from or how it came to be.
has not been disproved yet- no scientist has ever built a living cell from nonliving organic molecules

29. Development of Cell Theory
1858- Rudolf Virchow, German physician, after extensive study of cellular pathology, concluded that cells must arise from preexisting cells.

30. Modern Cell Theory
Modern Cell Theory contains 4 statements, in addition to the original Cell Theory:
The cell contains hereditary information(DNA) which is passed on from cell to cell during cell division.
All cells are basically the same in chemical composition and metabolic activities.
All basic chemical & physiological functions are carried out inside the cells. (movement, digestion, etc)
Cell activity depends on the activities of sub-cellular structures within the cell (organelles, nucleus, plasma membrane)