1. How their discovery led to the cell theory
Cells
How their discovery led to the cell theory

2. History
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

3. Leeuwenhoek Studied pond water, sour milk, and semen
He named moving organisms “animalcules”
He scared people and caused a sensation

4. Leeuwenhoek’s drawings of “animalcules” set off a flurry of amateur and sometimes ridiculous claims, such as:
- Pond water animalcules cause madness!

5. 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.

6. Hooke Studied cork - a kind of tree bark
He named the structures he saw “cells” because they reminded him of the small rooms monks slept in.

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

8. 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.

9. Cells are the smallest living units of matter
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

10. 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 proven wrong yet - no scientist has ever built a living cell from nonliving organic molecules.
(note the formation of an artifical living cell is yet to be confirmed –see Classjump article)

11. 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. = +

12. 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.

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. 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

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

16. Fly eggs 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

17. 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”

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

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

20. 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.

21. Louis Pasteur
1822. France
Proved that spontaneous generation is a myth
Invented pasteurization (sterilization by heat)

22. 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.

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

24. Spontaneous generation is dead!
Redi didn’t believe in it, and did an experiment using flies…..
Spallanzani didn’t believe in it, and experimented with broth….
Pasteur proved it conclusively with his open-air yet spoilage free flasks!

25. Life from dead stuff= 0 Biogenesis = 3
Experimental method wins out over superstition
The cell theory takes hold among ordinary people

26. Pasteur is the father of modern microbiology
Proved the last part of the cell theory: cells only come from pre-existing cells
Identified yeasts as the microbes that change grape juice into wine
Proved that heat can be used to sterilize foods and preserve them in sealed glass containers, and later cans.

27. Finally...
in the late 1870’s, doctors start to wash their hands and instruments before operating...some even start wearing gloves!
Joseph Lister’s wacky idea that antiseptics kill germs catches on...

28. The cell theory is one of the most important theories in biology
All living things contain at least one cell
Cells are the smallest living units of matter
Cells can only come from pre-existing cells