1. Cells and The Cell Theory

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

3. Robert Hooke in 1665 - First to coin term – “Cell” Looked at Cork
Looked really at a dead plant cell
Only saw the cell wall

4. Anton Van Leeuwenhoek 1600’s Made lenses that could magnify more.
Observed many living organisms
Looking at Protists called them “Wee Beasties” or “animalcules” (small animals)

5. Anton Van Leeuwenhoek
Leeuwenhoek’s drawings of “animalcules” set off a flurry of amateur and sometimes ridiculous claims, such as:
- pondwater animalcules causing madness!

6. Anton Van Leeuwenhoek -- looked at pond scum
-- looked at blood from different animals
-- looked at tartar from teeth
-- first person to see bacteria
--discovered yeast is a unicellular organism
(yes….yeast found is bread is a living thing!)

7. Birth of the cell theory…
1838 Matthias Schleiden – concludes all plants made up of cells
1839 – Theodore Schwann concludes all animals are composed of cells
Wrote 1st two parts of cell theory.

8. Birth of the cell theory…
1858 Rudolph Virchow – discovered that cells could not develop from anything except other cells
Wrote the third part of the Cell Theory.

9. The Cell Theory The cell theory has three parts:
All living things contain at least one cell (Schwann)
The cell is the basic unit of life (Schwann)
Cells can only come from pre-existing cells. (Virchow)

10. All living things contain at least one cell
The Cell Theory
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.

11. Cells are the smallest living units of matter
The Cell Theory
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

12. Cells can only come from pre-existing cells
The Cell Theory
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

13. 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

14. All cells have the following in common:
Cell Similarities
All cells have the following in common:
1. Cell Membranes
-surrounds the cell
-barrier between inside of cell and environment
-controls the passage of materials through the cell
2. Hereditary Material
-DNA
-controls activities of the cell
-contains the info needed to make new cells

15. All cells have the following in common:
Cell Similarities
All cells have the following in common:
3. Cytoplasm and Organelles
-organelles = structures that allow the cell to live,
grow, and reproduce.
-cytoplasm = the fluid inside a cell that surrounds
the structures.
4. Small Size

16. Benefits of Being Multicellular
Grow by producing more small cells, not larger cells.
Can perform more functions than unicellular.
Many kinds of cells
A single cell cannot do all the things that many different things that cells can do.

17. 1. Prokaryotic Cells Two Types of Cells AKA = Bacteria
World’s smallest cells
NO NUCLEUS!
DNA is on long, circular molecule (rubber band)
Organelles do not have membranes
Have ribosomes (to make protein)
Most have a hard cell wall
Probably the first type of cells on Earth.
Oldest fossils ever found (3.5 billion yrs ago)

18. 2. Eukaryotic More complex than prokaryotic 10 times larger
Fossil evidence (2 billion yrs ago)
All living things (except bacteria) have eukaryotic cells
Have a nucleus
All have cell membrane
Some have cell wall
Organelles have membranes
Have more DNA than prokaryotic
DNA stored in nucleus
DNA molecules are linear (not circular)

19. Prokaryotic vs. Eukaryotic
No nucleus
Nucleus
Organelles = no membranes
Organelles = have membranes
DNA = circular
DNA = linear (line)
Bacteria
All other cells

20. 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.

21. 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.

22. 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?

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

24. Redi’s Experiment
Independent variable = cover
Dependent variable = presence of flies
Hypothesis: If a jar containing rotting meat is covered, then it will produce no flies

25. 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

26. 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”

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

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

29. 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.

30. Louis Pasteur
1859. France
Supported that spontaneous generation is a myth
Invented pasteurization (sterilization by heat)

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

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

33. 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 disproved it conclusively with his open-air yet spoilage free flasks.

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

35. Pasteur is the father of modern microbiology
supported 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
showed that heat can be used to sterilize foods and preserve them in sealed glass containers, and later cans.

36. 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...

37. 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