cell discovery and theory
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History of Cell Discovery
History of Cell Discovery
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Daily Question:Brainstorm: What do you think of when you think of
the word cell?Use a circle map to brainstorm
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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
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*Leeuwenhoek
*Studied pondwater, sour milk, and other fluids
*named moving organisms “animalcules”
scared people and caused a sensation
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Leeuwenhoek’s drawings of “animalcules” set off a flurry of amateur and sometimes ridiculous claims, such as:
- pondwater animalcules causing madness!
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*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.
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Pause
Take two minutes to summarize your notes into your own words.
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*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.
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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.
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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?
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*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
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Redi’s Experiment
IV=cover
DV=presence of flies
Hypothesis: If a jar containing rotting meat is covered, then it will produce no flies
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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
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Objections to RediMany 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 brining it to life”
“Scientists seek only to challenge belief systems and stir things up”
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Pause
Take two minutes to summarize your notes into your own words.
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*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
*Lazzaro Spallanzani
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Spallanzani’s Experiment
Flask 1: boiled broth, open
Flask 2: boiled broth, sealed shut
Results
Flask 1 spoiled
Flask 2 did not spoil
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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.
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*Louis Pasteur*1822. France
Supported that spontaneous generation is a myth
*Invented pasteurization (sterilization by heat)
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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.
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The curved neck allows air in but traps bacteria-carrying dust and dirt
particles
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*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.
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Life from dead stuff= 0Biogenesis = 3
Experimental method wins out over superstition
the cell theory takes hold among ordinary people
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*Pasteur is the father of modern microbiologysupported 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.
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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...
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The Cell TheoryThe cell theory has three parts:
All living things are composed of one or more cells
Cells are the basic unit of structure and organization of all living things
Cells can only come from pre-existing cells
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*The cell theory
1. *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.
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2. *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
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*3. 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
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*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
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And now…Use Google images (select photos) to find photographs of cells.
Write a description of three cells that you see on your paper…
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Complete the Study Guide for ch 7.1If you finish early you may work on credit Option A