Cells and The Cell Theory
Dec 18, 2015
Cells and
The Cell Theory
Cells and
The Cell Theory
Anton von Leeuwenhoek
in Holland
Robert Hooke in
England
Cells were unknown until the invention of microscopes in the
1650’s
two scientists working independently built the first microscopes
Anton Van Leeuwenhoek
1600’s
Made lenses that could magnify more.
Observed many living organisms
Looking at Protists called them “Wee Beasties”
Anton Van Leeuwenhoek
Leeuwenhoek’s drawings of “animalcules” set off a flurry of amateur and sometimes ridiculous claims, such as:
- pondwater animalcules causing madness!
Anton Van Leeuwenhoek
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.
Robert Hooke
in 1665 - First to coin term – “Cell”
Looked at Cork
Looked really at a dead plant cell
Only saw the cell wall
Late 1800’s – Charles Spencer developed the modern day compound light microscope
Can magnify an object up to 1000 times!
Scientists start looking at everything under the microscope and they notice…
Every living thing seems to be made up of small units called cells!
1838 Matthias Schleiden – concludes all plants made up of cells
Birth of the cell theory…
1839 – Theodore Schwann concludes all animals are composed of cells
Birth of the cell theory…Schleiden & Schwann, in 1839, formally espoused cell theory –
Cells are of universal occurrence in living things
and
Cells are the basic units of an organism
Birth of the cell theory…In 1858, Rudolph Virchow forcefully states the paradigm of cell theory
``All cells come from previous cells’’Omnis cellula e cellula
Thus: all individuals derived from a single celled organism are related
and all cells in a multi-celled organism are descended from one fertilized egg.
The Cell TheoryThe 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
The Cell TheoryAll 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.
The Cell TheoryCells 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
The Cell TheoryCells can only come from pre-existing
cellsdoes 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
Spontaneous GenerationFrom pre-historic times to about 1850, most people believed that under the right conditions, living things could spontaneously appear from non-living material.
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.
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?
Francesco Redi
Born 1626 in Italy
First to challenge the idea of spontaneous generation or biogenesisDid not accept the common belief that flies magically appeared from rotting meat
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
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
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”
Lazzaro Spallanzani1729. Italian
Believed microbes that spoil food come from the air and can be killed by boiling
Independent variable = air
Dependent variable = food spoilageHypothesis: If air is allowed to reach food, then microbes will get in and cause it to spoil
Spallanzani’s ExperimentFlask 1: boiled broth, open
Flask 2: boiled broth, sealed shut
Results
Flask 1 spoiled
Flask 2 did not spoil
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.
Louis Pasteur1859. France
Supported that spontaneous generation is a myth
Invented pasteurization (sterilization by heat)
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.
The curved neck allows air in but traps bacteria-carrying dust and dirt
particles
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.
Life from dead stuff= 0Biogenesis = 3
Experimental method wins out over superstition
the cell theory takes hold among ordinary people
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.
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...
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