biology 2201 ch 1.1 notes.notebook
October 08, 2011
Biology 2201
1.1 – Historical Development of Cell Theory
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Development of the Cell Theory
• People have known about the
existence of cells for only the
last 300 yrs or so
•
• Early microscopes allowed
scientists to discover what we
now take for granted:
Onion skin cells
• All living things are made up of cells
• Cells are fundamental units of life
Paramecium
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biology 2201 ch 1.1 notes.notebook
October 08, 2011
Cell Theory
• In a sense, all biology is based on the fact that all
living things are made up of units called cells. As
well, these cells are the functional units of an
organism.
• Cell Theory
• 1. all living things are made up of one or more cells
• 2. cells are the basic units of structure and function in all
organisms
• 3. all cells come from pre-existing cells
• 4. in a multicellular organism, the activity of the organism
depends on the total activity of its independent cells
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Going Back A Few Years
• Cell theory was stated first in 1858, challenging
the believe system at the time
• People believed small animals could arise
spontaneously from non-living or dead things
• “Spontaneous Generation”
• Thomas Huxley renamed it to “abiogenesis”
• Live coming from life came to be called
“biogenesis”
Thomas Huxley
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biology 2201 ch 1.1 notes.notebook
October 08, 2011
Abiogenesis vs. Biogenesis
• Before the development of cell theory in
1858, the idea that living things could only
come from other living things was not
believed. Many people felt that some living
things could come from non-living things.
• Abiogenesis (spontaneous generation): the
idea that living things can come from nonliving things
• Biogenesis: the idea that living things can
only come from other living things
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Evidence for Abiogenesis
Evidence that supported abiogenesis
Fact or Fiction
Fiction – Maggots were present, but only after the Maggots suddenly appeared on uncovered meat after several days flies laid their eggs on the meat
Frogs and salamanders suddenly appearing on or in mud
Fiction – These amphibians hibernate and burrow into the mud and come to the surface to eat
Jan Baptista van Helmont said that Fiction – The mice that were attracted to the food source ﴾wheat﴿ arrived, and then mated. They mixing a dirty shirt with wheat possibly hid in the mixture
grains would produce adult mice that would then mate.
John Needham’s experiment with meat broth teeming with microbes after being boiled.
Fiction – He did not boil the broth long enough to kill all the bacteria in the broth, and so they divided, making the broth cloudy.
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biology 2201 ch 1.1 notes.notebook
October 08, 2011
Key Events in Biological History
• Aristotle observes and
formulates ideas about nature.
• He was the first to divide organisms
into two groups (kingdoms)
• Plants – those that don’t move
• Animals – those that move
• Aristotle supported spontaneous
generation.
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More History
• After studying the nature of reproduction, William
Harvey begins to question the idea of abiogenesis,
suggesting that maggots on meat come from eggs that
are too small to see. This was during the 1600’s, and we
now know this to be true
•
• Robert Hooke writes a book, in which it shows
illustrations of tree bark as seen under the microscope.
The drawing showed compartments he called “cells”
•
• Antony van Leeuwenhoek designed his own
microscope with a tiny simple lens. He reported that he
seen tiny “animalcules” or tiny organisms that moved.
This marked the discovery of bacteria, the simplest of
all living organisms. Leeuwenhoek developed
microscopes that had the clearest quality image at the
time.
Bark cells
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biology 2201 ch 1.1 notes.notebook
October 08, 2011
Francesco Redi
• Conducted one of the first controlled experiments that supported
biogenesis. He used meat in jars, half covered with mesh and half open. After
several days he found that the mesh-covered meat had no maggots, while the
open jar had maggots.
• See page 8 in textbook
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Needham & Spallanzani
• John Needham designed and experiment that incorrectly supported abiogenesis. He
boiled a meat broth for a short period of time, and poured it into two flasks, covered
and uncovered. Both became cloudy because of bacterial growth after several days. He
believed that the organisms came from the water itself. He did not boil the water long
enough to kill all the bacteria.
•
• Lazzaro Spallanzani didn’t agree with Needham, and so repeated Needham’s
experiment. This time the broth was boiled for a longer time. No life appeared in the
sealed flask, while the open flask had bacterial growth. Boiling the broth “killed the vital
principle” that made life arise from non-living matter like water.
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biology 2201 ch 1.1 notes.notebook
October 08, 2011
Other Scientists
• Robert Brown observed cells from various organisms and noticed that they all
had a dark region in them. This dark region has recently been called the nucleus.
•
• Matthias Jacob Schleiden, a botanist, said that “all plants are made up of cells”
•
• Theodor Schwann wrote that “all animals are made up of cells” and then added
that “cells are organisms, and animals and plants are collectives of these organisms”
•
• Alexander Carl Henrich Braun said “cells are the basic unit of life”
• Jugo von Mohl said that “protoplasm is the living substance of the cell” then
added that “cells are made up of protoplasm enveloped by a flexible membrane”
• Rudolph Virchow wrote that “cells are the last link in a great chain [that forms]
tissues, organs, systems and individuals… where cells exist there must have been
pre-existing cells…”
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Louis Pasteur
• conducted experiments that
disproved abiogenesis,
concluding that organisms do
NOT arise from non-living
matter.
• Goose-neck flask experiment
is the guiding principle behind
pasteurization
Pasteur’s Experiments
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