Biology 2201
Unit 1 - Matter and Energy for Life
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Biology is the study of Life
What does this mean, “Life” or “Living”?
The Cell
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The cell is the basic unit of life in which all
living things are composed of one or more.
The cell is the smallest unit capable of
displaying the characteristics of life.
These two ideas are central to the Cell
Theory.
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It may be suprising that although the cell is of
great importance to life, it was only discovered
quite recently in human history. Some 300 years
ago.
The Cell Theory
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The cell theory is formulated from four main
hypothesis.
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1. All living organisms are composed of one or more cells
2. Cells are the basic units of structure and function in all
organisms.
3. All cells are derived from pre-existing cells.
4. In a multicellular organism, the activity of the entire
organism depends on the total activity of its independent
cells.
The cell theory was first stated in 1858.
Early Cell Biologists
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For Centuries Scientific knowledge was based on
simple observations instead following the scientific
method. (World was flat, earth was center of
universe, etc...)
One such idea, since the time of Aristotle, was that
living things could arise from mud, dust, water. This
idea was referred to as Spontaneous Generation
was renamed Abiogenesis in 1870 by the British
scientist Thomas Huxley
Opposite to this thought were those that believed in
Biogenesis. That life could only originate from life.
Paradigm Shift
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Aristotle, the Greek philosopher (384-322 B.C.E.)
Seeks answers to questions through observation
and thought and not through experimentation.
1590's Dutch eyeglass makers create the first
compound microscope by lining up two lenses.
1600's debates rage over the nature of reproduction.
Most still believe in Abiogenesis, but one British
physician held strong beliefs that life only came from
life.
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1665 - an English scientist Robert Hooke
published, ‘Micrographia’. The first book to
show sketchings of once living objects
through a microscope. He saw little roomlike compartments that he called “cells”.
1666-67 - Dutch, Antony van Leeuwenhoek
read Hooke’s book and designed his own
microscope with magnification unlike any that
had been created.
1668 - Italian, Francesco Redi conducts one
of the first controlled scientific experiements
to disprove the Abiogenesis theory.
Redi’s Experiment
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Redi placed rotting meat in two separate jars.
The control group was left alone with no
cover.
The experimental group was sealed with a
cloth over the top.
Over time the control group jar filled with
maggots and flies and the experimental jar
was free of all insects. This validated his
hypothesis that flies arise from other flies.
Leeuwenhoek Discoveries
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1673 - Leeuwenhoek begins writing letters to
the Royal Society that continued for 50 years.
In one letter he reports observing tiny
‘animalcules’ in standing water.
1683 - Leeuwenhoek examines the plaque
from his wifes and daughters teeth and
observed, “many very little things prettily amoving.” This was the first observation of
bacteria.
Needham vs Spallanzani
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Case of the Mystery Meat
1748 - an English naturalist and priest, John
Needham designs an experiment to support
Spontaneous generation.
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Needham brings meat broth to a boil for a short
time to sterilize it. He then pours broth into two
jars. One jar is left open the other is sealed.
Within days both jars were filled with microorganisms.
Spallanzani’s reply
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Lazzaro Spallanzani is skeptical of
Needham’s results so follows Needham’s
procedure, but boils the broth for a longer
period of time.
No microorganisms appear in the sealed jar.
Supporters of Spontaneous generation
argued that too much boiling killed some ‘vital
principal’ needed for life to arise.
Paradigm cont.
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1830 - biology is evolving into a major body
of knowledge and microscopes are improving
1831- Scotish scientist Robert Brown
identifies the cell nucleus.
1838-39 Schleiden and Schwann make the
statements, “all plants are made of cells” and
“all animals are made of cells” respectively.
1845 - Henrich Braun writes, “The cell is the
basic unit of life.”
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1856 - English chemistry student William Henry
Perkin develops an intense purple dye that can stain
slide specimens.
1858 - German physiologist Rudolph Virchow
writes, “Cells are the last link in a great chain
...tissues, organs, systems, and individuals... Where
a cell arives from a preexisting cell.
1860 - French biologist Louis Pasteur ends the
debate with a scientific experiment to disprove
spontaneous generation. Pasteur’s swam neck
flask finally showed that micro-organisms came from
other micro-organisms in the air and water, and not
by spontaneous generation.