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The Development of the
Cell Theory
Cell Biology
Prepared by: A. Abougabal
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Ancient Times• Ancient peoples are
always on the look-out for ways that organisms can be used by them.
• Some civilizations support “great thinkers” and philosophers, but they rarely base their thoughts on observation or experiments.
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Timeline of the discoveries, thoughts and technologies that led to the development of the Cell Theory
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334 B.C.E - Aristotle
• Greek philosopher, Aristotle, begins to observe nature.
• He classifies all known organisms as either a Plant or and Animal.
• He writes that living things can arise spontaneously from non-living matter.
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1268 – 1st Eyeglasses
• Roger Bacon, an English friar makes reference to a pair of eye glasses.
• This means that glass is being developed and used in a way that makes it easier to see small things.
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Timeline of the discoveries, thoughts and technologies that led to the development of the Cell Theory
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1590 – 1st Microscope
• Zacharias Janssen, a Dutch eyeglass maker, makes the 1st microscope by placing two lenses on top of one another to make extra-large images.
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Timeline of the discoveries, thoughts and technologies that led to the development of the Cell Theory
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1600’s
• People start to question the origins of life.
• Many begin to suggest that life can only come from other forms of life rather than through spontaneous generation (as was suggested by Aristotle). This only took about 2000 years!
• William Harvey says that maggots do not come from the meat itself but from tiny eggs too small to be scene.
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Timeline of the discoveries, thoughts and technologies that led to the development of the Cell Theory
William HarveyEnglish Physician
1578-1657
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Cell Theory and the Scientists Who Helped
Shape It
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• Anton van Leeuwenhoek (1632-1723) reports being able to see tiny beasties (0.002 mm) using a simple single-lens microscope.
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1674 – 1st Microscopic Beasties Seen!
He is known as the
“Father of microscopy.”
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Anton van Leeuwenhoek
he documented unicellular organisms based on observations of protozoa [1673] and bacteria
[1683]
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Robert Hooke• Born: July 18, 1635
• Died: March 3, 1703
• Wrote and published “Micrographia”
• Known as the
“English Father of
microscopy”http://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Hooke.html
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Robert HookeContributions:– [1665] He observed
pieces of cork from the bark of a cork tree under the microscope.
– His observations led him to coin the word “cell.” -“Cell” means little rooms in Latin
http://www.learner.org/channel/courses/essential/life/session1/closer1.html
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1667 – Species Defined
• John Ray (1627-1705) defines a “species” as a set of individuals that can reproduce their own kind.
• The beginning of the end of spontaneous generation!
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Timeline of the discoveries, thoughts and technologies that led to the development of the Cell Theory
William HarveyEnglish Physician
1578-1657
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• Francesco Redi (1626-1697) conducts experiments to prove that maggots do not appear in meat if flies cannot land on it!
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Timeline of the discoveries, thoughts and technologies that led to the development of the Cell Theory
William HarveyEnglish Physician
1578-1657
1668 – 1st Experiments about origins of maggots
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• Microscope claimed to be an instrument of evil when a prominent person was horrified by the sight of a magnified flea!
• Scientists begin to doubt spontaneous generation, but the common people still believe in it!
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1700’s
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• Microscopes become sturdier and easier to use.
• Flaws in glass production still causes images to be blurry and have coloured halos.
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1770 – Advancement of microscopes
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• Jane Haldimand (1769-1858) writes textbooks for young people to learn about science.
• Terms such as
“cell”, “cellular system” and “Cellular tissue” appear in the book.
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Timeline of the discoveries, thoughts and technologies that led to the development of the Cell Theory
1809 – 1st Science Texts for Students
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• Francois Vincent Raspail (1794-1878) wrote a book called (translated from Latin)
“Every cell is derived from a pre-existing cell”.This again puts to rest the idea of spontaneous generation.
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Timeline of the discoveries, thoughts and technologies that led to the development of the Cell Theory
1825 – Book “Cells from Cells”
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• Biology is becoming an important science and the body of knowledge is growing, especially since the improvement of microscopes.
• Scientists begin to study the cell extensively!
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1830 – Cells are studied
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• Robert Brown (1773-1858) is the 1st to consider the nucleus as a regular part of a living cell.
• The nucleus is still hard to see though without the invention of the electric light for his microscope.
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Timeline of the discoveries, thoughts and technologies that led to the development of the Cell Theory
1831 – Nucleus of Cell Found
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• Matthias Jacob Schleiden (1804-1881) makes the claim “All plants are made of cells”.
• Cells are alive!
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1838 – Plant cells!
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• Theodor Schwann (1810-1882) makes the claim “All animals are made of cells”.
• “All living things are made of cells”
• Cells are the basic building blocks of life!
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1839 – Animal cells!
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• Alexander Carl Heinrich Braun (1805-1877) makes the claim:
“The cell is the basic unit of life”.
• Cells are made of protoplasm enveloped by a flexible membrane.
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1845 – Cell Basic Unit of Life
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• Louis Pasteur (1822-1895)
• conducts a series of experiments that once and for all put to rest the idea of spontaneous generation and concluding that living organisms do not arise from non-living matter.
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Timeline of the discoveries, thoughts and technologies that led to the development of the Cell Theory
1860’s, The end of the “Spontaneous Generation” debate
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Who came up with the theory?
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• Major Contributors:
• Matthias Schleiden• Theodor Schwann• Rudolph Virchow
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1-Rudolph Virchow
• German pathologist
• He is known as the
“Father of Pathology.”
Born: October 13, 1821Died: September 5, 1902
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Rudolph wirchow stated “omnis cellula a cellula ” [all cells arise from pre-existing cells based on observations of dividing
cells [1855] All cells come from
pre-existing cells!
Virchow
• Cell Theory
• that is still largely accepted today.
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2. Schleiden (1838) All plants are made of cells!
Onion skin cells
German botanist
Born: April 5, 1804Died: June 23, 1881
proposed that cells were the fundamental units of plants based on observations of plant tissue [1838]
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Plant cells
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3. Schwann
Who came up with this theory?
All animals are made of
cells!
Human red blood cells
proposed that cells were the fundamental units of animals based on observations of
animal tissue [1839]
Born: December 7, 1810Died: January 11, 1882
/
• German zoologist
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Blood
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Sperm
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Schleiden and Schwann
The Cell Theory [1839]• All living things are made of
cells.
• Cells exhibit the fundamental characteristics of life:– Obtain energy—photosynthesis, chemosynthesis, or digestion
– Use energy—respire
– Excrete Waste
– Show Order
– Homeostasis
– Evolve
– Reproduce
– Move
– Respond to changes in environment
– Grow and repair damage to self
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The Cell Theory States:• As written by Rudolph Virchow (1821-
1902):– All living organisms are made of one
or more cells.
– Cells are the basic units of structure and function in all organisms.
– All cells come from previously existing cells.
– The activity of an entire organism depends on the total activity of its independent cells.
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Definition
= Three part theory about cells
1. All living things are made of cells.
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Part 2 of the Theory
2. The cell is the basic structural and functional unit of life.
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Part 3 of the Theory3. All cells come from pre-existing
cells.
yeast cells dividing
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How big are cells?• Microscopic
(mostly)• Measured in
microns µm • (micrometers).
• A µm is one millionth of a meter =
• 10-9 m = one thousandth of 1 mm.
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How big are cells?
Smallest free-living cell = Mycoplasma genitalium
Size = 0.2 to 0.3 µm
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How big are cells?• Bacteria e.g. Eschericia coli (aka
E.coli)
• Size=1 µm by 3 µm
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How big are cells?• Human red blood cell =
• 8 µm in diameter
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How big are cells?
• Largest cell on the human body
= ovum
• Size=
• 1000 µm in diameter
(1 mm)
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How big are cells?• Smallest cell in the human body =
sperm cell.
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How can we study cells?
Problem:
They are microscopic!
Solution:
Use a microscope!
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Cell biology• Cell biology is the study of cell structure and
function, and it revolves around the concept that the cell is the fundamental unit of life.
• Focusing on the cell permits a detailed understanding of the tissues and organisms that cells compose.
• Some organisms have only one cell, while others are organized into cooperative groups with huge numbers of cells.
• On the whole, cell biology focuses on the structure and function of a cell, from the most general properties shared by all cells, to the unique, highly intricate functions particular to specialized cells.
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Microscopes
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1. Compound light microscope
– Light passes through lenses to magnify image up to 1000X
– Can observe living cells
A. COMPOUND MICROSCOPE
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Light Microscope
Human Cheek Cell Nerve Cells
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B. STEREOMICROSCOPE
• Gives 3D images of specimen
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C. SCANNING ELECTRON MICROSCOPE (SEM)
1. Uses electrons instead of light to project surface image of specimen
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SCANNING ELECTRON MICROSCOPE (SEM)
2. Electron microscope
– Uses a beam of electrons to magnify image
> 1000X– Kills cells being
observed
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Scanning Electron Microscope
Human Sperm Insect Head
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D. TRANSMISSION ELECTRON MICROSCOPE (TEM)
1. Works like light microscope except uses electrons
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Transmission Electron Microscope
Plant Cell Mitochondrion
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Comaparison of Light and Electron Microscopes
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Microscopic measurementsmm – millimeters
μm – micrometer
nm - nanometers
1m = 1000mm = 1000,000μm= 1000,000,000nm
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Assignment #1 which microscope can be
used to study the following Sizes of Biological Structures
• Thickness of leaf• Paramecium• Sharp end of pin• Plant cell• Animal cell• Mitochondrion• Bacterium• Ribosome• DNA molecule• Hydrogen atom
• O.5mm
• 200μm
• 100 μm
• 40μm
• 20μm
• 1μm
• 0.5-1μm
• 20nm
• 2nm
• 0.04nm
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And, what about viruses?• Are not composed of cells
but consist of a nucleic acid (DNA or RNA) in a protein coat
• Yet conduct all of the cell processes (although with help, not independently)