CELL THEORY AND THE DISCOVERY OF THE MICROSCOPE
Due Date: Friday 13 August 2010
References: Heinemann Science Links VELS Edition Chapter 8 (pp 186 – 207). But don’t just rely on
the textbook. You will need to consult some other references in the library or the web.
1. Construct a timeline that charts the development of the microscope and the invention of the
cell theory. Include the following scientists:
Jean Baptiste van Helmont
Robert Hooke
Rene Dutrochet
Anton van Leeuwenhoek
Francesca Redi
Matthias Schleiden
Lazzaro Spallanzani
Theodor Schwann
Louis Pasteur
Rudolf Virchow
Hans Jansen
Ernst Ruska
Zacharias Jansen
Scientist
Discovered
Date
Jean Baptiste van Helmont
Jean Baptiste van Helmont was
the first doctor to realise that
there are other gases besides
air. Helmont identified four
gases: carbon dioxide, carbon
monoxide, nitrous oxide, and
methane.
Hooke was perhaps the single
greatest experimental scientist
of the seventeenth century. His
interests knew no bounds,
ranging from physics and
astronomy, to chemistry,
biology, and geology, to
architecture and naval
technology.
It was he who discovered
bacteria, free-living and
parasitic microscopic protists,
sperm cells, blood cells,
microscopic nematodes and
rotifers, and much more. His
researches, which were widely
circulated, opened up an entire
world of microscopic life to the
awareness of scientists.
Redi set up a series of flasks
containing different meats; half
were sealed, half open. He
repeated the experiment,
replacing the sealed flasks with
gauze-covered flasks. Though
the meat in all the flasks rotted,
Redi found that only in the
uncovered flasks, which flies
had entered freely, did the
meat contain maggots.
One of the greatest advances in
diagnosis was the invention of
the compound microscope
toward the end of the 16th
century by the Dutch optician
Hans Jansen and his son
Zacharias.
Read information from the
paragraph above.
1621
Robert Hooke
Anton van Leeuwenhoek
Francesca Redi
Hans Jansen
Zacharias Jansen
1662
1668
1685
1595
1595
Lazzaro Spallanzani
Over the course of his career,
Spallanzani examined the pits
of spitting volcanoes, the world
of reproduction, the waters of
eels, the dark depths of the
bat's home, and the intricacies
of the vascular system.
1754
Matthias Schleiden
Matthias Schleiden was a
German botanist and cofounder of the cell theory.
While as professor of botany at
the University of Jena, he wrote
Contributions to Phytogenesis,
in which he stated that the
different parts of the plant
organism are composed of
cells.
A French physiologist, who
preceded Schleiden and
Schwann with similar views on
cells (1824). He stated that
growth results from both the
increase in he volume of cells
and from the addition of new
little cells. He recognized that
chlorophyll was necessary for
photosynthesis (1837).
1831
Theodor Schwann
In 1838, the botanist Matthias
Jakob Schleiden and the
physiologist Theodor Schwann
discovered that both plant cells
and animal cells had nuclei.
Based on their observations,
the two scientists conceived of
the hypothesis that all living
things were composed of cells.
In 1839, Schwann published
'Microscopic Investigations on
the Accordance in the Structure
and Growth of Plants and
Animals', which contained the
first statement of their joint cell
theory.
1839
Rudolf Virchow
Rudolf Virchow was
championed as the founder of
cellular pathology because of
his extensive research that
disease is created and
1849
Rene Dutrochet
1837
Ernst Ruska
reproduced at the cellular level
of the body.
. Through this intensive study
he recognized that focal length
of waves could be shortened by
the use of an iron cap, form this
discovery the polschuh lens was
developed, a lens used in all
magnetic high-resolution
electron microscopes
1929
2. What connection can you describe between the invention of the cell theory and the
development of the microscope? Do you think that our knowledge of cells would have developed
without the microscope?
There are numerous connections between the invention of the cell theory and the development of
the microscope. Robert Hooke discovered covered cells in a piece of cork, with his primitive
microscope, in 1663. The compound microscope was invented somewhat 68 years before Robert
Hooke looked at the piece of cork using his primitive microscope.
If any sort of microscope hadn’t been invented, we humans would have never heard or seen cells.
Cells would be completely unspecified to us. If another invention came into action instead of the
microscope we would be able to grasp the concept of cells but not fully. Everyday our knowledge on
cells continues and without the microscope we would have no awareness of the things that are in
our daily lives.
3. What was the theory of the spontaneous generation? Whose idea was it? Why did he believe it?
Who disproved this theory? How?
Several hypotheses relate to the theory of the spontaneous generation. The first serious
attack on the idea of spontaneous generation was made in 1668 by Francesco Redi, an Italian
physician and poet. At that time, it was widely held that maggots arose spontaneously in rotting
meat. Redi believed that maggots developed from eggs laid by flies. To test his hypothesis, he set
out meat in a variety of flasks, some open to the air, some sealed completely, and others covered
with gauze. As he had expected, maggots appeared only in the open flasks in which the flies could
reach the meat and lay their eggs.
Credit has been given to Francesco Redi for the theory of the spontaneous generation. Louis Pasteur
disproved the spontaneous generation. Pasteur recognised the fact that both lactic and alcohol
fermentations were hastened by exposure to air. This led him to wonder whether his invisible
organisms were always
present in the atmosphere or whether they were spontaneously generated. Pasteur was able to
prove the spontaneous theory wrong by doing this simple experiment. Pasteur was able to show
that air contained spores of living organisms. When they were placed into nutrient broth the
organisms reproduced. When he now boiled the broth in a special 'swan necked' container, that
allowed air in but kept dust out, the broth remained free of living organisms. This simple experiment
helped disproved the theory of spontaneous generation.
4. Describe and explain the Cell Theory.
The CELL THEORY, or cell doctrine, states that all organisms are composed of similar units of
organization, called cells. The concept was formally articulated in 1839 by Schleiden & Schwann and
has remained as the foundation of modern biology. The idea predates other great paradigms of
biology including Darwin's theory of evolution (1859), Mendel's laws of inheritance (1865), and the
establishment of comparative biochemistry (1940).
Ultra structural research and modern molecular biology have added many tenets to the cell theory,
but it remains as the preeminent theory of biology. The Cell Theory is to Biology as Atomic Theory is
to Physics.
Formulation of the Cell Theory
In 1838, Theodor Schwann and Matthias Schleiden were enjoying after-dinner coffee and talking
about their studies on cells. It has been suggested that when Schwann heard Schleiden describe plant
cells with nuclei, he was struck by the similarity of these plant cells to cells he had observed in animal
tissues. The two scientists went immediately to Schwann's lab to look at his slides. Schwann
published his book on animal and plant cells (Schwann 1839) the next year, a treatise devoid of
acknowledgments of anyone else's contribution, including that of Schleiden (1838). He summarized
his observations into three conclusions about cells:
1) The cell is the unit of structure, physiology, and organization in living things.
2) The cell retains a dual existence as a distinct entity and a building block in the
construction of organisms.
3) Cells form by free-cell formation, similar to the formation of crystals (spontaneous generation).
We know today that the first two tenets are correct, but the third is clearly wrong. The correct
interpretation of cell formation by division was finally promoted by others and formally enunciated in
Rudolph Virchow's powerful dictum, "Omnis cellula e cellula"... "All cells only arise from pre-existing
cells".
The modern tenets of the Cell Theory include:
1. all known living things are made up of cells.
2. The cell is structural & functional unit of all living things.
3. All cells come from pre-existing cells by division.
(Spontaneous Generation does not occur).
4. Cells contain hereditary information which is passed from
cell to cell during cell division.
5. All cells are basically the same in chemical composition.
6. All energy flow (metabolism & biochemistry) of life occurs
within cells.
As with any theory, its tenets are based upon previous observations and facts, which are synthesized
into a coherent whole via the scientific method. The Cell Theory is no different being founded upon
the observations of many. (Landmarks in the Study of Cells)
Credit for the first compound (more than one lens) microscope is usually given to Zacharias Jansen,
of Middleburg, Holland, around the year 1595. Since Jansen was very young at that time, it's possible
that his father Hans made the first one, but young Jansen perfected the production. Details about the
first Jansen microscopes are not clear, but there is some evidence which allows us to make some
guesses about them (Jansen microscopes).
In 1663 an English scientist, Robert Hooke, discovered cells in a piece of cork, which he examined
under his primitive microscope (figures). Actually, Hooke only observed cell walls because cork cells
are dead and without cytoplasm contents. Hooke drew the cells he saw and also coined the word
CELL. The word cell is derived from the Latin word 'cellula' which means small compartment. Hooke
published his findings in his famous work, Micrographic: Physiological Descriptions of Minute Bodies
made by Magnifying Glasses (1665).
5. Choose one of the scientists from the list above and describe their life and work. Include things
like where and when they were born and died, some details about their family life and information
about their scientific discoveries.
Antony van Leeuwenhoek (1632-1723)
Antony van Leeuwenhoek was an unlikely scientist. A tradesman of Delft, Holland, he came from a
family of tradesmen, had no fortune, received no higher education or university degrees, and knew
no languages other than his native Dutch. This would have been enough to exclude him from the
scientific community of his time completely. Yet with skill, diligence, an endless curiosity, and an open
mind free of the scientific dogma of his day, Leeuwenhoek succeeded in making some of the most
important discoveries in the history of biology. It was he who discovered bacteria, free-living and
parasitic microscopic protists, sperm cells, blood cells, microscopic nematodes and rotifers, and much
more. His researches, which were widely circulated, opened up an entire world of microscopic life to
the awareness of scientists.
Leeuwenhoek was born in Delft on October 24, 1632. His father was a basket-maker, while his
mother's family were brewers. Antony was educated as a child in a school in the town of Warmond,
and then lived with his uncle at Benthuizen; in 1648 he was apprenticed in a linen-draper's shop.
Around 1654 he returned to Delft, where he spent the rest of his life. He set himself up in business as
a draper (a fabric merchant); he is also known to have worked as a surveyor, a wine assayer, and as a
minor city official. In 1676 he served as the trustee of the estate of the deceased and bankrupt Jan
Vermeer, the famous painter, who had had been born in the same year as Leeuwenhoek and is
thought to have been a friend of his. And at some time before 1668, Antony van Leeuwenhoek
learned to grind lenses, made simple microscopes, and began observing with them. He seems to have
been inspired to take up microscopy by having seen a copy of Robert Hooke's illustrated book
Micrographic, which depicted Hooke's own observations with the microscope and was very popular.
Picture of Anton’s microscope; one of the many he invented.
Sir Isaac Newton is said to have claimed that he had been so successful because he had been able
to stand on the shoulders of giants. By this we think he meant that by using the work of other
scientists he was able to make his own discoveries. Do you think that the development of the
microscope and the creation of the cell theory support this idea. This is a “fat” question. You will
need to work out what Newton meant first before you can decide if this is an example to support
his thoughts.
Sir Isaac Newton said this meaning that he used the work of other experiments and inventions to
make his own discoveries. If not for the development of the microscope, Sir Isaac Newton would not
have been able to make his own discoveries. Newton invented the telescope to help you see things
better, but if not for the microscope he would not have been able to make this invention. The
telescope and microscope thing almost ties. The telescope makes you see things bigger and smaller
with a special type of glass and the microscope uses a type of glass for you to see things
microscopically.