Transcript The discovery of the cellular basis of living things

Patterns in Nature
Topic 2: The Discovery of the Cellular Basis of Living Things
Part of the Patterns in Nature Module
Biology in Focus, Preliminary Course
Glenda Childrawi and Stephanie Hollis
Dot Point
 Outline the historical development of the cell theory, in
particular, the contributions of Robert Hooke and
Robert Brown
kyrene.org
anbg.gov.au
Introduction
The statement that all living things are made of cells forms the
basis of what is currently known as ‘The Cell Theory’. The
historical development of the cell theory is interwoven with the
story of the invention and development of the microscope.
thebloodconnection.org
Introduction
Improvements in the design and use of microscopes as well as
progress in techniques to prepare specimens for viewing have
played a significant part in advancing our knowledge and
understanding of cells.
neato.me
Introduction
In order to better understand
where we are at today with our
understanding of life and cells, we
must first look at the historical
developments in this area.
nobelprize.org
Biological View Prior to the Cell Theory
Until the last decade of the 16th century (1590), microscopes did
not exists, cells had never been seen and so the living world had
not been considered at a cellular level.
philadelphia.about.com
Biological View Prior to the Cell Theory
One accepted view at this time was the theory of spontaneous
generation. This theory predicted that living creatures could
arise from inanimate (non-living) material.
kangaroo-protection-coalition.com
This theory is based on observation. For example, maggots ‘appeared’ on
rotting meat if it was left exposed for a period of time.
Biological View Prior to the Cell Theory
This theory was challenged in the 1500’s but it wasn’t until 1688
(nearly 2000 years later) that scientists suggested that the flies that
visited the meat contributed to the appearance of maggots.
ayerhome.co.za
This is one of the first recorded examples of experimentation being used to
oppose a theory. (an example of the scientific method)
The Invention of the compound microscope
In the late 1500’s, scientists, who were using poor quality
magnifying glasses to view small objects tried many things to
improve the images that they were viewing.
3dconceptualdesigner.blogspot.com
The Invention of the compound microscope
This led to the invention of the first compound microscope.
To get a larger and clearer image, two convex lenses could be
placed above one another. The lower lens would produce a
magnified image and the upper lens would further magnify that
image.
gloryprakash4-vibgyor.blogspot.com
The Invention of the compound microscope
Two Dutch lens makers Hans and Zacharias Janssen made the first
compound microscope in 1590. It was made of two convex lenses
placed at either end of a wooden tube. This could magnify objects
3 to 9 times!
olympusmicro.com
Technological Improvements to the
compound microscope
From there, these instruments were refined and improved upon.
By the early 1600’s most microscopes in use had a magnification of
about 30x.
sciencemuseum.org.uk
Robert Hooke in England, Anton van Leeuwenhoek in Holland and Galileo
Galilei in Italy all made noted contributions to improving the design of
microscopes
Technological Improvements to the
compound microscope
In the 17th century Robert Hooke created a compound microscope
that was progressive for its time. It had a fine adjustment and a
light source!
bicycle2011.com
The light source was a another lens that concentrated the light from a
candle onto the specimen!
Biological View: Understanding living
things using a microscope
In 1665 Robert Hooke wrote a book, the first recorded
publication to describe observations of living tissue using a
microscope: Micrographia: physiological studies of minute bodies made by
magnifying glasses
ffden-2.phys.uaf.edu
Biological View: Understanding living
things using a microscope
It was in this book that he used the term ‘cell’ to describe the
‘honeycomb’ elements of cork.
nlm.nih.gov
He was looking at dead plant cells which had no contents and would have
clearly resembled small compartments. His findings were respected but not
universally accepted at the time.
Biological View: Understanding living
things using a microscope
Anton Van Leeuwnehoek was a Dutch lens maker and was able to
produce much higher quality lenses than others. He developed a
simple microscope that used a single lens that could magnify up to
300x
findingdulcinea.com
Van Leeuwenhoek is credited with discovering bacteria and from his written
descriptions may have even seen nuclei!
Biological View: Understanding living
things using a microscope
Robert Brown is known for his discovery of the cell nucleus.
He discovered that nuclei were present in a wide variety of plant
tissue he studied.
gesneriads.ca
At the time, he had no idea of the importance of this.
Biological View: Understanding living
things using a microscope
In 1883 over a cup of coffee, two German scientists Theodor
Schwann and Matthias Schleiden were discussing the results of
their microscopic studies of living things.
merke.ch
Biological View: Understanding living
things using a microscope
As Schleiden described the regular placement of nuclei he had
observed in plant cells, Schwann recognised a similarity to the
animal cells he had been studying.
It was the first time that a common basic structure for all living things had
become evident!
Biological View: Understanding living
things using a microscope
A year later (1839) Schwann published a book on plant and animal
cells, listing three main conclusions, two of which are still
accepted today as the basis for the cell theory:
1. The cell is the unit of structure of all living things
2. The cell exists as a distinct entity and as a building block in the
construction of organisms.
3. Cells for by free-cell formation, similar to the formation of
crystals.
His third conclusion is not valid
Biological View: Understanding living
things using a microscope
In 1855 Rudolf Virchow’s studies led to the statement that ‘where
a cell arises, there a cell must have previously existed.’ From this
arose the third statement of the cell theory: All cells come from
pre-existing cells.
findabout.net
Collaboration in science: the importance of
the contributions of Hooke and Brown
The basic cell theory is today attributed to both Schleiden and
Schwann but without the work of Hooke and Brown, these two
could not have built their cell theory.
Collaboration in science: the importance of
the contributions of Hooke and Brown
The cellular basis of life was a major breakthrough in biological
thinking and led not only to further studies of cells, but also to a
cell based theory of disease.
healthmatters2day.blogspot.com
Homework
Answer the following questions in your notebook. Be prepared
to discuss next lesson.
 Explain how two areas of evidence supports the cell theory
 Identify two technological advancements which led to
advancement in the cell theory. Use an example for each
advancement