THE CELL
THEORY
© 2007 Paul Billiet ODWS
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Objectives:
 Outline
the main principles of cell theory.
 Discuss the evidence for cell theory.
 State that unicellular organisms carry out all
the functions of life.
 Appreciate the relative sizes of biological
structures.
What level of complexity is
necessary for life?
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Aristotle (384 – 322BC)
http://tw.youtube.com/watch?v=Tm0Uq08xXhY
© 2007 Paul Billiet ODWS
What level of complexity is
necessary for life?
C17th microscopists discovered tissues
were made of cells (Hooke 1665 and
Leeuwenhoek 1677)
 C18th and C19th showed that tissues
were made of cells and that the cells of a
particular tissue had a common structure
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© 2007 Paul Billiet ODWS
What level of complexity is
necessary for life?
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Xavier Bichat (17711802): An organ is
composed of different
tissues and several
organs can be grouped
together as an organ
system (e.g. the
digestive system)
An idea of hierarchy of
structure developed:
© 2007 Paul Billiet ODWS
Organism
Organ-system
Organ
Tissue
Cell
What level of complexity is necessary for
life?
Purkinje (1835) Observed a fertilised hen's
egg (a single cell) could develop into an
embryo (many specialised cells in a
compact mass)
 C19th botanists showed that plant tissues
consist of many different types of cells
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© 2007 Paul Billiet ODWS
WHAT IS CELL THEORY
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Matthias Schleiden (1838) & Theodor Schwann (1839)
1.“The cell is the basic unit of living tissue”
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The cell is an autonomous unit (“a citizen”) grouped
together to form an organism (“the society”)
Rudolf Virchow (1858) noted that:
2.“all cells come from pre-existing cells”
© 2007 Paul Billiet ODWS
Organism Theory is the counter argument
Reichert a morphologist: Argued that an..
organism has a structured plan
 Strasberger a cytologist: Cells are connected in an
organism sometimes by
 cytoplasmic bridges so the cytoplasm of one cell
joins to another so the tissue is not made of simple
cells (e.g.plant cell plasmodesmata, fungal hyphae,
striated muscle)
 Some structures are extra cellular found outside cells
e.g. bone or cartilage matrix.
© 2007 Paul Billiet ODWS
Skeletal Muscle
Bone
Cytoplasmic bridges
Cell theory or organismal theory?
That the cell is the basic unit of living
organisms is accepted
 That unicellular organisms carry out all the
functions of life is accepted
 BUT multicellular organisms are not simply
a mass of similar building blocks
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© 2007 Paul Billiet ODWS
More is different!
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As a multicellular organism grows and develops
it follows a structured plan
The cells specialise (differentiate)
The whole organism shows homeostatic
control
A developing multicellular organism shows
emergent properties
It is not just a the sum of the parts
© 2007 Paul Billiet ODWS
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Read your text and briefly in your own
words, summarize what cell theory states
and any examples that counter cell theory