ch.1 the cell (theory)
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THE CELL THEORY
What level of complexity is necessary for life? Aristotle (384 – 322BC)
Matter
Organised material (living)
Unorganised material (non-living)
Heterogeneous (organs)
Homogeneous (tissues)
© 2010 Paul Billiet ODWS
Tissues and Organs
Image Credit Muscle tissue (surloin steak)
Image Credit Kidney longitudinal section
What level of complexity is necessary for life?
C17th microscopists discovered tissues were made of cells (Hooke 1665 and Leeuwenhoek 1677)
Image Credit Cork cells© 2010 Paul Billiet ODWS
Cells
C18th and C19th showed that tissues were made of cells The cells of a particular tissue had a common structure. Image Credit Liver cells
What is a cell?
Taken to its simplest form A plasma membrane… Surrounding cytoplasm… Containing hereditary material.
© 2010 Paul Billiet ODWS
What level of complexity is necessary for life? Xavier Bichat (1771-
1802): An organ is composed of different tissues
Several organs can be grouped together as an organ system (e.g. the digestive system)
An idea of hierarchy of structure developed:
Organism
Organ-system
Organ
Tissue
Cell
© 2010 Paul Billiet ODWS
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.
© 2010 Paul Billiet ODWS
THE CELL THEORY
Matthias Schleiden (1838) & Theodor Schwann (1839) “The cell is the basic unit of living tissue”
The cell is an autonomous unit (“a citizen”) grouped together to form an organism (“the society”).
© 2010 Paul Billiet ODWS
« Omnis cellula e cellula »
Rudolf Virchow (1858) noted that: “all cells come from pre-existing cells”
Image Credit Cell division
THE ORGANISMAL THEORY
The counter arguments:
Reichert a morphologist: Argued that an organism has a structured plan
Image Credit Frog embryo Image Credit Frog embryo fate map
Plasmodesmata
Strasberger a cytologist: Cells are connected in an organism sometimes by cytoplasmic bridges
Image Credit Black sapote (Diospyros) fruit
Acellular organismsSome organisms do not have cellular compartments
Image Credit Common field mushroom (Agaricus bisporus)
Image Credit Fungal hyphae
Homeostasis
Sherrington and Pavlov neurophysiologists: Cells communicate with one another and they are co-ordinated in their actions
Image Credit Spiney dendrites of the hippocampus region of the brain. Red dots show the spines associated with synapses.
Unicellular organisms Some organisms only consist of a single
cell But these do usually have the components
of cells (nucleus, membrane etc)
Image Credit Paramecium
Cellular components
Some cells lack the basic components But as a result their functions are affected.
Image Credit Red blood cells
Tissue culture Cells can be cultured away from a body But this often requires elaborate support
systems
Image Credit Tissue culture hood U of Wisconsin
SUMMARY
2. Certain cells lack the basic componentsCells in multicellular organisms are highly specialisedUnicellular organisms have a cytoplasm that is not subdivided Should be considered as acellular
2. The basic components of the cell are repeated in every cell
1. Some organisms are not divided into cellular compartments = non-cellular
1. Multicellular organisms develop from a single fertilised germ cell (the zygote)
THE ORGANISMAL THEORY
THE CELL THEORY
© 2010 Paul Billiet ODWS
SUMMARY
4. Homeostatic control and co-ordination is required to maintain the whole organism whether it is unicellular or multicellular.
3. Remove cells from complete multicellular organisms requires elaborate life support systems to keep them alive
3. All cells come from cells
Cells can be taken from organisms and cultured away from the body
New individuals can be cultured from isolated cells Regeneration capacity = totipotence
THE ORGANISMAL THEORY
THE CELL THEORY
© 2010 Paul Billiet ODWS
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
© 2010 Paul Billiet ODWS
More is different! 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 the sum of the parts
© 2010 Paul Billiet ODWS