1. THE CELL THEORY
© 2016 Paul Billiet ODWS

2. What level of complexity is necessary for life?
Aristotle (384 – 322BC)
Organised material (living)
Unorganised material (non-living)
Heterogeneous (organs)
Homogeneous (tissues)
Matter
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3. Tissues and Organs Muscle tissue (surloin steak)
Kidney longitudinal section
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4. What level of complexity is necessary for life?
C17th microscopists discovered tissues were made of cells (Hooke 1665 and Leeuwenhoek 1677)
Cork cells
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5. Cells
C18th and C19th showed that tissues were made of cells. The cells of a particular tissue have a common structure.
Liver cells
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6. What is a cell?
Taken to its simplest form A plasma membrane… surrounding cytoplasm… containing hereditary material.
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7. Unicellular organisms
Some organisms only consist of a single cell yet carry out all life functions
But these do usually have the components of cells (nucleus, membrane etc)
Paramecium
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8. What are life functions?
Nutrition
Metabolism
Growth
Response
Excretion
Homeostasis
Reproduction.
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9. Multicellular organisms
Development of a chick embryo
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10. What level of complexity is necessary for life?
Xavier Bichat ( ): 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 into:
Organism
Organ-system
Organ
Tissue
Cell
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11. 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
So all living organisms seem to be composed of cells
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12. 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”).
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13. « Omnis cellula e cellula »
Cell division
Remak & Virchow (1858) noted that: “all cells come from pre-existing cells”
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14. Is the cell really that autonomous?
Cells in multicellular organisms
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15. Cellular components Some cells lack the basic components
But as a result their functions are affected.
Red blood cells
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16. Plasmodesmata
Strasberger observed: Cells are connected in an organism sometimes by cytoplasmic bridges. Not all cells seem to be completely contained in a plasma membrane.
Black sapote (Diospyros) fruit
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17. Acellular organisms Some organisms do not have cellular compartments
Common field mushroom (Agaricus bisporus)
Fungal hyphae
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18. Giant algal cells Acetabularia © 2016 Paul Billiet ODWS
Acetabularia
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19. Acellular tissues: Striated muscle fibres
Striated muscle viewed at x400
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20. Homeostasis
Spiney dendrites of the hippocampus region of the brain. Red dots show the spines associated with synapses.
Sherrington and Pavlov neurophysiologists: Cells communicate with one another They are co-ordinated in their actions
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21. Tissue culture Cells can be cultured away from a body
But this often requires elaborate support systems
Tissue culture hood U of Wisconsin
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22. THE ORGANISMAL THEORY
The counter arguments: Reichert a morphologist: Argued that a multicellular organism has a structured plan
Frog embryo
Frog embryo fate map
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23. SUMMARY THE ORGANISMAL THEORY THE CELL THEORY
1. Multicellular organisms develop from a single fertilised germ cell (the zygote)
1. Some organisms are not divided into cellular compartments
= non-cellular
2. The basic components of the cell are repeated in every cell
Where they are absent or in multiples this affects life processes
e.g. anucleate red blood cells cannot reproduce
e.g. muscles cells contain many nuclei but form from many cells that fuse
2. Certain cells lack the basic components e.g. red blood cells
Cells in multicellular organisms are highly specialised
Unicellular organisms have a cytoplasm that is not subdivided Should they be considered as acellular?
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24. SUMMARY THE ORGANISMAL THEORY THE CELL THEORY
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
3. Remove cells from complete multicellular organisms requires elaborate life support systems to keep them alive
4. Homeostatic control and co-ordination is required to maintain the whole organism whether it is unicellular or multicellular.
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25. 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 independent building blocks.
© 2016 Paul Billiet ODWS

26. 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.
© 2016 Paul Billiet ODWS