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THE CELL THE CELL THEORYTHEORY

© 2016 Paul Billiet ODWS

http://www.saburchill.com/IBbiology/bio_hp.html

What level of complexity is What level of complexity is necessary for life?necessary for life?

• Aristotle (384 – 322BC)

MatterOrganised

material (living)

Unorganised material (non-living)

Heterogeneous (organs)

Homogeneous (tissues)



Tissues and OrgansTissues and Organs

Muscle tissue (surloin steak) Kidney longitudinal section


http://www.beefretail.org/cmimages/beefretail/recipeimages/1422TopSirloinSteak01.jpg



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C17th microscopists discovered tissues were made of cells (Hooke 1665 and Leeuwenhoek 1677)

Cork cells© 2016 Paul Billiet ODWS

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CellsCellsC18th 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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What is a cell?What is a cell?• Taken to its simplest form

A plasma membrane…surrounding cytoplasm…containing hereditary material.



Unicellular Unicellular organismsorganisms

• 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© 2016 Paul Billiet ODWS

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What are life functions? Nutrition Metabolism Growth Response Excretion Homeostasis Reproduction.



Multicellular Multicellular organismsorganisms

Development of a chick embryo© 2016 Paul Billiet ODWS

http://www.microscopy-uk.org.uk/mag/artnov04macro/mlchicken.html







• 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 into:

Organism

Organ-system

Organ

Tissue

Cell




• 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



THE CELL THEORYTHE 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”).



«« Omnis cellula e cellula Omnis cellula e cellula » »Remak & Virchow (1858) noted that: “all cells come from pre-existing cells”

Cell division© 2016 Paul Billiet ODWS

http://www.sciencecentric.com/news/07091003-mystery-behind-how-nuclear-membrane-forms-during-mitosis-solved.html

http://www.sciencecentric.com/news/07091003-mystery-behind-how-nuclear-membrane-forms-during-mitosis-solved.html


Is the cell really that Is the cell really that autonomous?autonomous?

• Cells in multicellular organisms



Cellular componentsCellular components• Some cells lack the basic components• But as a result their functions are affected.

Red blood cells© 2016 Paul Billiet ODWS

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PlasmodesmataPlasmodesmataStrasberger 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© 2016 Paul Billiet ODWS

http://www.doctortee.com/dsu/tiftickjian/cse-img/botany/plant-anat/fruit-seed/diospyros-endosperm.jpg




Acellular organismsAcellular organismsSome organisms do not have cellular compartments

Common field mushroom (Agaricus bisporus)

Fungal hyphae © 2016 Paul Billiet ODWS

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Giant algal cells

http://www.coexploration.org/bbsr/coral/assets/images/acetabularia.jpgAcetabularia © 2016 Paul Billiet ODWS

Acellular tissues: Striated muscle fibres

Striated muscle viewed at x400© 2016 Paul Billiet ODWS

http://images.google.com/images?q=LS+sketetal+muscle&gbv=2&ndsp=18&hl=en&start=54&sa=N

HomeostasisHomeostasisSherrington and Pavlov neurophysiologists: Cells communicate with one anotherThey are co-ordinated in their actions

Spiney dendrites of the hippocampus region of the brain. Red dots show the spines associated with synapses.


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Tissue cultureTissue culture• Cells can be cultured away from a body• But this often requires elaborate support

systems

Tissue culture hood U of Wisconsin© 2016 Paul Billiet ODWS

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THE ORGANISMAL THE ORGANISMAL THEORYTHEORY

The counter arguments:Reichert a morphologist: Argued that a multicellular organism has a structured plan

Frog embryo Frog embryo fate map© 2016 Paul Billiet ODWS

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SUMMARYSUMMARY

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?

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 reproducee.g. muscles cells contain many nuclei but form from many cells that fuse

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


SUMMARYSUMMARY

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

THE ORGANISMAL THEORY

THE CELL THEORY


Cell theory or Cell theory or organismal theory?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.


More is different!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.


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