1. THE CELL THEORY

2. 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 ODWSODWS

3. Tissues and Organs Image Credit Muscle tissue (surloin steak)Muscle tissue (surloin steak) Image Credit Kidney longitudinal sectionKidney longitudinal section

4. What level of complexity is necessary for life? C17th microscopists discovered tissues were made of cells (Hooke 1665 and Leeuwenhoek 1677) Image Credit Cork cellsCork cells © 2010 Paul Billiet ODWSODWS

5. Cells C18th and C19th showed that tissues were made of cells The cells of a particular tissue had a common structure. Image Credit Liver cellsLiver cells

6. What is a cell? Taken to its simplest form A plasma membrane… Surrounding cytoplasm… Containing hereditary material. © 2010 Paul Billiet ODWSODWS

7. 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 ODWSODWS

8. 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 ODWSODWS

9. 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 ODWSODWS

10. « Omnis cellula e cellula » Rudolf Virchow (1858) noted that: “all cells come from pre-existing cells” Image Credit Cell divisionCell division

11. THE ORGANISMAL THEORY The counter arguments: Reichert a morphologist: Argued that an organism has a structured plan Image Credit Frog embryoFrog embryo Image Credit Frog embryo fate mapFrog embryo fate map

12. Plasmodesmata Strasberger a cytologist: Cells are connected in an organism sometimes by cytoplasmic bridges Image Credit Black sapote (Diospyros) fruitBlack sapote (Diospyros) fruit

13. Acellular organisms Some organisms do not have cellular compartments Image Credit Common field mushroom (Agaricus bisporus)Common field mushroom (Agaricus bisporus) Image Credit Fungal hyphaeFungal hyphae

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

15. Unicellular organisms Some organisms only consist of a single cell But these do usually have the components of cells (nucleus, membrane etc) Image Credit ParameciumParamecium

16. Cellular components Some cells lack the basic components But as a result their functions are affected. Image Credit Red blood cellsRed blood cells

17. Tissue culture Cells can be cultured away from a body But this often requires elaborate support systems Image Credit Tissue culture hood U of WisconsinTissue culture hood U of Wisconsin

18. SUMMARY 2. Certain cells lack the basic components Cells in multicellular organisms are highly specialised Unicellular 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 ODWSODWS

19. 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 ODWSODWS

20. 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 ODWSODWS

21. 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 ODWSODWS