1. THE CELL THEORY Topic 2.1
Adapted by Laura Sugden from the works of Paul Billiet (ODWS) and Stephen Taylor (iBiology)

2. Principles of Cell Theory
All living things are made of cells.
Cells are the smallest units of life.
Cells come only from other cells.

3. Scientific Method
Cell theory is a great example of the scientific process .
Many scientists were involved in our understanding of the modern day cell theory.
Hooke
Van Leeuwenhoek
Pasteur
Remak
To name a few!

4. Robert Hooke ( )
Coined the therm cells by looking at cork sections under a microscope.
Image Credit Cork cells
© 2010 Paul Billiet ODWS

5. Antonie van Leewenhoek (1632-1723)
Master lens-maker that discovered “animalcules” in lake water.
He is credited as the father of microbiology and the discoverer of cells.

6. Spontaneous Generation? Nope!
Louis Pasteur 1874
Germ Theory
Pasteurization
Vaccines
Robert Remak 1858
Discovered Cell Division
Ideas plagarized by Rudolf Virchow

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

8. Cells carry out life functions:
Metabolism
Response to the environment
Growth
Reproduction
Nutrition
Homeostasis

9. Single celled organisms
Limitations….
Single celled organisms
Muscle cells and fungal hyphae are very long and multinucleated.
Viruses…living or not?

10. Cells Tissues are made of cells
Image Credit Liver cells
Tissues are made of cells
The cells of a particular tissue have a common structure.

11. 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:
Organism
Organ-system
Organ
Tissue
Cell
© 2010 Paul Billiet ODWS

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”).
Cells arise from other cells, each cell is independent from the other, but working together for the organism as a whole.
© 2010 Paul Billiet ODWS

13. THE ORGANISMAL THEORY The counter arguments:
Morphologists argued that an organism has a structured plan and that the original cell just expands into the whole organism.
In the following slides I will show some of the evidence this counter theory is based on.
Image Credit Frog embryo fate map
Image Credit Frog embryo

14. Plasmodesmata
Cells are connected in an organism sometimes by cytoplasmic bridges
Image Credit Black sapote (Diospyros) fruit

15. Homeostasis
Image Credit Spiney dendrites of the hippocampus region of the brain. Red dots show the spines associated with synapses.
Cells communicate with one another and they are co-ordinated in their actions

16. 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

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 Wisconsin

18. 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

19. More is different!
As a multicellular organism grows and develops it follows a structured plan
The cells specialize (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

21. SI Review

27. Homework 2.1
SHOW YOUR WORK! You will need to print this slide on a 8.5 X 11 sheet.

30. Find the Actual SIZE

31. Find the Magnification of these images

34. Volume Volume determines the amount metabolism in the cytoplasm
Metabolism will require import of precursors
Metabolism will result in the export of secretions
And the export of excretory products
© 2010 Paul Billiet ODWS

35. Surface area
Surface area will determine the exchange of materials between the cell and its environment
Bigger cells will metabolise more
But they will need more surface to support that metabolism
And the sites of metabolism in bigger cells will be further from the surface of the cell
© 2010 Paul Billiet ODWS

36. (6 x 12)
(6 x 32)
Surface Area of a Cube = 6 x Length2

37. Comparing Surface Area and Volume changes
© 2010 Paul Billiet ODWS

38. Surface Area:Volume Ratio
© 2010 Paul Billiet ODWS

40. Solving the problem
Bigger cells have a greater metabolism than smaller cells
BUT bigger cells have a proportionally less surface for exchange
How to increase surface area with increasing size?
© 2010 Paul Billiet ODWS

42. Throw out extensions Microvilli of small intestine epithelium
Image Credit

43. Flatten into a thin film
Image Credits

44. Divide the cytoplasm into smaller volumes
8-cell Embryo
Early human embryos
Zygote
Image Credit
Image Credit

45. Multicellular organisms show the same adaptations
Flowering plants have an extensive, branched rooting system to absorb water and minerals
Image Credit

46. Multicellular organisms show the same adaptations
Mammals have a long small intestine with internal folding to absorb digested food
Image Credit C. Candalh, INSERM