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

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

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!

Robert Hooke (1635-1703) Coined the therm cells by looking at cork sections under a microscope. Image Credit Cork cells © 2010 Paul Billiet ODWS

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.

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

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

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

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

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.

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

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

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

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

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

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

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

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 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

SI Review

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

Find the Actual SIZE

Find the Magnification of these images

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

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

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

Comparing Surface Area and Volume changes © 2010 Paul Billiet ODWS

Surface Area:Volume Ratio © 2010 Paul Billiet ODWS

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

Throw out extensions Microvilli of small intestine epithelium Image Credit www.cytochemistry.net/

Flatten into a thin film Image Credits http://anatomia.uw.hu/

Divide the cytoplasm into smaller volumes 8-cell Embryo Early human embryos Zygote Image Credit http://www.advancedfertility.com/ Image Credit http://www.rmfcfertility.com/

Multicellular organisms show the same adaptations Flowering plants have an extensive, branched rooting system to absorb water and minerals Image Credit http://ecomerge.blogspot.com

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