The Cell Theory WHAT ARE CELLS AND WHERE DID THEY COME FROM? What is a Cell? Use the pictures below and follow the procedure on pg. 168 Plant Cells Nerve Cell Bacteria cells Paramecium Think About It 1. Use your observations to write your own definition of a cell (may use background knowledge) Example: A cell is a structure within a living thing that has a definite boundary enclosing the material inside 2. Classify the cells that you observed into two or more groups. Explain what characteristics you used to put each cell in a particular group. Possible answers: Plant cells vs. other cells, cells with a nucleus vs. cells without a nucleus The Cell Theory Erythrocytes: Red Blood Cells (RBC) carry O 2 and CO 2 Some Random Cell Facts The average human being is composed of around 100 Trillion individual cells There are about 200 different cell types in the human body There are more bacterial cells in a human body than human cells (19:1) Cells will self destruct if damaged or infected (called apoptosis) Visualizing Cells Light Microscope Can observe living cells Magnification Eyepiece (10x) Objective lens (DIN) Red= DIN 4 = 4x Yellow= DIN 10 = 10x Blue= DIN 40 = 40x Magnification = Eyepiece X Objective low power 4x * 10x = 40x medium power 10x * 10x = 100x high power 40x * 10x = 400x Electron Microscopes Can magnify much higher than light microscopes Very expensive Big and non-portable 2 types S.E.M. (scanning) T.E.M. (transmission) Scanning Electron Microscope (S.E.M.) Shows an image of the scanned surface Useful for looking at 3-D structure of specimens Butterfly Eye S.E.M. 22,000X Transmission Electron Microscope (T.E.M.) Shows a cross section view of specimens Useful for viewing the insides Plant Leaf T.E.M. 42,000x Discovery of Cells English Scientist, Robert Hooke, discovered cells while looking at a thin slice of cork. He described the cells as tiny boxes or a honeycomb He thought that cells only existed in plants and fungi Anton van Leuwenhoek Used a handmade microscope to observe pond scum & discovered single- celled organisms microscope He called them wee beasties He also observed blood cells from fish, birds, frogs, dogs, and humans Therefore, it was known that cells are found in animals as well as plants Year Gap??? Between the Hooke/Leuwenhoek discoveries and the mid 19 th century, very little cell advancements were made. This is probably due to the widely accepted, traditional belief in Spontaneous Generation. Spontaneous Generation For much of history, people believed that animals could come from non-living sources. Historical documents contain recipes for creating creatures such as: bees, frogs, mice, etc. These recipes were based on observations. When the Nile river flooded, soon many frogs appeared in the mud. If damp rags were left in a pile of wheat grain, many mice appeared 21 days later. Jar-1 Left open: Maggots developed Flies were observed laying eggs on the meat in the open jar Jar-2 Covered with netting: Maggots appeared on the netting Flies were observed laying eggs on the netting Jar-3 Sealed: No maggots developed Francisco Redi Lazzaro Spallanzani (1767) Set up an experiment to test whether a vital force in the air could give rise to microorganisms. Spallanzanis hypothesis: Beef broth becomes cloudy due to bacteria present in the air. The bacteria from the air enter the broth and contaminate it, rather than the bacteria arising from the air or broth itself. Spallanzanis Experiment The Big Prize The Paris Academy of Science offered a prize to the person who could best resolve the spontaneous generation debate once and for all. And the winner was Louis Pasteur (1864): A scientist who designed an experiment using a flask that would allow air containing the vital force to enter the flask, but would keep microorganisms out. Louis Pasteur Broth Experiment Development of Cell Theory German Botanist, Matthias Schleiden, concluded that all plant parts are made of cells German physiologist, Theodor Schwann, who was a close friend of Schleiden, stated that all animal tissues are composed of cells. Development of Cell Theory Rudolf Virchow, German physician, after extensive study of cellular pathology, concluded that cells must arise from preexisting cells. The Cell Theory Complete The 3 Basic Components of The Cell Theory were now complete: 1. All organisms are composed of one or more cells. (Schleiden & Schwann)( ) 2. The cell is the basic unit of life in all living things. (Schleiden & Schwann)( ) 3. All cells are produced by the division of preexisting cells. (Virchow)(1858) ProkaryotesEukaryotes No Nucleus: DNA (the genetic material) floats around in cytoplasm (forms a nucleoid) Yes Nucleus: Membrane bound organelle that contains DNA (the genetic material) No membrane-bound organelles Yes membrane-bound organelles Much smaller in sizeGenerally larger in size Very simple structureMore complex structure Prokaryotes vs. Eukaryotes