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CELL THEORY A Brief History Robert Hooke named the cell [1665] based on observations of the cell walls of cork tissue Anton van Leeuwenhoek documented unicellular organisms based on observations of protozoa [1673] and bacteria [1683] Paramecium - Protocista Amoeba - Protocista Matthias Schleiden proposed that cells were the fundamental units of plants based on observations of plant tissue [1838] Plant cells t Cell Theodor Schwann proposed that cells were the fundamental units of animals based on observations of animal tissue [1839] Blood Sperm Schleiden and Schwann are credited as the founders of The Cell Theory [1839] All living things are made of cells. Cells exhibit the fundamental characteristics of life: Obtain energy—photosynthesis, chemosynthesis, or digestion Use energy—respire Excrete Waste Show Order Homeostasis Evolve Reproduce Move Respond to changes in environment Grow and repair damage to self The development of the Cell Theory involved the input of numerous individuals from various nationalities over many years Rudolph Virchow stated “omnis cellula a cellula ” [all cells arise from pre-existing cells based on observations of dividing cells [1855] Rudolph Virchow stated “omnis cellula a cellula ” [all cells arise from pre-existing cells based on observations of dividing cells [1855] The Cell Theory was modified to incorporate Virchow’s work All organisms are made of cells Cells are the smallest structural and functional unit of an organism [that carries out the life processes] All cells come from pre-existing cells And, what about viruses? Are not composed of cells but consist of a nucleic acid (DNA or RNA) in a protein coat Yet conduct all of the cell processes (although with help, not independently) SO: Could there be an organism that does not contain a single cell? Might there be some other fundamental unit of life? At least, in some cases? Are the life processes sufficient criteria to distinguish between the living and the non-living? Microscopes Max magnification – X1000 Max Resolution 0.2um Max magnification X1000,000 Max Resolution 0.5nm Microscopic measurements mm – millimeters μm – micrometer nm - nanometers 1m = 1000mm = 1000,000μm= 1000,000,000nm Comaparison of Light and Electron Microscopes Light Microscope Human Cheek Cell Nerve Cells Transmission Electron Microscope Plant Cell Mitochondrion Scanning Electron Microscope Human Sperm Insect Head Sizes of Biological Structures Thickness of leaf O.5mm Paramecium 200μm Sharp end of pin 100 μm Plant cell 40μm Animal cell 20μm Mitochondrion 1μm Bacterium 0.5-1μm Ribosome 20nm DNA molecule 2nm Hydrogen atom 0.04nm Red and White Blood Cells S.E. M Light Microscope