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The Cell Theory Microscopes Provide the Windows to the World of the Cell The Men • Anton Van Leeuwenhoek (1600’s) • Credit for the first microscope • Looked at pond water and saw “wee beasties” Robert Hooke • Observed plant stems, wood, and cork (1600’s) • Saw all the tiny chambers and called them CELLS • What cell part did Hooke observe? • Cell Wall Robert Brown (1833) • Observed that cells had a dark structure within plant cells • Brown observed the nucleus Matthias Schleiden (1838) • Stated that all plants are made of Cells • Made many observations of plants around the area Theodor Schwann (1839) • Stated that all animals are made of Cells • Observed many animal tissues Rudolf Virchow (1855) • Stated that all cells come from pre-existing cells • Cells arise from the division of pre-existing cells The Cell Theory • All living things are composed of cells • Cells are the basic unit of structure and function in living things • All cells come from pre-existing cells Exceptions to the Cell Theory • Viruses – are not cellular • Mitochondria and chloroplast – each contain genetic material and can reproduce Endosymbiotic Theory • What is this? • Concerns the origins of mitochondria and plastids (chloroplasts) from prokaryotic cells • Endosymbiont • Cell that lives within another cell Endosymbiotic Theory • Endosymbionts gained entry to cell as undigested prey items or parasites and began a mutually beneficial relationship • Occurred by endocytosis (cell parts are engulfed) • Over time this would turn into a single organism whose parts are inseparable Endosymbiotic Theory Evidence • Mitochondria & Plastids • Have enzymes and transport systems that are the same as in plasma membrane of prokaryotes • Also replicate by same process as certain prokaryotes Endosymbiotic Theory Evidence Cont’d • Both organelles have DNA, have mechanisms to transcribe /translate proteins • Size, Nucleotide Sequence, & Sensitivity to antibiotics are similar to prokaryotes