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CHAPTER 4: WHY ARE ALL ORGANISMS MADE OF CELLS? Very Little Animalcules ~300 years ago – Leeuenhoek & Hooke found out about cells 4.1 WHY ARE ALL ORGANISMS MADE OF CELLS? protoplasm – “juices” found in cells by Hooke; term later discarded ALL ORGANISMS ARE MADE OF CELLS Schleiden, Schwann – scientists that argued all cells are alive Virchow – scientist who said omnis cellula e cellula – “all cells from cells” 1) cells never arise from noncellular material 2) diseases result from changes in specific kinds of cells cell theory – summarized from work of Schleiden, Schwann, and Virchow 1) all organisms are composed of one or more cells 2) cells, themselves alive, are the basic living unit of organization of all organisms 3) all cells come from other cells EVERY CELL CONSISTS OF A BOUNDARY, A CELL BODY, AND A SET OF GENES All cells have 3 common features: 1) a boundary that separates the inside of the cell from the rest of the world 2) a set of genes 3) a cell body plasma membrane – cell’s boundary – highly organized & responsive structure also regulates internal environment – selective admission & excretion nucleus – in eukaryotes, the DNA is confined in this structure (5-10% of volume of cell) its presence alone distinguishes the eukaryotes from prokaryotes nucleoid – in prokaryotes, the DNA occupies a limited region of cell, the ~ organelles – tiny structures inside protoplasm of eukaryotic cells cytoplasm – part of the cell inside the plasma membrane, but outside the nucleus cytosol – part of cytoplasm not contained within organelles cytoskeleton – network of protein fibers running through cytosol gives cell its shape, holds organelles in place, participates in cell movement HOW ARE CELLS ALIVE? Cells perform chemical reactions, obtain energy from their surroundings, respond to their environments, change over time, reproduce, and share and evolutionary history. Obtain energy – most can oxidize glucose carbon dioxide & water Cells change with time – chemically & mechanically Cell reproduction depends on cell’s ability to read DNA Responds to environmental changes too Cells must deal with garbage, cell remnants from wear & tear Special mechanisms & organelles serve this purpose Different cells – same molecules, same biochemical pathways, and same types of organelles Common evolutionary ancestor WHAT ARE THE ADVANTAGES OF CELLULAR ORGANIZATION? Most eukaryotic cells are about the same size – 10 to 100 micrometers (μm) Some dramatically larger (ostrich egg, meter long plant fibers, giraffe leg muscles) Prokaryotes are usually about .4 to .5 μm
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Cells are usually small because subdivision offers many advantages What problems would you face if you were one very large cell?
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