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Cell Theory A well-substantiated explanation of some aspect of the natural world that is repeatedly confirmed through observation and experimentation. Hooke first described cells in 1665 after examining cork and other plants with a microscope, He saw a TREND…. Which means, “To have a general tendency” LIVING ORGANISMS ARE MADE OF CELLS 1.1.A1 Which allows for discrepancies and/or exceptions to exist Exception Example Caveat The presence of extracellular material in an organism contradicts the idea that the organism is made up of cells only Very large cells with ONE nucleus Vitreous humor of the eye, mineral deposits in bone, cellulose in plant cell walls These materials were produced by cells! Very large cells with many nuclei Muscle cells called fibres are very long (≈30mm) and multinucleate Giant algae like Acetabularia are up to ≈ 100 mm with a single nucleus Giant algae like caulerpa are among the biggest single cells in the world (up to ≈ 1m) Fungal hyphae with a continuous cytoplasm and tubular cell wall They are surrounded by a single cell membrane and are formed by division of preexisting cells.