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Control of the Cell Cycle Division VS Differentiation • Development of Multicellular Organisms - A fertilized __egg__ ( __one__ __cell__ ) gives rise to a large number of __identical__ cells through __cell_ ___division__ - As development continues, cells ___increase__ in __number__ BUT also go through __cell___ ___differrentiation___ Cell Differentiation– when cells become __specialized__ in __structure____ and ___function__ *How various cell types ( _blood, muscle, skin cells_) are organized: __Cells__ ____Tissues___ ___Organs__ ____Organ Systems___ Stem Cells - __unspecialized __ cells that have the ability to ___differentiate__ into one or more types of specialized cells Examples 1.) ___Embryonic Stem Cells____ 2.)____Adult Stem Cells (found in bone marrow)______________ Control of Cell Division– the cell cycle is driven by a ___chemical control system_____ • Internal ( __enzymes__) and external ( ___environment__) signals help to __control___ the cell cycle • ___Checkpoints___ are also in place to ___regulate___ the cell cycle • __Stop_ and __Start__ signals keep the cell “___cycling____” correctly Uncontrolled cell Division– sometimes cells do NOT respond to the body’s control system and ___divide___ __excessively__ Cancer – a single cell is transformed into a __cancer__ __cell__ ( do not obey the control systems) • Normally the bodies __immune__ system will recognize that the cell is damaged and __destroy__ it • But if it ___evades__ destruction, the cancer cell will continue to __divide__and each daughter cell will be cancerous • A mass of cancer cells is called a ___tumor____ Malignant Tumor – mass of cells that __invades__ / ___impairs__ the functions of one or more organs Benign Tumor – mass of abnormal cells that remain at the ____original site___ (do not spread) - “noncancerous”