 The larger a cell becomes, the more demands it places on its DNA & the less efficient it is at moving nutrients/wastes  Enough DNA = abundant cell instructions  Ratio of surface area to volume must remain relatively high to meet cell demands › High surface = more exchange › Low volume = less nutrients/wastes

 Defined as process by which a cell divides into two new daughter cells › Results in each daughter cell receiving one complete copy of genetic info  Sexual reproduction – offspring produced by the fusion of two gametes from each of two parents › Offspring inherit genes/traits from each parent  Asexual reproduction – offspring produced by division of one parent’s cell › Very quick, and offspring is genetically identical to parent (ex. bacteria, hydra) › Lacks genetic diversity

 Defined as bundled “packages” of DNA containing genetic information  Prokaryotes typically have only one chromosome the is circular and located in the cytoplasm  Eukaryotes contain multiple chromosomes contained within a nucleus › Wrapped around histones (proteins) to create chromatin  Chromosomes make it possible to separate DNA precisely during division

Eukaryotic chromosome Prokaryotic chromosome

 Binary fission – Prokaryotic form of asexual reproduction  Results in two genetically identical organisms  Four phases – Eukaryotic cycle › Interphase  G 1 – cell growth  S – DNA replication  G 2 – prep for mitosis › Cell division  M – consists of mitosis &  cytokinesis

 Prophase – chromatin condensed & duplicated chromosomes become visible; spindles form  Metaphase – centromeres/sister chromatids line up across center of cell; spindle fibers attach  Anaphase – sister chromatids separate and move toward opposite ends of cell  Telephase – chromosomes spread out back into chromatin tangle at opposite ends of cell; nuclear envelope re-forms  Cytokinesis – Cell splits into two › Animal  membrane pinches inward › Plant  cell plate forms  Mitosis Animation and “real” mitosis Mitosis Animation“real” mitosis

 Regulatory proteins inside & outside of the cell control cell cycle › Cyclins – family of proteins that control the timing of the eukaryotic cell cycle › Internal – monitors mitosis, etc., › External – adjusts speed of cell cycle, especially embryonic development and wound healing › Growth factors stimulate growth & division  Cells often stop dividing when they come in contact with other cells

 Apoptosis – programmed cell death  Cancer – uncontrolled cell growth due to cells not responding to signals the regulate growth (disease of cell cycle) › Causes – defects in genes often as a result of tobacco use, radiation exposure, infections › Treatment – surgical removal, chemotherapy, radiation

 Defined as the process by which cells become specialized into many different types  Many cells differentiate at the embryonic stage, but some do during adulthood  Stem cells are important

 Defined as unspecialized cells from which differentiated cells develop › Totipotent – can develop into anything (ex. egg and sperm cells) › Pluripotent – can develop into most, but not all, cell types (Embryonic stem cells) › Multipotent – can develop into many cell types (Adult stem cells)  Replace cells like nerve, blood, skin

 Offers the potential benefit of using undifferentiated cells to repair or replace damaged cells and tissues  Ethical issues, especially surrounding “harvesting”, make this a controversial topic in society