Organisms reproduce like offspring. There are two types of reproduction: ASEXUAL REPRODUCTION - producing offspring from only 1 parent offspring look EXACTLY like parent this type of reproduction is best suited for a stable environment occurs in unicellular organisms and some plants SEXUAL REPRODUCTION - producing offspring from two parents offspring have characteristics from BOTH parents this type of reproduction is suited for either a stable environment OR a changing environment

Cells are organisms. They must reproduce. Cells need to divide (reproduce) for... -growth -healing and repair -to replace dead or damaged cells New cells formed must be IDENTICAL to original cells WHY ? So the new cells can perform the same function as the original cell !

MITOSIS - the process cells use to make exact copies of the cell (aka - Nuclear Reproduction) Mitosis is a process that makes sure each cell gets the same DNA ! Mitosis occurs in SOMATIC CELLS (body cells) ex) liver cells, skin cells, lung cells Somatic cells are DIPLOID (having the total number of chromosomes) Human diploid number = 46 Mitosis begins w/ ONE diploid somatic cell Mitosis ends w/ TWO diploid somatic cells that are identical ! In order for the cells made by mitosis to be identical, they must have the same DNA ! It is important that the cells made during Mitosis are identical so that the new cells made will do the same functions as the original cell !

The Cell Cycle The cell cycle is the series of events a cell goes through during its lifetime It includes 3 main parts : Interphase (G1, S phase, and G2), Mitosis, and Cytokinesis. The following is a description of the events that occur during the cell cycle.

Interphase (not actually part of Mitosis, but included in the Cell Cycle) G1 - Cell is doing what cell normally does (performing cell functions) S phase - DNA Replication occurs G2 - Cell prepares to divide (organelles are doubled in numbers)

Prophase Chromatin condenses into chromosomes Nuclear membrane disappears Centrioles begin to move to opposite ends of cell (aster begins to form) The centromere is a belt-like structure that holds sister chromatids together. Sister chromatids are exact copies of a chromosome. Sister chromatids centromere

Metaphase Sister chromatids line up along center (middle) of cell Spindle fibers attach to each centromere

Anaphase Spindle fibers shorten Each centromere breaks apart One member of each sister chromatid pair is pulled toward each end of the cell

Telophase Nuclear membranes form around each set of chromosomes Chromosomes uncoil into chromatin The cell now has 2 nuclei and is ready to divide

Cytokinesis The cell divides to form two identical cells Occurs after telophase CYTOKINESIS - the actual, physical division of one cell into two cells Cytokinesis is different in plants and animals (due to plants having a cell wall)