CELL DIVISION BIG IDEA organisms grow reproduce maintain

CELL DIVISION • BIG IDEA: organisms grow, reproduce, & maintain themselves through cell division. • Cell division occurs in all organisms • Cell division is part of the cell cycle. • Both sexual & asexsual reproduction involve cell division

CELL DIVISION OCCURS IN ALL ORGANISMS • CELL DIVISION IS INVOLVED IN MANY FUNCTIONS – Occurs in all organisms; unicellular organisms reproduce through this; in multicellular, cell division allows for growth, development, repair and aids in reproduction. • GENETIC MATERIAL OF EUKARYOTIC CELLS IS ORGANIZED IN CHROMOSOMES – When a cell divides, each new (daughter) cell gets a full set of genetic material (DNA). • CELL DIVISION IS INVOLVED IN GROWTH, DEVELOPMENT & REPAIR

Genetic Material of Eukaryotes Organized into Chromosomes • When a cell divides, each new cell needs a complete set of genetic material • This is DNA (deoxyribonucleic acid); contains data for cell’s growth & functions. • Made of 2 strands of material twisted together into a double helix (shown by Watson & Crick) • Most of DNA is in nucleus as a mass of loose strands called chromatin • Before a cell divides, DNA gets copied, then starts to tightly wrap around proteins to make CHROMOSOMES (2 identical chromatids held together by centromere) • All human body cells have 46 chromosomes, fruit flies have 8 and corn plants have 20.

CELL DIVISION USED TO GROW, DEVELOP & REPAIR • We all started as 1 cell 26 billion when born 100 trillion as adult • In multicellular organisms, cell division is needed for growth, development, and repair. • As an organism grows & increases its number of cells, many become specialized to do specific jobs. • When an organism is injured or aged, its worn out cells get replaced by new healthy cells via cell division. (your throat cells only last about 23 days).

Growth & Development • Larger organisms just have more cells (not larger). Cell size is limited by its surface area to volume ratio. (When it gets too big, it divides into 2 smaller cells to function betterstill not sure why). • During development, cells become specialized to do certain jobs. • These cells may take on shapes or structures to help them do their jobs (long, thin nerve cells or layered skin cells). They still have the same DNA as other cells in the body.

REPAIR • Body repairs injuries by cell division. • When skin is cut, skin cells on either side of cut make new cells to heal the wound. • As cells age & die, they need to be replaced. Human body is made of about 200 different types of cellswhich are replaced at different rates. Skin cells wear out quickly, so replaced quickly (about 40, 000 every minute). Brain cells live a long time (many years) and don’t divide very often.