Science 9 HORMONES FOR CELL GROWTH AND DIVISION

 Cell growth and cell division are important for understanding differences between organisms of the same species  Cells communicate with one another using chemical messengers  These messengers are called hormones  Hormones are produced in cells in one part of the body and can affect cell division and growth in another part of the body  Some hormones trigger cells to grow and divide DIFFERENCES FROM ONE ORGANISM TO ANOTHER

 Plants produce a variety of growth hormones  Auxins are plant hormones that cause cells to grow longer  Cytokinins are plant hormones that stimulate cell division  They are found in the roots but communicate with all parts of the plant PLANT GROWTH HORMONES

 Growth hormone (GH) is produced in the pituitary gland of humans  It is carried by blood to all areas of the body  It does not affect all parts of the body in the same way  Low amounts of GH during childhood can cause dwarfism and high amount can cause gigantism ANIMAL GROWTH HORMONES

 Humans grow fastest during the nine months before birth and the first three months after  Not all body parts grow at the same rate CELL DIVISION AND PATTERNS OF GROWTH

 Very few of the cells you were born with are still dividing  Red blood cells live about 120 days  Skin cells are replaced daily  To stay alive, we rely on cell division  There is a limit to how often a cell can divide  Eventually, cells die and are not replaced  Injuries are not repaired  Accumulating damage and the function of organs are compromised AGING AND CELL DIVISION