CHAPTER 9

The Cell Cycle  The cell cycle is the series of events that cells go through as they grow and divide.

9-1 Cell Growth  Two reasons why cells divide instead of continuing to grow; 1. The larger a cell becomes the more demands the cell places on its DNA. 2. The cell has more trouble moving nutrients and waste across the cell membrane.

DNA “overload”  When a cell is small, the information stored in the DNA is able to meet all of the cells needs.  As a cell increases in size, it usually does not make extra copies of DNA.  If a cell were to grow without limits an “information crisis” would occur.  Example: small town library with more and more people

Exchanging Material  The rate at which the exchange of food, O2, H2O enter the cell and waste leaves the cell through the cell membrane depends on the surface area.  The rate at which food and O2 are used up and the waste products are produced depends on the cell’s volume.  This is the reason why a cell must divide.

Ratio of Surface Area (SA) to Volume.  SA= 1cm x 1cm x 6(faces) = 6cm ² (squared)  Volume = 1cm x 1cm x 1cm = 1 cm³ (cubed)  Ratio 6:1  SA=2cm x 2cm x 6 = 24 cm²  Vol=2cm x 2cm x 2 cm = 8 cm³  Ratio 3:1  As cells become larger, its volume increases faster than its surface area.

Ratio of Surface Area to Volume

Ways cell division solves problem of cell growth  Cell division provides each daughter cell with its own copy of DNA.  Cell division increases the surface area of the original cell.  Cell division reduces the original cell’s volume.