Chapter 10 Cell Growth and Division

Introduction What happens to the cells when a living thing grows? Do the cells get larger also? Usually, living things grow by producing more cells. Cells divide rather than continuing to grow indefinitely.

Limits to Cell Growth Two main reasons why cells divide instead of continuing to grow: 1. DNA Overload 2. Exchanging Materials

1. DNA Overload The larger a cell becomes, the more demands the cell places on its DNA. Only enough DNA available to support the activities of a small cell If a cell were to grow without limit, an “information crisis” would occur

2. Exchanging Materials If a cell got too large, it would be more difficult to get sufficient amounts of oxygen and nutrients in and waste products out. Why? Surface Area and volume

Exchanging Materials con’t Surface area of the cell determines rate at which the exchange of food, oxygen, and water enter a cell and waste materials leave (all through the cell membrane). Cell’s volume determines the rate at which food and oxygen are used up and waste products are produced. The relationship between a cell’s volume and its surface area is the key.

Ratio of Surface Area to Volume If a cell grows larger, then the volume increases much more rapidly than the surface area, causing the ratio of surface area to volume to decrease. The problem is that the cell would not be able to get enough oxygen and nutrients in and get the waste products out.

Division of the Cell Before it becomes too large, a growing cell divides forming two “daughter” cells. The cell copies all of its DNA and each daughter cell receives its own copy, so no “information overload”.

Cell division solves the problem of cells becoming too large. It keeps the ratio of surface area to volume where it needs to be. And The DNA gets replicated for the two new daughter cells.