Section 10-1 Notes: CELL GROWTH

Section 10-1 Notes: CELL GROWTH

DNA “Overload”

Remember, the information that controls a cell’s function is stored in a molecule known as DNA. The larger a cell becomes the more demands the cell places on its DNA. In time, the cell’s DNA would no longer be able to serve the increasing needs of the growing cell.

Exchanging Materials

There is another reason why the size of cells is limited. Remember, nutrients enter a cell through the cell membrane and wastes leave through it. How fast this happens depends on the surface area of a cell, which is the total area of its cell membrane. If there is a large volume, the cell produces more wastes and needs more nutrients than can be moved across the relatively small area of the cell membrane.

A cell has more trouble moving enough nutrients and wastes across the cell membrane because the volume increases faster than the SA of the membrane.

Ratio of Surface Area to Volume

Length x width x # of sides = Surface Area (square units)

Length x width x height = Volume (cubic units)

Small cells have a HIGH ratio of SA/V which is good.

Large cells have a LOW ratio of SA/V which is bad.

To obtain the RATIO of surface area (SA) to volume (V), divide surface area by volume.

The equation is: SA/V

If you double or triple the surface area, you will notice that volume increases much more rapidly that the surface area, causing the ratio of SA to V to decrease. This decrease is bad! It can cause serious problems for the cell.

Think of it like this (the cell as a town): Suppose a small town has a 2 lane main street. As the town grows, more people will begin to use this street. The main street leading through town, however, has not increased in size. As a result, people will encounter more traffic as they enter and leave the town. A cell that continues to grow larger would experience similar problems.

DIVISION OF THE CELL

Before it becomes too large, a growing cell divides, forming 2 smaller “daughter” cells. This process is called cell division.

Before cell division can happen, it replicates, or copies, off all its DNA. This copying of the DNA solves the problem of information storage because each daughter cell gets one complete set of genetic information.