10-1 Cell Growth Vocabulary: Cell Division Key Concept: What problems does growth cause for cells?

Does an animal get larger because each cell increases in size or because it produces more cells?……

Living Things Grow by… producing more cells. (For example: cells of an adult animal are the same size as those of a young animal) BUT Why not just keep growing in size? Why aren’t people just 1 big cell?

Two Reasons Why a Cell Divides Rather Than Continues to Grow Bigger: 1. More demands placed on the cell’s DNA Ex: a small town library has enough books for people to borrow but if a lot of people move into the town not enough books so, some people may have to wait for popular books. Larger cells would have to make greater demands on its small “genetic library” In time, the cell’s DNA is no longer able to serve the needs of a growing cell!

Two Reasons Why a Cell Divides Rather Than Continues to Grow Bigger: 2. More trouble moving enough nutrients & wastes across the cell membrane Rate materials enter and exit the membrane depends on surface area and cell volume...

the rate of exchange for food, H2O, and oxygen across a cell's membrane depends upon the cell’s SURFACE AREA   how quickly these materials are used by the cell depends upon the VOLUME of the cell Understanding these two concepts will help us understand why cells must divide in order to grow….

SURFACE AREA & VOLUME DO NOT INCREASE AT THE SAME RATE & THIS IS A PROBLEM FOR THE CELL! example: traffic increases as size of city increases, but the roads stay the same

(SA = Surface Area) ex: 1cm 2cm SA= length x width x # of sides   1cm 2cm SA= length x width x # of sides SA= 6cm2 SA= 24cm2 Volume= 1cm3 Volume= 8cm3  SA/Volume ratio= 6:1 SA/Volume ratio= 3:1 (SA = Surface Area)

The volume increases much more rapidly than the surface area, causing the SA/VOL ratio to decrease... the lower the SA/Volume ratio, the harder it is to get materials into/out of the cell the 2 cm cube is too large to efficiently move nutrients and waste in and out of the cell...

To solve this problem cells divide in a process is called… Cell Division The process by which a cell divides into 2 daughter cells Cell replicates (copies) all of its DNA each cell will get a copy of the DNA This solves the DNA problem as well as reducing the cells volume so that materials can exchange across the membrane