Objective: To understand SA:V ratio and why a cell needs to divide.

Why a cell divides

Cell Growth: Grow by dividing instead growing larger

The larger a cell is the more demand is put on DNA and nutrients can’t move through big cells easily

Why a cell divides

DNA: Enough info. For a small cell, but if cell got too big there would be an info shortage

Ex: small town library would not be useful to a big city

Why a cell divides

Exchanging materials:Materials enter/leave by moving through the membrane

The rate of exchange depends on how much surface area the rate of materials needed depends on volume.

Understand SA:V ratio

Surface area:cell membrane (candy coating on M and M)

Volume: cell contents (chocolate center in M and M)Surface area to volume ratio:

Take the surface area (in cm2) and divide by volume (in cm3)

Figuring SA:V

If a side is 1 cm and there are 6 sides the SA would be 6*1cm2= 6 cm2

V would be 1cm3= 1cm3

SA:V= 6:1 or 6/1

Why a cell divides

Volume increases more rapidly than Surface area, The SA:V decreases—this can cause serious problemsTo keep SA:V at a normal ratio:Cell Divides A Cell will form 2 daughter cells1st: cell copies DNA2nd: cell divides

Now each daughter cell has an increased SA:V ratio