1. Limits to cell growth

2. Why does a cell divide? 1. The larger a cell becomes, the more demand on its DNA. 2. Cell has more trouble moving nutrients and wastes across the cell membrane

3. DNA ‘overload’ As a cell increases in size, the DNA does not make more copies Result: too many demands on it’s genetic “library”

4. Exchanging materials The rate at which food can enter the cell and wastes be removed from the cell depend on it’s surface area to volume ratio. The larger a cell, the harder it is to move materials in and out

5. Surface area/volume A 1 mm 3 cell has 6:1 ratio S.A./Vol A 2 mm 3 cell has a 3:1 ratio “ “ A 4 mm 3 cell has a 2:1 ratio “ “ The smallest cell has the highest ratio

6. Cell division Before it becomes too large, a cell divides, forming 2 “daughter” cells. The DNA is replicated, or doubled, before a cell divides Anaphase: DNA migrates to daughter cells

7. “Daughter” cells Each new cell has a full set of DNA, its genetic information The cell size has been reduced, increasing its surface area/volume ratio Materials can now be exchanged efficiently

8. Growth by cell division All multicellular organisms grow from a single cell. They grow by cell division Even though the size of living things varies greatly, their cells are all about the same small size. Giant sequoia redwood, the world’s largest living thing