1. 10-1 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” P/S: how is DNA like a library?

4. Surface area/ volume A 1 mm 3 cell has 6:1 ratio of surface area to volume 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

5. Exchanging materials The rate at which food can enter the cell and wastes be removed from the cell depends on it’s surface area to volume ratio. The larger a cell, the harder it is to move materials in and out WB: which has a larger surface: volume ratio- something large or something small?

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 library. The cell size has been reduced, increasing its surface area/volume ratio. Materials can now be exchanged efficiently. P/S: are the 2 new cells exactly the same? Why or why not?

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

9. WB: which is larger ( in actual size), the cells of a unicellular or multicellular organism? amoeba Human cheek cells