Limits to cell growth

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

DNA ‘overload’

• As a cell increases in size, the DNA does not make more copies

• Result: too many demands on it’s genetic “library”

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

Surface area/volume

• A 1 mm3 cell has 6:1 ratio S.A./Vol• A 2 mm3 cell has a 3:1 ratio “ “• A 4 mm3 cell has a 2:1 ratio “ “• The smallest cell has the highest ratio

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

“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

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