10-1 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”

P/S: how is DNA like a library?

Surface area/ volume

• A 1 mm3 cell has 6:1 ratio of surface area to volume• 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

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 orsomething small?

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 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?

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

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

amoeba Human cheek cells