limits to cell growth. why does a cell divide? 1. the larger a cell becomes, the more demand on its...
TRANSCRIPT
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