Transcript 2.2 The Importance of Cell Division

2.2 The Importance of Cell
Division
Farah F.
Cell must divide because there is a
limit to how large they can grow!
• Nutrients and waste enter and exit the cell
through the cell membrane
• As a cell gets larger the amount of material in
the cell increases faster than the cell
membrane can grow
• After a while nutrients and waste can’t pass
through the membrane in the amounts
required and the cell dies
Cell Division allows an organisms growth,
maintenance (repair damage), and its
reproduction. From one cell two new cells are
created
• Growth: enables organisms to grow from a single cell
to a multi-celled organism
– Multicellular organism: made up of more than one cell
• grows by increasing their number of cells through cell division
• Maintenance: new cells are produced to replace
worn-out or dead cells and regenerate damaged tissue
• Reproduce: create new offspring through simple cell
division or the joining of special cells called gametes
(egg, sperm)
Cell Division for Growth
Why can’t cells just get larger? Why must they
make more copies of themselves and divide?
– This is because cells obtain nutrients and get rid of
wastes:
• Diffusion: movement of substance from an area of
high concentration to low concentration
• Osmosis: movement of water from an area of high
concentration to low concentration
• If a cell is too large these processes will not work
properly
Cell Division for Repair and
Replacement
– Old or damaged cells are replaced
• When you cut your finger, the damaged
cells will be replaced by healthy cells around
the cut dividing and making copies of
themselves
• Bone cells divide to repair broken bones
– Some organisms can even regenerate parts of their
body!
• A gecko can re-grow its tail!!!
Cell Division for Reproduction
• Asexual reproduction: producing offspring using only one
parent
• Have the EXACT same DNA as their parent (clones)
• Sexual Reproduction: producing offspring using two parents
– Occurs when sperm from one parent
fertilizes the egg of the other parent
– Offspring get half their genetic info from
one parent and have from the other