THE IMPORTANCE OF CELL DIVISION Cell Rap THE IMPORTANCE OF CELL DIVISION SNC 2PI April 2011

In the beginning ... You started life as a single cell: Now your body is made up of TRILLIONS of cells How does a single cell become a full-grown multicellular organism? A fertilized egg

Why do cells divide? Cells divide for three reasons: Reproduction Growth Repair

Cell Division for Reproduction All cells, including single-celled organisms use cell division to reproduce Single-celled organisms reproduce by the process of asexual reproduction: Involves only one parent Offspring are exact genetic copies of the parent Multi-cellular organisms reproduce by the process of sexual reproduction: Two parents involved Cell from one parent joins with cell from another parent Offspring inherit characteristics from both parents

Cell Division for Growth As multi-cellular organisms grow, the number of cells increases Why does the number of cells increase instead of simply increasing the size of the cells? The answer lies in how a cell uses chemicals to function

Cell Division for Growth All cells require a few things to survive: A source of energy Nutrients Water Certain gases (such as oxygen) How do these chemicals that are needed travel into the cell to where they are used? Diffusion is the transport mechanism by which chemicals move into and out of the cell Chemicals move from areas of high concentration to low concentration

Cell Division for Growth Concentration is the amount of substance (solute) in a given area Water enters and leaves the cell by the process of osmosis Osmosis is the movement of water towards an area of high solute concentration

Cell Division for Growth So back to the question ... Why does the number of cells increase as an organism grows? Diffusion and osmosis take time If a cell get too large, important chemicals and water may not move through the cell fast enough for the cell to function properly

Cell Division for Repair Your body must continually replace cells in order to survive: Every day you shed MILLIONS of dead skin cells All of your red blood cells are replaced approximately every 120 days If you break a bone, your cells divide to heal the break If you cut yourself, new cells need to be made to fill the gap

Textbook Questions Answer ‘Check Your Learning’ questions 1 – 6 on page 37

Pg. 37 # 1 – 6 Name three reasons for cell division. Cell division for reproduction Cell division for growth Cell division for repair A cleaning product claims to kill ‘99.9% of all bacteria.’ Will a cleaned surface stay bacteria-free forever? Explain your answer. The surface will not stay bacteria-free forever, because if a single bacterium is left alive, it can reproduce to a large number in a short period of time.

Pg. 37 # 1 – 6 List three differences between asexual and sexual reproduction. Asexual Reproduction Sexual Reproduction One parent Two parents Offspring identical to parents Offspring share characteristics of both parents Does not involve cells joining together Involves two ‘half-cells’ joining together

Pg. 37 # 1 – 6 What processes are responsible for chemicals moving into, throughout and out of cells? Diffusion and osmosis are responsible for moving chemicals into, throughout and out of cells. Why do cells divide instead of just getting bigger, as an organism grows? Important chemicals must be available to all parts of the cell. If a cell gets too large, the chemicals may not be able to move fast enough for the cell to survive.

Pg. 37 # 1 – 6 A minor wound heals over time. Explain how this happens. Cell division creates new cells that replace those in the wounded area to close and heal the wound.