The document discusses cell division. It asks questions about how many cells compose an organism, when cells divide fastest and slowest, and if cells ever stop dividing. It explains that cells divide because their volume increases faster than surface area, limiting nutrient absorption and waste removal. Cells divide for growth, repair, and in cancer. Division rates vary, from 12-24 hours for most mammalian cells to 20-30 minutes for some bacteria. Eventually, cells can only divide a certain number of times before programmed cell death occurs. The rate of cell division changes over a lifetime from greater than cell death in childhood to less than cell death in later years.

1. The Great DivideThe Great Divide
05/04

2. To Be Answered…To Be Answered…
THINK:
 How many cells are you composed of?
 When an organism grows bigger do you
get more cells or just bigger cells or both?
 When do your cells divide the fastest?
Slowest?
 Do cells ever stop dividing?
 Are all cells capable of division and
replacement?

3. Why Would a Cell Divide?Why Would a Cell Divide?
 As cells absorb nutrients and get larger, the
volume of the cell increases faster than the
surface area
 This means that a cell can no longer absorb
nutrients and get rid of wastes fast enough to
support its demands (volume)
 So what’s a cell to do?
Solution: divide in 2!
Surface area
for exchange
not great
enough to
support cell’s
needs

4. When Would a Cell Divide?When Would a Cell Divide?
 Growth
 Repair or Replacement
 Cancer
Different cells divide at different rates:
 Most mammalian cells = 12-24 hours
 Some bacterial cells = 20-30 minutes

5. Getting Older…Getting Older…
 All cells are only allowed to complete a
certain number of divisions
 Then they die (programmed cell death)
How does cell division change over a lifetime?
 Childhood = cell division > cell death
 Adulthood = cell division = cell death
 The Later Years = cell division < cell death

6. Getting Older…Getting Older…
 All cells are only allowed to complete a
certain number of divisions
 Then they die (programmed cell death)
How does cell division change over a lifetime?
 Childhood = cell division > cell death
 Adulthood = cell division = cell death
 The Later Years = cell division < cell death