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CELLULAR REPRODUCTION – Ch. 9
 As the cell grows, its volume increases much more rapidly than the
surface area.
 The cell might have difficulty supplying nutrients and expelling
enough waste products.
 Diffusion over large distances is slow and inefficient.
 Small cells maintain more efficient transport systems.
Cell Cycle – sequence of growth and division (mitosis)
Why do cells divide?
 to grow larger
 to repair injuries
 to replace cells that die (skin cells, blood cells)
GROWTH
- Interphase (this is NOT a phase of Mitosis) –
 majority of the time – the cell is active and growing
 chromosomes are not visible
 chromosomes are duplicated to prepare for cell division
MITOSIS (division) –
 process of cell division in which the cell’s nuclear material divides
 4 phases 1. Prophase
 longest phase
 chromatin condenses into chromosomes – shaped like an X
 each part of the X is known as a sister chromatids
 two small structures called centrioles appear
 the centrioles are contained in the centrosome
 spindle fibers (made of microtubules) connect to the centrioles
 the nuclear membrane disappears
 centrioles migrate to opposite ends of the cell and spindle forms
between them.
 Many plant cells do not contain centrioles.
2. Metaphase
 short
 sister chromatids line up in middle (M) (middle = equator) of the
spindle
 the spindle is football shaped structure connecting the two
centrioles.
 each chromatid attaches to a spindle fiber
 at end the chromatids are pulled apart
3. Anaphase
 chromatids pulled to opposite poles (pulled Apart)
 the phase ends when each set of chromosomes reaches its centriole
4. Telophase (Two cells)
 spindle fibers disappear
 each set of chromosomes becomes enclosed in a nuclear membrane
 new cells begin independent existence
 CYTOKINESIS – cytoplasm divides and is pinched off to form 2
new cells
 each new daughter cell begins independent existence
 the daughter cells are identical with identical chromosomes
Plant cells
 cannot pinch in half because the cell walls are too thick so a
cell plate forms
 plant cells do not have centrioles
Cancer – uncontrolled growth and cell division.
 Crowd out normal cells resulting in loss of tissue function
 Cancer cells spend less time in interphase so they grow and divide
unrestrained.
 Caused by genetic change or damage
 Carcinogens – substances that are known to cause cancer
Apoptosis – programmed cell death – shrink and shrivel in a controlled
process.
Stem cells – unspecialized cells that can develop into specialized cells
under the right condition.
 Embryonic stem cells - After fertilization, the resulting mass of
cells divides repeatedly until there are about 100–150 cells.
These cells have not become specialized.
 Adult stem cells - Found in various tissues in the body and
might be used to maintain and repair the same kind of tissue
o Less controversial because the adult stem cells can be
obtained with the consent of their donor