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THE IMPORTANCE OF CELL
DIVISION
Science 9
Where do cells come from?
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New cells come from pre-existing cells through the
process of cell division
This is how dead and damaged cells are replaced
in the human body
Functions of Cell Division – Healing and
Tissue Repair
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Every second of your life, millions of cells are
becoming damaged or dying in the human body
They constantly need replacing
Some of the activities we undergo remove these
cells such as washing, getting dressed, rubbing
hands on your clothes, etc.
Functions of Cell Division - Growth
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As the number of cells increase in a living thing, so does
its size
Human growth begins with the division of a fertilized
egg cell
All cells are approximately the same size
They need to divide because if they continued to grow,
they would not be able to acquire all the materials they
would need to survive
Also, the distance the nucleus is from all other parts of
the cell must be kept at a minimum so that messages
can be translated quickly and efficiently
Functions of Cell Division - Reproduction
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Cell division promotes life
Cell division in unicellular organisms like bacteria
produces two more organisms
Cell division is also critical for reproducing
multicellular organisms
Cell Division
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There are approximately 100 trillion cells in the
human body
However, it began as a single fertilized egg
It divided into two cells and so on until you were
produced
The Cell Cycle – step 1
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There are two phases of cell division: when it is
dividing and when it is not
The actual phase where it divides is small compared
to the other events that take place within the cell
The stages between cell divisions is called
interphase
During this time, cells take in nutrients, which are
important for energy, growth, and repair of the cell
The Cell Cycle – step 2
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A phase of rapid growth occurs
This is a period of interphase because cell division is
not occurring
The Cell Cycle – step 3
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The cell prepares for division by duplicating its
chromosomes within the nucleus (replication)
This must occur before cell division
The chromosomes contain all the important
information needed for the cell to survive
This is also a period of interphase
The Cell Cycle – step 4
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Another period of growth and preparation for cell
division occurs
Again, this is a period of interphase
Mitosis
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Most cells divide the same way
All cells divide into two cells – a mother cell
produces two daughter cells
The division of information in the nucleus and the
sharing of cytoplasm by moving to opposite ends of
the cell is called mitosis
Cytokinesis
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Cell division continues with the separation of
cytoplasm and its contents into equal parts
This begins before mitosis is complete
Half of the cytoplasm, containing half of the
organelles, goes to each daughter cell
This process differs between plants and animals
Cytokinesis – Plants and Animals
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In plants, a cell wall forms along the middle of the cell,
creating two new cells
In animals, the cell membrane pinches together in the
middle, separating the cytoplasm into two equal parts
Both daughter cells grow and develop complete
organelles during interphase
They will also make a copy of genetic material
The Phases of Mitosis
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Interphase
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Prophase
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Each chromosome splits and moves to opposite ends of the cell
Telophase
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Double-stranded chromosomes line up in the middle of the cell
Anaphase
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Individual chromosomes (two strands of information) becomes
visible
Metaphase
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cell grows and duplicates genetic material
A nuclear membrane forms around each strand; cytokinesis
begins
Interphase
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Cell continues to grow and duplicates its genetic material
Videos
The Cell
http://www.youtube.com/watch?v=X6N82No4Nz8
Mitosis
http://www.youtube.com/watch?v=L0k-enzoeOM