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Transcript
Chapter 2
2.3 – The Need for Cell Division
The Need for Cell Division
• All large plants and animals are composed of
many small cells rather than one large cell
• This is because there is a limit to how large cells
can grow
Is Smaller Better?
• Cells communicate using chemical messages
• Before a nucleus can tell the organelles in the
cytoplasm what to do, it must receive messages
from the cell’s surroundings
Is Smaller Better?
• The bigger the cell is, the longer messages take
to reach the nucleus, and for the rest of the cell
to receive instructions
• Cells must be small to receive these messages
quickly so they can react to changes in the
environment
Is Smaller Better?
• For example:
• Exposure to sunlight triggers a
chemical message to skin cells
• The message travels to the nucleus
of the skin cell
• The nucleus sends a message to
the ribosomes, telling them to
make melanin
• The melanin blocks sunlight,
preventing sunlight from damaging
cells below
Is Smaller Better?
• Cells also need a constant supply of nutrients
and waste must be removed
• Molecules enter into and out of cells through the
cell membrane
• The more cell membrane there is compared with
the volume of a cell, the more efficiently the cell
can take in nutrients and eliminate waste
Some Large, Some Small
• Some cells in your body are larger than others
• For example fat cells are larger than muscle cells
• If you compare the sizes of cells and their
functions you will find that cells that do a lot of
work are usually smaller than cells that are not
as active
Some Large, Some Small
• The more active a cell is, the more nutrients it
needs and the more waste it produces
• Many small cells are more efficient at
exchanging nutrients and waste than one large
cell