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4
Cell replication
‘Spray-on skin’
ODD FACT
It has been estimated that each
person replaces, on average, 18
kg of skin cells during a
lifetime. Dandruff, skin cells
from our scalps, represents just
a fraction of the skin cells we
must replace.
Figure 4.4 ‘Spray-on skin’ or CellSpray, developed by Dr Fiona Wood.
Skin cells taken from a patient are cultured and allowed to replicate.
A suspension of these cells is sprayed onto burnt areas where they
continue to grow and form a new skin.
Nuclear division leads to
reproduction of cells
• Cells reproduce during the cell cycle.
• Cells can reproduce only if the genetic
material is replicated.
• The duplication of cells involves mitosis and
cytokinesis.
• The two newly formed cells each have the
same kind and amount of genetic material as
the parent cell.
• Each species has a characteristic chromosome
number.
How long is a cell cycle?
Figure 4.9 The total
time taken for
one mitotic cell
cycle can vary
greatly
from organism to
organism. Note the
checkpoints at
which there
appears
to be self-checking
to ensure that
mistakes have not
occurred during
the synthesis of
DNA or replication
of the cell.
• Mitosis occurs in a range of different tissues in
different plants and animals.
• Some eukaryotes reproduce asexually from a
single cell.
• Uncontrolled cell replication can lead to
cancers.
New liverworts from cells in a cup