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Stem Cells
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What are stem cells?
Stem cells are unspecialized
cells capable of developing into
many different types of cell.
Stem cells found in embryos are
called embryonic stem cells
and develop into all the different
types of cell in the body.
Adults also contain stem cells.
These are found in small
numbers in many organs,
including bone marrow, brain,
skin and muscle.
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Embryonic stem cells
Up until the eight cell stage, all of the cells in a human
embryo are identical. At this stage, these stem cells
are unspecialized and can therefore differentiate
into many different types of cell.
After the eight cell stage, most of the
embryonic cells become specialized
and can no longer differentiate.
Some will become nerve cells, others
will become blood cells, muscle cells,
bone cells, etc.
nerve cells
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red blood
cells
cardiac muscle
cells
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Adult stem cells
Adult stem cells are found in small
numbers in many organs and tissues,
such as bone marrow.
Adult stem cells normally maintain and
repair damaged tissue, and, unlike
embryonic stem cells, can usually only
make a small number of cell types.
For example, adult stem cells in the
skin only normally form skin cells.
Research has shown that some adult stem cells can be
manipulated to produce many different cell types (e.g. brain
stem cells can make muscle cells). This is called plasticity.
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Plant stem cells
Plants also have stem cells. Plant cells can differentiate to
form specific cells throughout the plant’s life. Animal cells
lose this ability early in their life cycle.
Unspecialized plant cells are found in tissues
called meristems. Plant stem cells can
become specialized to form tissues such as:
 xylem: these cells transport water
and minerals up the stem from the
roots to the shoots and leaves
 phloem: these cells transport sugars,
produced in the leaves, up and down the stem.
These new types of tissue can be found in the
flowers, leaves, stems and roots of the plant.
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Stem cells – true or false?
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Super starfish!
What do plants and starfish have in common?
Chop the stem of a plant and it will grow back. What’s more,
the cut stem can grow into a completely new plant.
The same is true of the starfish! If it loses an arm to a
predator, it will grow back.
Even better, if the
predator manages to
eat everything but the
arm, a new individual
can grow out of the
remaining arm!
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Animal regeneration
Why can a starfish regenerate missing limbs?
The starfish contains stem cells that can divide, differentiate
and produce new tissues to replace those that are lost.
Humans and most other
animals cannot do this, but
scientists are studying how
stem cells could be used to
create new tissue and even
new organs to treat disease,
injury and conditions such
as paralysis.
What type of stem cells should be used?
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A controversial source?
Most stem cell research has used cells obtained from
embryos left over from fertility treatment.
These are called embryonic stem cells
(ESCs) and are the most powerful type
because they can turn into any type of cell.
Their use in research is strongly criticized
by people who believe it is unethical to
kill embryos for their cells.
Work involving embryonic stem cells
is subject to government regulation.
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If you ran the country…
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Therapeutic cloning
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How could adult stem cells be used?
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Advantages of using adult stem cells
Adult stem cells are not as powerful as embryonic stem cells,
but they do have other advantages.
 They come from volunteers so they are more ethically
acceptable.
 A patient’s own stem cells could be used to treat their
own disease, avoiding the problem of immune rejection.
 It might be easier to guide their development into
specific cell types.
 They are less likely to become cancerous.
There is a great deal of research into using adult stem cells to
treat diseases. They could reduce the need for organ
transplants, which have long waiting lists.
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Glossary
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Multiple-choice quiz
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