Differentiation and Stem Cells Higher Human Biology Unit 1
Sub-Topic 1 (a)
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Learning Outcomes o Differentiation: During embryological
development the unspecialised cells of the early embryo
differentiate into cells with specialised functions. o Stem cells:
Stem cells are relatively unspecialised cells that can continue to
divide and can differentiate into specialised cells of one or more
types. o In the very early embryo, embryonic stem cells
differentiate into all the cell types that make up the organism. o
Tissue (adult) stem cells replenish differentiated cells that need
to be replaced and give rise to a more limited range of cell types.
o Tissue (adult) stem cells in the red bone marrow give rise to red
blood cells, platelets and the various forms of phagocytes and
lymphocytes. o Once a cell becomes differentiated it only expresses
the genes that produce the proteins characteristic for that type of
cell.
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Introduction The human body is made up of many specialised
cells that perform specific functions. Specialised cells arise from
the differentiation of unspecialised cells during embryological
development. Differentiation is when an unspecialised cell becomes
specialised in structure and biochemical properties, making them
perfectly adapted for carrying out a particular function.
http://www.educationscotland.gov.uk/highersciences/humanbiology/animations/stemce
ll.asp
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Examples of Differentiation
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Ciliated epithelial cells line the trachea (windpipe) It has an
axon (a long, insulated cytoplasmic extension). This structure is
perfectly suited for transmitting nerve impluses. This is because
those cells are only expressing the genes for neurotransmitters.
motor neurone cell They are perfectly suited to their job of
sweeping dirty mucus up and away from the lungs. This is because
those cells are only expressing the gene that codes for mucus. This
means that the mucus gene is switched on and other genes, like the
one that codes for insulin, are switched off.
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Stem cellswhat do you know already? Use the questions below to
help you complete a KWL chart to show the following information: K
what you know already W what you want to learn about stem cells
during this unit L complete this at the end of the unit to
summarise what you have learned Some questions to think about What
is a cell? What varieties of cell exist? What is a tissue? Give
some examples. What is an organ? Give some examples. What is a
system? Give some examples. What is a stem cell? What are some
different types of stem cells? What is the purpose of stem cell
research? What are some ways that stem cells have been successfully
used in medicine? What are some of the issues in stem cell
research? What are some of the misconceptions that people have
about stem cell research?
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What are stem cells? Stem cells are unspecialised cells that
have the ability to reproduce and differentiate into a diverse
range of specialised cells.
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Types of stem cells Embryonic Adult
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Embryonic stem cells Embryonic stem cells are derived from an
embryo about 45 days old (bastocyst). These early embryonic cells
have the ability to differentiate into all of the cell types that
make up an organism - pluripotent
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Adult (tissue) stem cells Adult or tissue stem cells are found
in small numbers in the tissues and organs of adults and children,
including the brain, bone marrow, skeletal muscle and skin. These
cells give rise to a much more limited range of cell types and will
tend to develop into cell types that are closely related to the
tissue in which they are found. They are multipotent. These cells
replenish differentiated cells that need replaced in the tissues in
which they are found.
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Example of Adult Stem Cells
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Other types of stem cells Stem cells can also be taken from the
umbilical cord of new babies. Like adult stem cells, these cells
can differentiate into a limited range of specialised cells.
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Induced pluripotent stem cells Induced pluripotent stem cells
are adult cells that have been genetically reprogrammed to an
embryonic stem cell-like state.
http://www.bbc.co.uk/news/science-environment-19878542
http://www.bbc.co.uk/news/science-environment-19872346
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Questions 1.Define the term differentiation. 2.In what way is a
ciliated epithelial cell a good example of a specialised cell? 3.A
goblet cell in the lining of the trachea produces mucus but not
insulin. Explain briefly how this specialisation is brought about
with reference to genes. 4.Give two characteristics of stem cells.
5.Name two types of stem cells found in humans. 6.For each type of
stem cell (Q5), identify one location where these cells can be
found. 7.Which type of stem cell is capable of differentiating into
all the types of cell that make up the organism to which it
belongs?
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Answers 1.Unspecialised cells of the early embryo become
specialised in structure and biochemical properties, making them
adapted for carrying out a particular function. 2.They are a good
example as they are perfectly suited to their job of sweeping dirty
mucus up and away from the lungs. 3.The cell is now only expressing
the gene that codes for mucus/ only the mucus gene is switched on.
The gene that codes for insulin is switched off. 4.Two
characteristics of stem cells are 1.They reproduce themselves by
repeated mitosis 2.They can differentiate into specialised cells.
5.Two types of stem cells in humans are 1.Embryonic 2.Adult
6.Embryonic stem cells are found in embryo blastocysts, Adult stem
cells are found in bone marrow, skin, skeletal muscle, brain.
7.Embryonic