Key area 4: Cellular
differentiation
Stem cells and meristems
Unit 1: DNA and the Genome
Cellular differentiation
Multi-cellular organisms are comprised of a
large number of cells. These are
specialised to carry out specific roles in
the body.
Differentiation is the process by which
unspecialised cells become altered and
adapted to form a special function in the
body.
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DNA and
the
Genome
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DNA and
the
Genome
Selective gene expression
Every cell in your body has all the genes
necessary for constructing the whole
organism.
Genes can be switched on or switched off
when they are required (see Unit 2)
otherwise the body would waste energy
producing proteins in cells where they are
not needed.
e.g. insulin produced in pancreas cells only,
DNA and
not in brain CFE
orHigher
heart
cells.
Biology
the
Genome
Differentiation in animals
Each human life begins life as a fertilised
egg (zygote) and divides to become
approximately 37.2 trillion (37 200 000 000 000)
With almost 200 different cell types.
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DNA and
the
Genome
In the embryonic cells all the genes are
switched on, or have the potential to be
switched on.
As development proceeds, the cells
undergo differentiation and become
specialised.
Once a cell has become specialised it only
expresses the genes that code for
proteins specific to the role of the cell.
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DNA and
the
Genome
Embryogenesis video clip
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DNA and
the
Genome
Stem cells
Stem cells are unspecialised cells that
can:
• Reproduce themselves by repeated
mitosis and cell division.
• Differentiate into specialised cells when
required to do so.
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DNA and
the
Genome
Embryonic stem cells
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DNA and
the
Genome
Embryonic stem
cells come from
very early embryos
(5-14 days after
fertilisation) called
blastocysts.
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DNA and
the
Genome
Embryonic stem cells have the potential
to differentiate into any type of cell
found in the human body
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DNA and
the
Genome
Tissue (Adult) stem cells
Tissue stem cells involved in maintaining
and repairing the body.
They have a narrower differentiation
potential than embryonic stem cells as
many of their genes are already
switched off.
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DNA and
the
Genome
Adult stem cells are
found at several
locations around the
body.
Hematopoietic stem cells
give rise to different
blood cells.
Mesenchymal stem cells
give rise to bone,
cartilage, adipose tissue.
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DNA and
the
Genome
Research and therapeutic value
of stem cells
Watch video on stem cell research
Collect the “All about Stem Cells” activity
pack. Divide the class into 4 groups (1 set of
cards per group).
Each group to make a poster answering the
“Your task” questions in each set.
Poster conference…make a summary of the
findings of each groups poster in your
DNA and
jotter.
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the
Genome
Growth and differentiation in
plants
In multicellular plants growth is
restricted to regions called meristems.
These are groups of unspecialised plant
cells capable of dividing through out the
life of the plant.
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DNA and
the
Genome
Types of meristem
Apical meristem at
the tip of the root
and the shoot –
adding length to the
plant.
Lateral meristems
allow the stems to
thicken.
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DNA and
the
Genome
1. Apical meristem
• Found at the tip of the root and shoot.
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DNA and
the
Genome
2. Lateral meristem
• Inside the plant.
• Called cambium.
• Produces new vascular bundles (xylem
and phloem) to transport food and
water in the stems of perennial plants.
• Each year it forms it produces an annual
ring of xylem. The number of rings
indicates the age of the plant.
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DNA and
the
Genome