National 4 & 5 BIOlogy – multicellular organisms

National 4 & 5 Biology –
multicellular organisms
Section 2a – Stem Cells
• How do we get all
these different
cells from 1
original cell?
• How have they
become so
different to each
Learning Outcomes
• Today we will learn:
• - the site of production of specialised cells in
• - the role of stem cells in growth & repair
• - potential uses of stem cells & ethical issues
related to these
How did you get like this?
By the time you finish growing, you will have an estimated 50 trillion cells. That’s
You started out as a single cell. How did one cell turn into 50 trillion?
A slow start
For the first week the fertilized egg cell (zygote) splits in two every day to make a bundle
of smaller cells.
cell division
After about 1 week, the zygote is called an embryo.
Exponential growth
What are stem cells?
The first cells are stem cells. These 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.
Embryonic Stem Cells
• - found in newly formed
• - they can become placenta
cells or more embryo cells
• - after 4-5 days a ball of embryo
cells is formed – blastocyst
• - these cells can become any
type of human cell
• - they are pluripotent
• - after about a week, they will
start specialising
Changing cells
When the embryo contains about 500 cells, the cells stop being the same and they stop
getting smaller with each division. They start to differentiate into different types of cell.
At this point, stem cells no longer form two new stem cells when they divide. Instead, one
of the two daughter cells becomes a tissue cell.
stem cell
stem cell
tissue cell
What is a stem cell?
Stem cell
Identical stem cells
Stem cell
Specialized cells
Becoming specialized
Tissue cells continue to divide and
differentiate, each time becoming
more and more specialized.
stem cell
tissue cells
Some will become nerve
cells, others will become
blood cells, muscle cells,
bone cells, etc.
nerve cells
red blood
cardiac muscle
Embryonic & Foetal Stem Cells
• Cells in a blastocyst will initially specialise
into one of three layers
• - Endoderm (“endo” = inner)
• - forms many internal organs – e.g. stomach,
intestines, liver
• - Mesoderm (”meso” = middle)
• - forms the muscles
• - e.g. heart , skeleton, connective tissue, deep
layers of skin
• - Ectoderm (“ecto” = outer)
• - forms the central nervous system, and body
surface layers
• Once part of these layers, cells will have
started to specialise
You will each be assigned a cell type
Around the room there will be three stations:
- ectoderm
- endoderm
- mesoderm
You must decide which of the three stations you
belong in (others in the group can help)
• Your group must then decide which body systems
are within your layer
Adult Stem Cells
• - in adults, stem cells are
found within many tissues of
the body
• - can form specialised cells of
a particular tissue
• - e.g. Hematopoietic cells can
form any type of blood cell
• - adult stem cells can only
form cells of a certain type
• Stem Cells Video
• Stem Cell therapies video
Re-Cap task
Produce a summary of stem cell research:• What are the main types of stem cell and
where do they come from?
• What are scientists using stem cells for?
• What breakthroughs could be possible thanks
to stem cell research?

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