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B io Factsheet
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Number 238
Stem cells: research, potential, and the law
Fig 2. Development of embryonic and adult stem cells
What are stem cells?
There are two types of stem cells: embryonic stem cells, and adult
stem cells.
Fertilised egg
In humans, embryonic stem cells are formed when an egg, which
has been fertilised by a sperm, divides to from new cells.
Five days after fertilisation, the embryonic stem cells become a
blastocyst, comprising the inner cell mass - which develops into
the embryo - and an outer layer of cells known as the trophoblast which goes on to form the placenta (Fig.1).
Totipotent
embryonic stem cells
Fig 1. Blastocyst
Inner cell mass
Pluripotent
embryonic stem cells
Blastocyst
blastocyst
cavity
Embryonic
development in
uterus
trophoblast
Embryonic
development
in laboratory
(up to 14 days)
Immediately after fertilisation, the embryonic stem cells which are
produced during the first few days of embryonic development are
described as totipotent i.e. they are capable of developing into any
of the different cell types found in the human body. After the
formation of the blastocyst, the embryonic stem cells of the inner
cell mass become pluripotent. They can still form any of the different
cells in the adult human body, but as they can no longer become
cells that form the trophoblast, they can no longer be described as
totipotent.
Long term
culture of
stable human
embryonic
stem cell line
Adult stem cells
blood brain muscle
stem stem stem
cell
cell
cell
Why is stem cell research in the news so much?
Stem cell research holds huge potential for allowing scientists to
better understand how the human body works, and therefore to
develop better treatments for when things go wrong. However,
because stem cells theoretically have the potential to form an entire
human being, the use of these cells in research is also highly
controversial.
The cells of the inner cell mass then go on to develop into adult
stem cells. Adult stem cells are multipotent; they can still develop
into multiple cell types, but can only produce cells with a related
function. For example, multipotent adult blood cells are capable of
producing all the different blood cells in your body, but not hair
cells, skin cells, or muscle cells.
Potential benefits of stem cell research
Already, direct transplants of stem cells from one person to another
are being used to treat cancer. Over 7,000 people are diagnosed in
the UK every day with leukaemia (cancer of the blood) – which is
equal to almost 19 people every day. By replacing the defective
blood stem cells of the patient with those from a healthy donor, the
symptoms can be relieved.
The embryonic stem cells used in scientific research are extracted
from the inner cell mass of blastocysts. These cells can be put into
a laboratory environment which encourages them to continue to
develop into embryos, or alternatively, the cells can be used to
generate stable cell lines which remain in a stem cell-like state.
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Bio Factsheet
238 Stem cells: research, potential, and the law
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Additionally, work in the laboratory involving human embryonic
stem cells is currently being used to:
Typical Exam Question
(a) How do adult stem cells differ from embryonic stem cells? (2)
(b) Suggest two advantages of using adult stem cells rather than
embryonic stem cells (2)
1. Test new drugs. Stem cells taken from patients with specific
diseases can be used to trial new drugs for these diseases before
testing them in animals or humans.
(a) adult stem cells are pluripotent/ ultipotent/can only develop
into certain cells;
embryonic cells are totipotent/ can develop into any kind of
cell
(b) easier to obtain;
can use patient’s own stem cells therefore no immunity problem;
avoids the ethical issues associated with using embryonic stem
cells;
2. Increase our knowledge of early human embryonic development.
By understanding this process better, scientists and doctors
could identify abnormalities during embryonic development
that could potentially lead to problems during pregnancy or
early childhood.
3. Understand how a stem cell develops into a different cell type.
This process is known as differentiation. As stem cells
differentiate, they switch off genes required for stem cell activity,
and switch on genes required for specialised cell functions – for
example, genes that allow a nerve cell to sense pain. If scientists
can work out which genes are switched on to produce which
different cell types, this information could potentially be used
in the future to turn stem cells into new replacement organs for
patients requiring transplants as a result of injury or disease.
Markscheme
What are the rules regarding human stem cell research
in the UK?
Typical Exam Question
Human stem cells used in research are derived from embryos. Because
embryos have the potential to become a human being, there are
strict rules which scientists have to follow if they want to do research
using human embryonic stem cells.
Firstly, any research using embryonic stem cells has to be approved
by the government. This will depend on:
1. Where the embryo comes from
2. The reason for the research
The diagram below shows two different stem cells and the
differentiated cells that they can form.
Sources of embryos
stem cell X
red blood cell
Currently, human embryonic stem cells can only be used for research
if they come from an embryo which was created outside the human
body. In most cases, these embryos are created in a laboratory for
couples that are unable to have a baby naturally. This process is
known as in vitro fertilisation (IVF). Because IVF is highly
inefficient, more embryos are created in the laboratory than are
used by the couple. Most human embryonic stem cell lines in use in
the UK are produced from these surplus embryos – but this can
only be done if the couple that donate the sperm and egg give their
permission.
stem cell Y
many other
cell types but
not embryonic
cells
Research using human embryonic stem cells that IS
allowed in the UK
Scientists are allowed to do experiments on human embryos and
embryonic stem cells for the following reasons:
1. To find out more about human embryonic development
2. To understand more about human diseases
3. To use this knowledge to develop treatments for human diseases
(a) State one site where stem cell X may be found in an adult
human (1)
(b) Explain why stem cell B is described as pluripotent (2)
(c) Explain how genetically identical cells produced from stem
cells can have quite different functions (2)
(d) Suggest why you might decide to keep a supply of live
stem cells from your brain in a laboratory (2).
Research using human embryonic stem cells that is
NOT allowed in the UK
(a) bone marrow e.g. of long bones / ribs);
(b) it can give rise to many different types of cell;
but not embryonic cells;
(c) cell function is determined by which genes are switched on
or off/ genetically identical cells will have different genes
activated so have different functions;
ref to transcription factors/promoters etc;
(d) they would be genetically the same as the rest of your cells;
allowing you to replace damaged brain cells if you had an
accident/suffered brain deterioration;;
you would be able to replace more than one kind of brain
cell;
in perpetuity;
Embryos can be produced by fertilising an egg cell with a sperm
cell. Embryos can also be produced by other methods, which
scientists can use to create embryos with the genes they are
interested in. In theory, these techniques could be used to create
designer babies, or embryos with specific genes (e.g. for blonde
hair or brown hair). It is illegal to produce a child using these
techniques in the UK.
What is the future for stem cell research?
Stem cells are able to differentiate into any cell type found in the
human body. Recently, scientists around the world have discovered
that it is possible to reverse this process – to turn an adult cell back
into a stem cell.
.Markscheme
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Bio Factsheet
238 Stem cells: research, potential, and the law
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Why would you want to turn an adult cell back into a
stem cell?
(d) Complete the table below (6)
Arguments for the use of
embryonic stem cells to
produce tissues
Currently, many organ transplants are unsuccessful because the
patient’s body recognises the donated organ as a foreign object,
and fights the transplant as though it was an infection.
Arguments against the use of
embryonic stem cells to
produce tissues
If scientists are able to work out:
a) How to turn an adult cell back into a stem cell
b) How to turn stem cells into specific organs
...then it could be possible to take cells from an adult human and
produce a new organ specifically for them, using their own cells.
Because the DNA of the new organ matches the DNA of the patient,
the risk of the body rejecting the transplant is reduced.
Additionally, creating stem cells in this way would remove the ethical
objections to using embryos created by IVF to produce stem cells
for research, as this process does not involve loss of an embryo
which has the potential to form a human being.
This technology holds the potential to revolutionise the field of
stem cell research, creating a plentiful supply of ethically acceptable
human stem cells. Currently, this research is in its early stages. But
watch this space...
Step 6
cells stop dividing and
differentiate
human tissues for
transplantation
Markscheme
Step 7
1. (a) cells which can divide;
and differentiate into many different types of cell;
(b) (i) IVF/superovulation;
(ii) Blastocyst;
(c) can use patient’s own stem cells therefore no immunity
problem;
overcomes problem of shortage of donors;
less invasive technique/ less life threatening / reduced
recovery time;
may be cheaper;
stem cells cultured in sterile
petri dish
(d)
Step 5
Arguments against the use of
embryonic stem cells to
produce tissues
stem cells isolated, rest of
blastocyst discarded
Arguments for the use of
embryonic stem cells to
produce tissues
Step 4
Objection on religious/ethical
grounds/ Increases pressure on
women to produce surplus
embryos
grown to form blastocyst
Potential for culturing
patient’s own cells to
provide replacement tissues/
organs or alleviate suffering
Step 3
Embryonic stem cells are potential
babies/people
Spare embryos
Embryos should not be
considered human at this
stage
Step 2
Ref to unexpected harmful effects/
Problems with regulation/ ref to
designer babies
Fertilisation of egg with sperm
Stem cells from IVF would
otherwise be discarded
Step 1
Research into the use of
embryonic stein cells is
unnecessary as it will soon be
possible to use non-embryonic
stem cells
(a) What are stem cells? (2)
(b) The diagram shows how embryonic stem cells may be used to
produce human tissues.
Use of non-embryonlc cells
will need a development
phase that used embryonic
cells
Practice Question
(i) Suggest the likely source of ‘spare embryos’ (1)
(ii) At what step do the cells lose their totipotency? (1)
(c) Suggest two advantages of using stem cells rather than an organ
transplant (2).
Acknowledgements:
This Factsheet was researched and written by Bryony Graham
Curriculum Press, Bank House, 105 King Street, Wellington, Shropshire, TF1 1NU.
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