Stem cells
Stem cells are cells found in most, if not all, multi-cellular animals. They are characterized by the
ability to renew themselves through mitotic cell division and can change into a wide range of
specialized cell types. They are found throughout the organism.
All cells in a particular organism have the same number of chromosomes with the same types of
genes .e.g. all human cells have 46 chromosomes with the same information on all of their genes.
How then can different types of cells be produced.?
A stem cell has all the genetic information available for a particular organism. To become one
particular, specialised cell a stem cell can switch off certain genes so that those genes do not affect
how the cell develops. If a stem cell is producing a different type of specialised cell then different
genes will be switched off and other will remain active. By this method multicellular organisms can
make many different types of cells to carry out different types of functions .e.g. if a stem cell were
to be changed into a red blood cell it would have the gene switched on that produces the protein
haemoglobin, the oxygen carrying substance. If making a hair cell this gene would obviously not need
to be switched on.
A cell that does not have a particular function is said to be undifferentiated. Therefore, stem cells
are undifferentiated cells. They have yet to be developed to perform a particular function. They are
found all over the body in animals.
Specialised cells produced from stem cells
Stem cells are important for living organisms for many reasons. In the 3- to 5-day-old embryo, called
a blastocyst, stem cells in developing tissues give rise to the multiple specialized cell types that make
up the heart, lung, skin, and other tissues. In some adult tissues, such as bone marrow, muscle, and
brain, specific groups of adult stem cells make replacements, by cell division for cells that are lost
through normal wear and tear, injury, or disease.
So there are two broad types of mammalian stem cells :

embryonic stem cells –found in developing embryos.
In a developing embryo, stem cells can differentiate into all of the specialised embryonic tissues

adult stem cells - found in adult tissues..
In adult organisms, stem cells act as a repair system for the body, replenishing specialized
cells, but also maintain the normal turnover of regenerative organs, such as blood, skin or
intestinal tissues.
Scientists believe that stem cells may, at some point in the future, become the basis for treating
diseases such as Parkinson’s disease, diabetes, and heart disease.
Answer the following questions after reading the information above.
1.What is a stem cell? _______________________________
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2.(a)What are the two main types found in humans?
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(b) Where are stem cells found in mammals?
3. Name 3 specialised cells or tissues found in embryos.
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4.What is the main function of stem cells in adults?
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5.Explain how genes are involved in specialisation of cells.
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6.Why is the study and understanding of how stem cells work important for scientists. _________