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petak, 19.02.2010.
Amazing Cells!
Amazing Cells!
Did you know your body is made of trillions of cells? There
are millions of different types. Where did all of these
different types come from? Part of the answer is a special
type of cell called stem cells.
Many living things need stem cells including animals and
plants. An organism that is not fully developed is called an
embryo. In animal embryos, stem cells can develop into
different types of cells. Your body has over 200,000 different
types of cells. It has blood cells, muscle cells, skin cells, and
stomach cells just to name a few. Each type of cell has its
own structure and function.
The process of differentiation
All stem cells have some certain properties:
• Stem cells divide to make more stem cells.
• Stem cells also have the ability to develop into different types
of cells.
A stem cell divides into two daughter cells. Each daughter
cell is identical to the original parent cell. When mature,
these cells also divide. This is how embryos get a supply of
stem cells. A growing embryo needs a lot of stem cells to
develop tissues and organs. In the laboratory, starting with a
few stem cells, scientists have grown millions in a few
months.
So how do
stem cells
change into
other types of
cells?
Scientists are
studying this
problem.
Something called a signal tells stem cells to become different
types of cells. Genes are pieces of DNA that carry
information from the parent cell to the offspring cells. The
genes inside stem cells provide internal signals. The
environment outside of the cell provides external signals.
The cell's environment includes chemicals from other cells.
Different types of
specialized animal cells
There are two main types of
animal stem cells. More than
twenty years ago, scientists
extracted stem cells from the
embryos of mice. These stem
cells are described as
embryonic. The other main
type of stem cells is described
as adult. Embryonic stem
cells and adult stem cells are
very different.
Embryonic stem cells can divide to make more stem cells.
They wait for a signal. Then they start producing specialized
cells. These specialized cells form the tissues, which in turn
form the organs. Parent cell Two daughter cells
