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Multicellular Life
Key concept: Cells work
together to carry out complex
*Multicellular organisms depend on
interactions among different cell types.*
*Multicellular organisms depend on
interactions among different cell types.*
shoot system
root system
*Specialized cells perform
specific functions.*
It is easy to see that a skin cell can divide to
make a new skin cell, but how does a complex
organism like you develop?
Your body begins as a single fertilized egg, if the
egg simply divided to make lots of identical cells
it would not form a baby.
To form intricate structures that make up your
body, cells must be specialized.
Specialized cells perform specific functions.
Cells develop into their mature forms and functions through
the process of cell differentiation.
Cells differ because different combinations of genes are
 Every cell in your body has a full set of DNA but each type
of cell uses only the specific genes it needs to carry out its
function- like a cookbook!
A cell’s location in an embryo helps determine how it will
Outer: skin cells
Middle: bone cells
Inner: intestines
A cell’s location in an embryo helps determine how it
will differentiate.
In animals, an egg undergoes many rapid divisions after it is
The resulting cells can migrate to a specific area, and the cells
quickly begin to differentiate.
The early animal embryo usually takes the shape of a hollow
ball. As the embryo develops, part of the ball folds inward,
forming an inner layer and creating an opening in the outer
cell layer. A middle layer of cells then forms between the two.
Outer: skin cells
Middle: bone
Inner: intestines
A cell’s location in an embryo helps determine how it
will differentiate.
As shown in the figures, the outer cell layer
differentiates to form the outer layer of skin
and elements of the nervous system such
as the spinal cord and brain.
The middle cell layer forms bones, muscles,
kidneys, and the inner layer of skin
The inner cell layer forms internal organs
such as the pancreas, lungs, and digestive
Outer: skin cells
Middle: bone cells
Inner: intestines
What are stem cells, and why are they
Stem cells have the ability to
divide and renew themselves
remain undifferentiated in form
develop into a variety of specialized cell types
When a stem cell divides, it forms either 2
stem cells or 1 stem cell + 1 specialized cell.
Stem cells are classified into three types.
– totipotent, or growing into any other cell type
– pluripotent, or growing into any cell type but a totipotent
– multipotent, or growing into cells of a closely related cell
Stem cells come from adults and embryos.
Embryonic stem cells
as their name suggests, are derived from embryos.
 Most embryonic stem cells are derived from embryos
that develop from eggs that have been fertilized by the
in vitro process with the consent of the donors.
 They are not derived from eggs fertilized in a woman's
 can be grown indefinitely in culture
 Can turn into almost any type of
Cell, so it is preferred over adult
stem cells
The use of embryonic stem
cells raises ethical issues
First, an egg is fertilized by a sperm cell in a petri dish.
The egg divides, forming an inner cell mass. These
cells are then removed and grown with nutrients.
Scientists try to control how the cells specialize by
adding or removing certain molecules.
Stem cells come from adults and embryos.
– Adult stem cells
– The primary role in a living organism is to maintain and repair the
tissue in which they are found.
– Where are adult stem cells found, and what do they normally
– Adult stem cells have been identified in many organs and tissues,
including brain, bone marrow, skeletal muscle, skin, teeth, heart,
gut and liver.
– They are thought to reside in a specific area of each tissue
(called a "stem cell niche").
– Stem cells may remain quiescent (non-dividing) for long periods
of time until they are activated by a normal need for more cells
to maintain tissues, or by disease or tissue injury.
– Typically, there is a very small number of stem cells in each
tissue, and once removed from the body, their capacity to divide
is limited, making generation of large quantities of stem cells
Adult stem cells continued…
– Scientists in many laboratories are trying to find
better ways to grow large quantities of adult stem
cells in cell culture and to manipulate them to
generate specific cell types so they can be used to
treat injury or disease.
– Some examples of potential treatments include
regenerating bone using cells derived from bone
marrow, developing insulin-producing cells for type 1
diabetes, and repairing damaged heart muscle
following a heart attack with cardiac muscle cells.
Adult stem cell differentiation
Stem Cell developments
UK, Japan scientists have discovered ways to
create tissues that would act like embryonic cells,
without the need to collect the cells from
Cells grown by the same scientists above are
thought to be linked to possibly killing cancer and
other major diseases.
A new method for generating brain cells from
urine samples is in the development stages.
Skin like cells in the urine can be reprogrammed, via a
pluripotent state, into neurons, glia, liver cells and heart
Funding Stem Cell Research
The U.S. Federal Court of Appeals has
overturned an August 2010 ban on federal
funding of embryonic stem cell research .
The ruling has been welcomed by the
Obama Administration.
 Private funding is also available through
programs, universities, companies, etc…