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CELL DIFFERENTIATION
Cell differentiation: The process by which an
undifferentiated cell reaches its specialized
function. It occurs during histogenesis.
Cell differentiation is stable.
Most differentiated cells cannot transform
into other cell types (it can happen during
regeneration).
As cell division proceeds, the cells not only
increase in number but also undergo
differentiation becoming specialized in
structure and function.
In the development of most multicellular
organisms, a single cell (fertilized egg) gives
rise to many different types of cells, each
with a different structure and
corresponding function.
CHARACTERISTICS OF CELL
DIFFERENTIATION
There are four characteristics of cell
differentiation.
They are:
1. It is stable phenomenon
2. It is induced by specific stimuli
3. It precede morphological difference
4. It is controlled by genetic factors
1. It is stable phenomenon
• One of the principle characteristics of cell differentiation in higher cells is
that once established, the differentiated state is very stable and can
persist throughout many cell generations. For example, a neuron will
persist as such throughout the lifetime of an individual.
2. It is induced by specific stimuli
• Another important characteristic of cell differentiation is that it is induced
in the organism by various stimuli but once it has been established, it can
persist even in the absence of the initial stimulus.
For example, differentiated cloned cell lines, such as steroid-secreting cell
lines are able to grow indefinitely in vitro. The differentiated state is
maintained over many cell generations.
3. It precede morphological difference
• In many cases before morphological difference
appears, the cell is committed to a particular
change due to cell differentiation process.
4. It is controlled by genetic factors
• Genes (genetic factors) enacted crucial role in
controlling and executing cell differentiation
process.
Key Concept
• As multicellular
organisms develop, their
cells differentiate (change
& separate) and form
levels of organization
• Why it Matters: so
Humans (we are
multicellular) can have
different kinds of cells,
tissues, organs, and organ
systems
Cells
• Are the simplest form of life
• Chemical elements organized into cells become living
matter.
• All organisms are made-up of cells
• All the substances of an organism are
the products of its cells.
• The number of cells from any organism ranges from
one to trillions.
• However, even the most complex organisms have a
relatively small (~200) catalog of differentiated cell
types with specialized function (bone, muscle, nerve).
Life is Cellular
–
–
Some things are only
one cell
(unicellular)
Some have many
cells (multicellular)
Unicellular Organisms may be
Prokaryotic
Eukaryotic
Unicellular Organisms
• “uni-” = one
• Prokaryotes are unicellular organisms
• Some algae, some protists, and some eukaryotes
(yeasts), are unicellular
• Can still do everything they need to stay alive
• Benefits over multicellular organisms:
– Need fewer resources
– Can live in harsher conditions
Multicellular Organisms
• “multi-” = more than one
• Plants, animals, some protists, and most fungi are
multicellular
• Start as a single cell  many cells  cells
differentiate (change) into different types of cells 
cells group together
•The fertilized egg gives rise
to a large number of cells
through cell division, but the
process of cell division alone
could only lead to increasing
numbers of identical cells.
Multicellular organisms depend on
interactions among different cell types.
CELL
TISSUE
stem
shoot system
leaf
vascular
tissue
ORGAN
lateral
roots
primary
root
root system
• Tissues are groups of cells that perform
a similar function.
• Organs are groups of tissues that
perform a specific or related function.
• Organ systems are groups of organs
that carry out similar functions.
SYSTEMS
•Nearly all of the cells of a multicellular organism
have exactly the same chromosomes and DNA.
•During the process of differentiation, only specific
parts of the DNA are activated; the parts of the DNA
that are activated determine the function and
specialized structure of a cell.
Specialized cells perform specific
functions.
• Cells develop into their mature forms through the process
of cell differentiation.
• Cells differ because different combinations of genes are
expressed.
• A cell’s location in an embryo helps determine how it will
differentiate.
Outer: skin cells
Middle: bone cells
Inner: intestines
Levels of Organization
•
•
•
•
1st Level: Cells
2nd Level: Tissues
3rd Level: Organs
4th Level: Organ Systems
• Cells  Tissues  Organs  Organ Systems
Level 1 : Cells
• Cells can be specialized (have a
certain function)
• Function = job
• Function is related to the cell
structure
• Structure = how parts of the cell
are put together
– Shape
– Material it’s made from
• Structure of a brain cell is
different from muscle cell
Cells Continued
• Cells occur in many
different shapes and
sizes so they can
perform many
different functions.
Level 2: Tissues
• Tissue = group of cells that work together to do a
specific job
• Ex: Heart muscle tissue
is made of heart muscle
cells
• Animals have 4 types of
tissue: nerve, muscle,
connective, protective
• Plants have 3 types of
tissue : transport, protective, ground
Level 3: Organs
• Organ = structure that is made up of 2 or more tissues
working together to get a specific job done
• Ex: Stomach – muscle tissue moves food, special tissues
make chemicals to digest food, connective tissue holds
stomach together, nervous tissue sends messages back
and forth between the stomach and brain
Level 4: Organ Systems
• Organ system = group of organs working
together to perform a specific function
• Each organ system has a specific job
• Ex: Digestive system is made of several organs
including the stomach and intestines
Structure of Animals
Cells
-basic unit of an animal’s structure
-become specialized
_______________________________
Tissues
-made of cells that work together to perform a specific function
__________________________________________
Organs
-made of different types of tissues that work together to perform a specific function
____________________________________________________
Organ Systems
-made of organs that work together to perform a specific function
_____________________________________________________________
Organisms
•The various types of
cells (such as blood,
muscle, or epithelial
cells) arrange into
tissues which are
organized into organs,
and, ultimately, into
organ systems.