Multicellular Life
Bio.1.1.3
Explain how instructions in DNA lead to cell
differentiation and result in cells specialized to
perform specific functions in multicellular
organisms.
Explain the process of cell differentiation as
the
basis for the hierarchical organization of organisms
(including cells, tissues, organs, and organ
systems).
Multicellular Life
•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.
•As cell division proceeds, the cells not only
increase in number but also undergo differentiation
becoming specialized in structure and function.
Multicellular Life
•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 Life
•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.
Multicellular Life
Multicellular organisms depend on interactions among
different cell types.
CELL
TISSUE
leaf
stem
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.
shoot system
SYSTEMS
Multicellular Life
•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.
Multicellular Life
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
Multicellular Life
•Because all cells contain the same DNA, all cells
initially have the potential to become any type of
cell.
•Once a cell differentiates, the process can not be
reversed.
•Stem cells are unspecialized cells that continually
reproduce themselves and have, under appropriate
conditions, the ability to differentiate into one or
more types of specialized cells.
Multicellular Life
Stem cells are unique body cells.
• Stem cells have the ability to
– divide and renew themselves
– remain undifferentiated in form
– develop into a variety of specialized cell types
Multicellular Life
• 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 cell
– multipotent, or growing into cells of a closely related cell
family
Multicellular Life
•Embryonic cells, which have not yet differentiated
into various cell types, are called embryonic stem
cells.
•Stem cells found in adult organisms, for instance in
bone marrow, are called adult stem cells.
•Scientists have recently demonstrated that stem
cells, both embryonic and adult, with the right
laboratory culture conditions, differentiate into
specialized cells.
Multicellular Life
• Stem cells come from adults and embryos.
– Adult stem cells can be hard to isolate and grow.
– The use of adult stem cells may prevent transplant
rejection.
– The use of embryonic
stem cells raises
ethical issues
– Embryonic stem cells
are pluripotent and
can be grown indefinitely
in culture.
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.
Multicellular Life
• The use of stem cells offers many currently realized and
potential benefits.
– Stem cells are used to treat leukemia and lymphoma.
– Stem cells may cure disease or replace damaged
organs.
– Stem cells may revolutionize the drug development
process.
Multicellular Life
HW:
•Discussion Board
•Project