Multicellular Organisms
Life Science Unit 1 lesson 11
Attendance link: http://goo.gl/forms/5BYhAfrua6
Expectations
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Required Class Connects
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Tuesday, Wednesday, & Thursday
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1:30-2:30 pm
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Be active and participate in class.
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Be respectful to your classmates
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Be positive in the chat box and use it correctly.
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Have a working microphone!
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You will need it during the lessons and break out
rooms.
If you have a question, please place it in the chat
box and repost it if I don’t see it.
Objectives
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Recognize that many organisms are
multicellular, and describe their
advantages.
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Explain that cells within a
multicellular organism differentiate
as the organism develops.
Evolution of Eukaryotes
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As early as 1.5 Bya eukaryotic cells appear as fossils
Figure 01A: Microfossils of
probable eukaryotic cells
Figure 01B: Microfossils of
probable eukaryotic cells
Reproduced from Schopf, J.W., Scientific American 239 (1978): 111-138.
Courtesy of J. William Schopf, Professor of Paleobiology & Director of IGPP
CSEOL
Figure 01C: Microfossils of
probable eukaryotic cells
Evolution of Eukaryotes
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Grypania spiralis has
been found in ancient
rocks in Michigan
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This fossil species is
preserved because it
formed simple shells
dinoflagellates
brown algae
water molds
Plasmodium falciparum
diatoms
foraminiferans
Figure B03: Diversity of forms of
foraminiferans
Reproduced from E. Haeckel. Art Forms in Nature. New York: Dover Publications, Inc., 1974 .
radiolarians
choanoflagellates
animals
amoeba
cellular slime mold
fungi
plasmodial slime mold
Which kingdoms do ALL
multicellular organisms belong to?
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Think about the type of multicellular organisms that you
know of.
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They are fall under the Domain of Eukarya.
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There are three Kingdoms that they fall into:
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Animalia
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Plantae
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Fungi
NOTE: In the OLS when asked for which kingdoms all
multicellular they what you to mark Animalia & Plantae.
Multicellular organisms
In a single-celled organism, all the
functions necessary for life must
be carried out in one cell.
In multicellular organisms, cells
specialize to perform different tasks.
This is one advantage of being
multicellular.
Cells that have adapted to a specific function are known
as specialized cells.
Specialized cells are grouped into tissues, which combine
to make organs and organ systems.
Disadvantages of being
multicellular.
 Because
they can be larger
they need more energy/food.
 Need
structural support like a
skeleton
 Cells
depend on each other so
if one cell malfunctions it
affects other cells.
Why specialize?
Unlike unicellular organisms, multicellular organisms need
specialized cells in order to survive.
In multicellular organisms, most cells are not in direct
contact with the environment. Therefore, specialized
cells, tissues and organs must:
 communicate between cells
 supply cells with nutrients
 control exchanges with
the environment.
Levels of Organization
 1st
Level: Cells
 2nd
Level: Tissues
 3rd
Level: Organs
 4th
Level: Organ Systems
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Cells  Tissues  Organs  Organ Systems
How are organisms organized?
Level 1 : Cells
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Cells can be specialized (have
a certain function)
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Function = job
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Function is related to the cell
structure
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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
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
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Level 3: Organs
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Organ = structure that is made up of 2 or more
tissues working together to get a specific job done
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Ex: Stomach – muscle tissue moves food, special tissues
make chemicals to digest food, connective tissue holds
stomach together, nervous tissue sends messages back and
Level 4: Organ Systems
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Organ system = group of organs working
together to perform a specific function
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Each organ system has a specific job
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Ex: Digestive system is made of several organs
including the stomach and intestines
What makes an organism?
What are stem cells?
All multicellular organisms
begin as a single cell. These
first cells are called stem cells.
These are unspecialized cells
capable of developing into
many different types of cell.
Stem cells found in embryos are
called embryonic stem cells
and develop into all the different
types of cell in the body.
In the earliest stages of
development, stem cells
simply divide to produce
more stem cells.
Changing cells
When the embryo contains about 500 cells, the cells stop
being the same and they start getting biger with each division.
They start to differentiate into different types of cell.
At this point, stem cells no longer form two new stem cells
when they divide. Instead, one of the two daughter cells
becomes a tissue cell.
stem cell
tissue cell
stem cell
Becoming specialized
Tissue cells continue to
divide and differentiate,
each time becoming more
and more specialized.
stem cell
tissue cells
Some will
become nerve
cells, others will
become blood
cells, muscle
cells, bone cells,
etc.
nerve cells
red blood
cells
cardiac muscle
cells
How tissues work together
Epithelial tissue forms a protective
covering for different parts of the body.
Glandular tissue secretes important
substances, such as hormones.
Muscular tissue contracts to
cause movement.
These tissues are all present in the small intestine.
Epithelial tissue forms the intestinal walls. Glandular
tissue secretes mucus to protect the epithelium from
digestive enzymes. Muscular tissue contracts to move
digested food along its tract.
Questions?
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Make sure you complete the assessments
in the OLS
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Part 1 Online has 5 questions
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Part 2 Offline has 2 questions
Make sure you save the whiteboard if you
need it
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File, save, whiteboard, All pages, & save as a
PDF file.
If you have any questions, please let me
know.