Evolution of Multicellular Organisms

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Evolution of Multicellular Organisms
Multicellular Organization
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The story of how multicellular organisms evolved

• The earliest organisms were prokaryotes without
  nuclei (ex. bacteria) which relied on the
  environment for resources.
• They competed for limited resources. Those with
  adaptations survived better.
• One adaptation was having a nucleus and
  eukaryotes evolved!

WOW, THATS AWESOME!
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The story of multicellular organisms continued

• Certain eukaryotes began living together
  temporarily in groups. These cells specialized in
  performing certain functions and as a result
  gained benefits from being part of the group.
  These eukaryotes are called colonial organisms.
• Colonial organisms
• Middle ground between single celled
  multi-celled organisms
• Lack tissues and organs, but have cell
  specialization
• Ex. Volvox

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The story of multicellular organisms continued

• Its believed multicellular organisms evolved
  from colonial organisms that slowly became less
  able to live on their own because of more
  specialization, which lead to differentiation.
• Differentiation - taking on specific structures
  and carrying out specific functions
• Cell specialization- each cell performs a
  different function
• Ex. Nerve cells will transmit messages
• Skin cells will offer protection

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How are cells organized?

• In unicellular organisms one cell carries out
  all the functions of life.
• In multicellular organisms cells are
  specialized and rely on the other body cells for
  survival.
• Organization in multicellular organisms follows
  this pattern
• cells ? tissues ? organs? organ systems? organism

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cells ? tissues ? organs? organ systems? organism

• Groups of similar cells are organized into
  tissues that perform specific functions.
• When several tissues interact to perform a
  function, we call them Organs.
• Organ systems are groups of organs that work
  together to perform a task.
• All organ systems interact to make an organism.
  No one system could survive without the others