What is an Animal

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What is an Animal?
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Characteristics of Animals

• Animals are eukaryotic, multicellular organisms
• Cells do not have cell walls
• Can move in some way
• All animals are heterotrophic must consume food
  (autotrophs like plants or other heterotrophs
  like hamburger from a cow) to obtain energy.
• Digest food
• Have specialized cells

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Development

• Animals share similar developmental stages.
• Fertilization Sperm (1N half the genetic
  material of the male adult) joins with the egg
  (1N half the genetic material of the female
  adult) The fertilized egg is called a zygote.
• Cell division The zygote divides through the
  process of cleavage. Once the cell division
  starts the name changes from zygote to embryo.
• The cells continue to divide until they form a
  hollow ball of cells called the blastula. The
  hollow space is called the blastocoel.
• The cells on one side of the blastula buckle
  inward to form the gastrula.

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Development continued

• The layer of cells on the outer surface of the
  gastrula make the ectoderm. This continues to
  grow and eventually becomes the skin and nervous
  system.
• The layer that folds in on the gastrula is called
  the endoderm. The endoderm continues to grow and
  the cells eventually differentiate into the
  digestive system and digestive organs.
• Some animals develop an additional layer between
  the ecto and endoderm. The cells come from the
  endoderm and the new middle layer is called the
  mesoderm. The mesoderm becomes the muscular,
  respiratory, circulatory, and excretory systems.

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Development continued

• From the gastrula on the cells continue to grow
  and differentiate into tissues, organs, and
  systems.
• If the opening (blastopore) formed by the
  invagination (buckling) of the gastrula becomes
  the mouth the animal is called a Protostome. EX.
  Earthworms, insects
• If the mouth of the animal develops from another
  area (not the opening, or blastopore) on the
  gastrula it is called a Deuterostome.

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Image taken from http//www.lander.edu/rsfox/310as
teriasLab_files/image010.jpg
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Image Taken from http//www.sci.muni.cz/ptacek/REP
RODUKCE2_soubory/image072.gif