Animal Diversity (32) Animal Development (47)

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Animal Diversity (32) Animal Development
(47)
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Concept 32.1 Animal are multicellular,
heterotrophic eukaryotes with tissues that
develop from embryonic layers

• There are exceptions to nearly every criterion
  for distinguishing animals from other life-forms
• Several characteristics, taken together,
  sufficiently define the group

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Cell Structure and Specialization

• Animals are multicellular eukaryotes
• Their cells lack cell walls
• Their bodies are held together by structural
  proteins such as collagen
• Nervous tissue and muscle tissue are unique,
  defining characteristics of animals
• Tissues are groups of cells that have a common
  structure, function, or both

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Reproduction and Development

• Most animals reproduce sexually, with the diploid
  stage usually dominating the life cycle
• After a sperm fertilizes an egg, the zygote
  undergoes rapid cell division called cleavage
• Cleavage leads to formation of a multicellular,
  hollow blastula
• The blastula undergoes gastrulation, forming a
  gastrula with different layers of embryonic
  tissues

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Figure 32.2-3
Zygote
Cleavage
Blastocoel
Cleavage
Gastrulation
Eight-cellstage
Cross sectionof blastula
Blastula
Blastocoel
Endoderm
Ectoderm
Archenteron
Cross sectionof gastrula
Blastopore
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• Many animals have at least one larval stage
• A larva is sexually immature and morphologically
  distinct from the adult it eventually undergoes
  metamorphosis
• A juvenile resembles an adult, but is not yet
  sexually mature

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Figure 47.2
EMBRYONIC DEVELOPMENT
Sperm
Zygote
Adultfrog
Egg
FERTILIZATION
CLEAVAGE
Metamorphosis
Blastula
GASTRULATION
ORGANO-GENESIS
Larvalstages
Gastrula
Tail-budembryo
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Fertilization

• Molecules and events at the egg surface play a
  crucial role in each step of fertilization
• Sperm penetrate the protective layer around the
  egg
• Receptors on the egg surface bind to molecules on
  the sperm surface
• Changes at the egg surface prevent polyspermy,
  the entry of multiple sperm nuclei into the egg

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Figure 47.3-5
Spermplasmamembrane
Spermnucleus
Fertilizationenvelope
Acrosomalprocess
Basal body(centriole)
Actinfilament
Spermhead
Corticalgranule
Fusedplasmamembranes
Acrosome
Hydrolytic enzymes
Perivitellinespace
Jelly coat
Vitelline layer
Sperm-bindingreceptors
EGG CYTOPLASM
Egg plasma membrane
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• Fusion of egg and sperm also initiates the
  cortical reaction
• Seconds after the sperm binds to the egg,
  vesicles just beneath the egg plasma membrane
  release their contents and form a fertilization
  envelope
• The fertilization envelope acts as the slow block
  to polyspermy

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Figure 47.4
EXPERIMENT
10 sec afterfertilization
25 sec
35 sec
1 min
500 ?m
RESULTS
1 sec beforefertilization
30 sec
20 sec
10 sec afterfertilization
500 ?m
CONCLUSION
Fertilizationenvelope
Spreadingwave of Ca2?
Point of spermnucleusentry
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Cleavage

• Fertilization is followed by cleavage, a period
  of rapid cell division without growth
• Cleavage partitions the cytoplasm of one large
  cell into many smaller cells called blastomeres
• The blastula is a ball of cells with a
  fluid-filled cavity called a blastocoel

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Figure 47.6
50 ?m
(a) Fertilized egg
(d) Later blastula
(b) Four-cell stage
(c) Early blastula
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Figure 32.2-3
Zygote
Cleavage
Blastocoel
Cleavage
Gastrulation
Eight-cellstage
Cross sectionof blastula
Blastula
Blastocoel
Endoderm
Ectoderm
Archenteron
Cross sectionof gastrula
Blastopore
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Concept 47.3 Cytoplasmic determinants and
inductive signals contribute to cell fate
specification

• Determination is the term used to describe the
  process by which a cell or group of cells becomes
  committed to a particular fate
• Differentiation refers to the resulting
  specialization in structure and function

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Axis Formation

• A body plan with bilateral symmetry is found
  across a range of animals
• This body plan exhibits asymmetry across the
  dorsal-ventral and anterior-posterior axes
• The right-left axis is largely symmetrical

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Cleavage

• In protostome development, cleavage is spiral and
  determinate
• In deuterostome development, cleavage is radial
  and indeterminate
• With indeterminate cleavage, each cell in the
  early stages of cleavage retains the capacity to
  develop into a complete embryo
• Indeterminate cleavage makes possible identical
  twins, and embryonic stem cells

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Concept 32.3 Animals can be characterized by
body plans

• Zoologists sometimes categorize animals according
  to a body plan, a set of morphological and
  developmental traits

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Figure 32.6
RESULTS
Early stages ofdevelopment
100 ?m
32-cell stage
Site of gastrulation
Early gastrulastage
Site of gastrulation
Embryos withblocked ?-cateninactivity
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Symmetry

• Animals can be categorized according to the
  symmetry of their bodies, or lack of it
• Some animals have radial symmetry, with no front
  and back, or left and right

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Figure 32.7
(a) Radial symmetry
(b) Bilateral symmetry
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• Two-sided symmetry is called bilateral symmetry
• Bilaterally symmetrical animals have
• A dorsal (top) side and a ventral (bottom) side
• A right and left side
• Anterior (head) and posterior (tail) ends
• Cephalization, the development of a head

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Tissues (Gastrulation)

• Animal body plans also vary according to the
  organization of the animals tissues
• Tissues are collections of specialized cells
  isolated from other tissues by membranous layers
• During development, three germ layers give rise
  to the tissues and organs of the animal embryo

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• Ectoderm is the germ layer covering the embryos
  surface
• Endoderm is the innermost germ layer and lines
  the developing digestive tube, called the
  archenteron

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• Sponges and a few other groups lack true tissues
• Diploblastic animals have ectoderm and endoderm
• These include cnidarians and comb jellies
• Triploblastic animals also have an intervening
  mesoderm layer these include all bilaterians
• These include flatworms, arthropods, vertebrates,
  and others

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Body Cavities

• Most triploblastic animals possess a body cavity
• A true body cavity is called a coelom and is
  derived from mesoderm
• Coelomates are animals that possess a true coelom

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Figure 32.8
(a) Coelomate
Coelom
Body covering(from ectoderm)
Tissue layerlining coelomand suspendinginternal
organs(from mesoderm)
Digestive tract(from endoderm)
(b) Pseudocoelomate
Body covering(from ectoderm)
Muscle layer(frommesoderm)
Pseudocoelom
Digestive tract(from endoderm)
(c) Acoelomate
Body covering(from ectoderm)
Tissue-filled region(frommesoderm)
Wall of digestive cavity(from endoderm)
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• A pseudocoelom is a body cavity derived from the
  mesoderm and endoderm
• Triploblastic animals that possess a pseudocoelom
  are called pseudocoelomates

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• Triploblastic animals that lack a body cavity are
  called acoelomates

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Protostome and Deuterostome Development

• Based on early development, many animals can be
  categorized as having protostome development or
  deuterostome development

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Figure 32.9
Protostome development(examples
molluscs,annelids)
Deuterostome development(examples
echinoderms,chordates)
(a) Cleavage
Eight-cell stage
Eight-cell stage
Spiral and determinate
Radial and indeterminate
(b) Coelom formation
Coelom
Archenteron
Coelom
Blastopore
Mesoderm
Blastopore
Mesoderm
Solid masses of mesodermsplit and form coelom.
Folds of archenteronform coelom.
Anus
Mouth
Digestive tube
Key
Ectoderm
Mouth
Anus
Mesoderm
Mouth develops from blastopore.
Anus develops from blastopore.
Endoderm
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Coelom Formation

• In protostome development, the splitting of solid
  masses of mesoderm forms the coelom
• In deuterostome development, the mesoderm buds
  from the wall of the archenteron to form the
  coelom

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Fate of the Blastopore

• The blastopore forms during gastrulation and
  connects the archenteron to the exterior of the
  gastrula
• In protostome development, the blastopore becomes
  the mouth
• In deuterostome development, the blastopore
  becomes the anus