Transcript Animal Development

Animal Diversity (32)
Animal Development (47)
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
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
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
Figure 32.2-3
Zygote
Cleavage
Blastocoel
Cleavage
Eight-cell
stage
Blastula
Cross section
of blastula
Gastrulation
Blastocoel
Endoderm
Ectoderm
Archenteron
Cross section
of gastrula
Blastopore
• 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
Figure 47.2
EMBRYONIC DEVELOPMENT
Sperm
Zygote
Adult
frog
Egg
Metamorphosis
Blastula
Larval
stages
Gastrula
Tail-bud
embryo
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
Figure 47.3-5
Sperm
plasma
membrane
Sperm
nucleus
Basal body
(centriole)
Sperm
head
Acrosome
Jelly coat
Sperm-binding
receptors
Fertilization
envelope
Acrosomal
process
Actin
filament
Cortical
Fused
granule
plasma
membranes
Hydrolytic enzymes
Perivitelline
space
Vitelline layer
Egg plasma membrane
EGG CYTOPLASM
• 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
Figure 47.4
EXPERIMENT
10 sec after
fertilization
25 sec
35 sec
1 min
10 sec after
fertilization
20 sec
30 sec
500 m
RESULTS
1 sec before
fertilization
CONCLUSION
Point of sperm
nucleus
entry
Spreading
wave of Ca2
Fertilization
envelope
500 m
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
© 2011 Pearson Education, Inc.
Figure 47.6
50 m
(a) Fertilized egg
(b) Four-cell stage (c) Early blastula
(d) Later blastula
Figure 32.2-3
Zygote
Cleavage
Blastocoel
Cleavage
Eight-cell
stage
Blastula
Cross section
of blastula
Gastrulation
Blastocoel
Endoderm
Ectoderm
Archenteron
Cross section
of gastrula
Blastopore
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
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
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
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
RESULTS
1 Early stages of
development
100 m
Figure 32.6
2 32-cell stage
Site of
gastrulation
3 Early gastrula
stage
4 Embryos with
blocked -catenin
activity
Site of
gastrulation
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
Figure 32.7
(a) Radial symmetry
(b) Bilateral symmetry
• 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
Tissues (Gastrulation)
• Animal body plans also vary according to the
organization of the animal’s 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
• Ectoderm is the germ layer covering the embryo’s
surface
• Endoderm is the innermost germ layer and lines
the developing digestive tube, called the
archenteron
• 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
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
Figure 32.8
(a) Coelomate
Coelom
Digestive tract
(from endoderm)
Body covering
(from ectoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
(b) Pseudocoelomate
Body covering
(from ectoderm)
Pseudocoelom
Digestive tract
(from endoderm)
Muscle layer
(from
mesoderm)
(c) Acoelomate
Body covering
(from ectoderm) Tissuefilled region
(from
mesoderm)
Wall of digestive cavity
(from endoderm)
• A pseudocoelom is a body cavity derived from the
mesoderm and endoderm
• Triploblastic animals that possess a
pseudocoelom are called pseudocoelomates
• Triploblastic animals that lack a body cavity are
called acoelomates
Protostome and Deuterostome Development
• Based on early development, many animals can
be categorized as having protostome
development or deuterostome development
Figure 32.9
Protostome development
(examples: molluscs,
annelids)
(a) Cleavage
Deuterostome development
(examples: echinoderms,
chordates)
Eight-cell stage
Eight-cell stage
Spiral and determinate
Radial and indeterminate
(b) Coelom formation
Coelom
Archenteron
Coelom
Mesoderm
Blastopore
Blastopore
Solid masses of mesoderm
split and form coelom.
(c) Fate of the
blastopore
Mesoderm
Folds of archenteron
form coelom.
Anus
Mouth
Digestive tube
Key
Ectoderm
Mesoderm
Endoderm
Mouth
Mouth develops from blastopore.
Anus
Anus develops from blastopore.
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
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