Biology 102 Chapter 43 Animal Development
1. List the functions of fertilization.
---forms a diploid zygote from haploid sets of chromosomes
from two individuals
---triggers onset of embryonic development
2. Describe the acrosomal reaction and explain how it ensures the
gametes are cospecific.
---is discharge of hydrolytic enzymes from vesicle in
acrosome of sperm cell
---enzymes enable acrosomal process to elongate and
penetrate jelly coat of egg
---protein coating tip of process attaches to specific
receptors on vitelline layer of egg (just external
to plasma membrane
---this provides species specificity for fertilization
3. Describe the cortical reaction.
---fusion of egg and sperm membranes stimulates series of
changes in egg’s cortex known as cortical reaction
---fusion of sperm and egg stimulates release of Ca2+ from
egg cell’s endoplasmic reticulum
--signaling pathway also leads to production of IP3
which opens ligand-gated calcium channels on ER
---high Ca2+ [] results in change in egg’s cortical
granules (special vesicles)
---increase in Ca2+ causes cortical granules to fuse with
plasma membrane and release contents into perivitelline
space outside plasma membrane
---contents of cortical granules include enzymes that
separate vitelline layer from plasma membrane
---osmosis causes perivitelline space to swell
---swelling elevates vitelline layer and other granule
enzymes harden it to form fertilization membrane
---this slow block to polyspermy consists of fertilization
membrane and other changes to egg’s surface
4. Explain how the acrosomal and cortical reactions function
sequentially to prevent polyspermy.
---acrosomal reaction causes sperm and egg’s plasma
membrane to fuse which allows the sperm nucleus to
enter the egg
--Na+ flows into egg cells & changes membrane potential
---this causes depolarization of plasma membrane that
prevents other sperm cells from uniting with egg
---this fast block to polyspermy operates until slow block
provided by cortical reaction can function
5. Describe the changes that occur in an activated egg.
---sharp rise in cytoplasmic Ca+ [] incites metabolic
changes that activates egg cell
---cellular respiration and protein synthesis rates >
---cytoplasmic pH changes from slightly acidic to
slightly alkaline due to H+ extrusion
---sperm nucleus within egg swells and merges with
egg nucleus to form zygote (actual fertilization)
---DNA replication begins & first division occurs in
about 90 minutes
6. Describe the process of gastrulation and explain its
importance.
---gastrulation involves an extensive rearrangement of
cells which transforms the blastula (hollow ball of
cells) into a three-layered embryo called the
gastrula
---set of common cellular changes is involved with all
animals
--changes in cell motility, shape, & cellular adhesion
to other cells and to molecules of extracellular
matrix
---some cells at or near surface move to more interior
location
---three layers produced by gastrulation are embryonic
tissues called embryonic germ layers
---these three cell layers (primary germ layers) will
eventually develop into all parts of adult animal
---ectoderm (outermost layer) develops into nervous
system and outer layer of skin in adult animals
---endoderm (lines the archenteron) develops into
lining of digestive tract and associated organs
(liver, pancreas)
---mesoderm (partly fills space between ectoderm and
endoderm) develops into kidneys, heart, muscles,
inner layer of skin, and most other organs
7. List adult structures derived from each of the primary tissue
layers.
---see #6 above
8. Using diagrams identify the various stages of embryonic
development of an amphibian.
---neural tube and notochord are first organs to develop
in frogs/other chordates
---dorsal mesoderm above archenteron condenses to form
notochord
---ectoderm above rudimentary notochord thickens to form
neural plate that sinks below embryo’s surface
--rolls into a neural tube which will become brain and
spinal cord
---notochord elongates and stretches embryo lengthwise
and functions as core around which mesoderm cells that
form vertebrae gather
---strips of mesoderm lateral to notochord condense into
blocks of mesodermal cells called somites from which
will develop vertebrae and muscles associated with
axial skeleton
---organogenesis continues as ectoderm gives rise to
epidermis, epidermal glands, inner ear, and eye lens
---mesoderm gives rise to notochord, coelom lining,
muscles, skeleton, gonads, kidneys, and most of
circulatory system
---endoderm forms digestive tract lining, liver, pancreas,
and lungs
---neural crest forms from ectodermal cells which develop
along border where neural tube breaks off from ectoderm
--these cells migrate and form pigment cells in skin,
some bones and muscles of skull, teeth, adrenal
medulla, and parts of peripheral nervous system
---end result is an aquatic, herbivorous tadpole
9. List and explain the functions of the extraembryonic
membranes.
---chorion forms from trophoblast and surrounds the embryo
and all extraembryonic membranes
---amnion forms as dome above the epiblast and encloses
embryo in fluid-filled cavity
---yolk sac encloses fluid-filled cavity but no yolk
--its membrane early site of blood cell formation
---allantois develops from outpocketing of rudimentary
gut and is incorporated into umbilical cord where it
forms blood vessels that transport oxygen and nutrients
from placenta to embryo and waste products from
embryo to placenta
10. Explain how interactions among the three primary tissue
layers influence organogenesis.
---various regions of 3 germ layers develop into the
rudiments of organs during organogenesis
---three kinds of morphogenetic changes, folds, splits,
and dense cluttering (condensation) are first evidence
of organ building
---see overhead
11. Describe the importance of cell location and orientation
along the three body axes with respect to polarity in the embryo,
morphogenetic movements, and pattern formation.
---morphogenesis is major aspect of development
--only in animals does it involve movement of cells
---movement of parts of cell can bring about changes in
in cell shape/enable cell to migrate in an embryo
---changes in both cell shape and position involved in
cleavage, gastrulation, and organogenesis
---bilaterally symmetrical animals have anteriorposterior axis, dorsal-ventral axis, and left and
right sides
---establishing basic body plan is first step in
morphogenesis
--prerequisite for development of tissues/organs
---in mammals, polarity does NOT seem to be determined
until after cleavage
--most other species, it is established earlier
---inductive signals play major role in pattern
formation; the development of animal’s spatial
organization
--arrangement of organs/tissues in their characteristic
places in three-dimensional space
---molecular cues controlling pattern formation (called
positional information) tell a cell where it is
with respect to the animal’s body axes and help
to determine how the cell and its descendents
respond to future molecular signals