Animal Diversity (32) Animal Development (47) Concept 32.1:

Animal Diversity (32) Animal Development (47) Concept 32.1:

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 FER TI

Egg LIZ ATI O Adult frog N Zygote EA

L C Metamorphosis STR ULA TI NO GA IS OR NES GE Larval

stages GA GE A V Tail-bud embryo Blastula ON Gastrula

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 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 Ectoderm is the germ layer covering the embryos 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 (b) Coelom formation Radial and indeterminate 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

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