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Class Roadmap

I. Introduction to Zoology

A. What is an Animal?Animal life began in Precambrian seas with the evolution of multicellular forms that lived by eating other organisms. Early animals populated seas, fresh water, and eventually the land.

B. Three things we focus on:1. Structure2. Nutrition3. Life history define animals.

C. Structure, nutrition, and life history define animals.

1. Animals are multicellular, heterotrophic, and eukaryotes. In contrast to autotrophic nutrition of plants and algae, animals must take into their bodies preformed organic chemicals. Animals can do this by ingestion-eating other organisms or organic material that is decomposing

2. Animals lack cell walls that provide strong support in the bodies of plants and fungi. The multicellular bodies of animals are held together by structural proteins, the most abundant being collagen.

3. Also unique among animals are two types of tissues responsible for impulse conductions and movement: nervous tissue and muscle tissue.4. Most animals reproduce sexually, with the diploid stage usually dominating the cycle. ***See diagram on next slide

Cleavage Blastula Gastrulation Gastrula

Cell Cycle: G1, S, G2, and Mitosis

D. Did the animal kingdom evolve from a flagellated protist?• Most scientist agree that

the animal kingdom in monophyletic; animal lineages can be traced back to a common ancestor.

• Likely a a flagellated protist over 700 million years ago.

• Related to a choanoflagellate, which arose about a billion years ago.

Going From A single cell to Multicellular Organism

This is an example of Phylogenic Tree

As an A & P class will work from left to right throughout the 1st marking period• Do you see any

patterns?

IntroductionHow did we get here?

II. Chapter 8 A. Early Concepts: Preformation versus Epigenesisa. Mystery of development in the 17th and

18th centuries1. Naturalist-philosophers claimed that

young animals were preformed in eggs and that development was simply a matter of unfolding what was already there.

2. A 17th Century Dutch histologist thought he saw a preformed human infant in sperm in a microscope he made.

3. 1759 Embryologist Kasper Wolff

• Studied the development of a chick• No preformed individual, only undifferentiated granular material that became

arranged into layers.• This process was called epigenesis-a fertilized

egg contains the building materials for development.

• Unknown forces control these actions???

B. Hierarchy of Development Decisions • Course of

Differentiation: cytoplasmic location and induction

• Cell types that make up the body do not just “unfold”, but arise from conditions created in preceding stages.

C. Fertilization (1n) egg + (1n) sperm=(2n) zygote

• The initial event in development in sexual reproduction is fertilization, the union of male and female gametes to form a zygote.

• Recombinant of parental and maternal genes

• Parthenogenesis-development without fertilization (Example some fish and salamanders)

D. Cleavage and Early Development • During cleavage the embryo divides repeatedly to

convert the large cytoplasmic mass into a large cluster of small maneuverable cells called Blastomeres.

E. Cleavage and Early Development • No growth during this period, only

subdivisions of mass, which continues until somatic cell size is attained. Think of it a origami!!!!

• So, what are somatic cells?• At the end of cleavage 100s to 1000s of

cells

Look at the Diagram to see an example of a VEGETAL POLE AND ANIMAL POLE

• What is the role of the yolk?

• Do the cells at the poles divide at the same rate?

Cleavage and Early Development

F. What can we learn from Development?

• Developmental Biology is a growing field!!• How can a zygote, a single layer cell,

produce a multitude of body parts in an organism and how gene expressions proceeds.

• Search for commonalities among organisms.

II. An overview of Development Following CleavageA. Blastulation

• Cleavage subdivides the mass of zygote until a cluster of cells called a blastula is formed (looks like a hollow mass of cells).

• In most animals, the cells are arranged around a central fluid-filled cavity called a blastocoel.

• Formation of a blastula stage, with its one layer of germ cells, occurs in all multicellular animlas.

B. Gastrulation and Formation of Two Germ Layers

a. Gastrulation converts the spherical blastula into a more complex configuration and forms a second germ layer.– One side of the blastula bends inward in a

process called invagination, forming a new internal cavity. Picture pushing in a beach ball-the inward region forms a pouch.

– The internal pouch is the gut cavity called an archenteron or gastrocoel.

– The opening to the gut, where the inward bending began, is the blastopore.

Gastrulation and Formation of Two Germ Layers

C. The gastrula stage has two layers:a. An outer layer of cells surrounding the blastocoel,

called ectodermb. An inner layer of cells is called endoderm– The gut opens only at the blastopore it is called a

blind or incomplete gut. Animals with a blind gut must consume food completely digested, or the remains of the food egested through the mouth. Ex sea anemones and flatworms.

– Most animals have a complete gut with a second opening, the anus.

c. Formation of the Mesoderm, a Third layer

i. Multicellular animals (not sponges) proceed blastula to gastrula

• Two germ layers called DIPLOBLASTIC

• Three germ layers called TRIPLOBLASTIC

– The third layer is called mesoderm

C. Formation of the Coelom• Coelomates are animals

with a true coelom, a fluid filled body cavity completely lined by tissues derived from mesoderm.

• The inner and outer layers of tissue that surround the cavity connect dorsally and ventrally to form mesenteries that suspend the internal organs.

Animals can be divided into three body type:

1. Acoelomate

2. Pseudocoelomate

3. Coelomate

D. Protostome vs Deuterostome in Coelomates• Mollusks, annelids, arthropods and some other

phyla are collectively called protostomes. • Echinoderms and chordates are called

deuterostomes.

4 Fundamental differences between the two groups:

***** See Class Handout or next slide

• Which process Radial or Spiral Cleavage will develop identical twins?

Example: Identical twins

Mechanisms of Development• First Nuclear

Equivalence• What does this

diagram tell us?

Mechanisms of Development• Second Cytoplasmic

specification• What does this

diagram tell?

Mechanisms of Development• Third Embryonic

induction• What does this

diagram tell?

Chapter 9

Architectural Pattern of an Animal

• Bilateria – Bilateral symmetry (2 sided)• A bilateral animal has a dorsal (top) side

and a ventral (bottom) side, but also an anterior (head) end and a posterior (tail) end and a left and right side.

Hierarchical Organization of Animal Complexity• 5 grades of hierarchical organization (Table 9.1)

– subcellular/protoplasmic (protozoans)• unicellular animals• organelles perform various func.

– cellular (sponges)• aggregation of cells that are functionally differentiated• division of labor but not associated w/ specific func.

– cell-tissue (jellyfish)• aggregation of similar cells that perform common func. (epithelial,

etc.)– tissue-organ (flatworms)

• assemblage of +1 tissues perform highly specialized func. (heart, etc.)

– organ system • assemblage of organs work together

– skeletal, muscular, digestive, nervous, endocrine, immune, reproductive, excretory, circulatory, respiratory, integumentary

Body Symmetry• Symmetry = correspondence in size and shape

of parts on opposite sides of a median plane– spherical symmetry = any plane passing through

center divides a body into mirrored halves• round appearance, rare

– radial symmetry = parts of body are arranged concentrically around oral/aboral axis, +2 plane through oral/aboral axis results in mirrored halves• tubular appearance, no front or back, sessile or free floating• hydra, jellyfish, sea urchin, adult sea star (bilateral larvae)• biradial symmetry = 2 planes can pass through oral/aboral axis to

produce mirrored halves– comb jellies

• Radiata (Cnidaria, Ctenophora) – not monophyletic group, arose separately

Body Symmetry– bilateral symmetry = cut along sagittal plane

divides animal into 2 equal halves (left, right)• better adapted for directional mvmt• monophyletic group called Bilateria• associated w/ cephalization (differentiation of head)

– well-suited for sensing/responding to environment• terms associated w/ bilaterally symmetrical animals

– anterior = head end– posterior = tail end– dorsal = back side– ventral = belly side– medial = midline– lateral = sides

Body Symmetry– distal = far from middle of body– proximal = near middle of body– frontal plane = divides body into dorsal and ventral halves– sagittal plane = divides body into right and left sides– transverse plane (a.k.a. cross section) = divides body into

anterior and posterior ends– pectoral = chest region, area supported by forelegs– pelvic = hip region, area supported

by hind legs

Body Cavities and Germ Layers• Body cavity = internal space w/i body

– 2 cavities in most animals– sponges have no body cavity

• Metazoan development– zygote develops into blastula

• blastula = layer of cells surrounding blastocoel (fluid-filled cavity)– blastocoel has no opening

– blastula develops into gastrula• gastrula = 1 side of blastula forms depression,

which forms gastrocoel/archenteron (gut cavity) – opening to depression = blastopore

» blastopore develops into mouth or anus– lining of gut = endoderm, outer layer = ectoderm

– gastrocoel and blastocoel form 2 cavities– blastocoel forms mesoderm in some sp.

• derived from endoderm

Protostomes

Deuterostomes

Mesoderm formation

Mesoderm Formation• In protostomes (“first mouth”)

– Annelida/Arthropoda/Mollusca– mesoderm forms from endodermal

cells near blastopore that migrate to blastocoel– 3 body plans emerge after following initial mesoderm formation

• acoelomate = blastocoel fills w/ mesoderm cells, thus only gut cavity– tissue btwn ecto- and endodermis filled by parenchyma cells

which are spongy and func. in food transport, waste disposal• pseudocoelomate = mesoderm cells line outer edge of blastocoel,

thus 2 body cavities (pseudocoelom, gut cavity)– pseudo b/c mesoderm partially surrounds cavity

• schizocoelous = blastocoel fills w/ mesoderm cells to form band of tissue around gut, programmed cell death results in space w/i mesodermal band, thus 2 body cavities (true coelom, gut cavity)

Mesoderm Formation• In deuterostomes (“second mouth”)

– Echinodermata/Chordata/Hemichordata– mesoderm forms from endodermal cells

in central portion of gut lining that expand into blastocoel

– 1 body plan• enterocoelous = mesodermal cells

expand outward to line blastocoel, thus 2 body cavities (true coelom, gut cavity)

– result similar to schizocoelous plan– cavities bound by mesoderm, lined w/ peritoneum

» peritoneum = thin membrane derived from mesoderm that lines coelom

» mesenteries = suspend organs in coelom

Developmental Patterns• Simplest developmental pattern (i.e. sponges)

– no distinct cleavage pattern– embryos develop to blastula stage only – blastula consists of 1 germ layer that reorganizes to form sponge

• aggregation of cells• Diploblastic developmental pattern (i.e. sea anemones)

– blastula develops into gastrula– develop 2 germ layers (ectoderm, endoderm)– develops tissues– typically radially symmetrical

• Triploblastic developmental pattern – develops 3rd germ layer (ectoderm, endoderm, mesoderm)– develops tissues– typically bilaterally symmetrical– blastula undergoes radial or spiral cleavage

Developmental Patterns• Radial cleavage accompanied by following to become

deuterstomes (frogs, sea urchins)– blastopore becomes anus– coelom forms by enterocoely– regulative cleavage of cytoplasm

• each blastomere (early cleavage cell) develops into normal larvae• Spiral cleavage accompanied by following to become

protostomes (snails, segmented worms)– blastopore becomes mouth– mesoderm forms from 4d cell in embryo

• thus acoelomate, pseudocoelomate or coelomate– mosiac cleavage of cytoplasm

• not all blastomeres develop into normal larvae– lophotrochozoan (molluscs, annelids) vs. ecdysozoan protostomes

(arthropods, nematodes)

No cleavage pattern Protostome

Deuterostome

Gastrula formation

No gastrula formation

Acoelomate

Dip

lobl

astic

Trip

lobl

astic

Radial cleavage

Spiral cleavage

Pseudocoelomate

Schizocoelomate

Enterocoelomate

Lophotrochozoan protostome

Ancestral unicellular organism

Unicellular Multicellular

Aggregation of cells Eumetazoan

BilateralRadial

Acoelomate

Pseudocoelomate

Schizocoelomate Enterocoelomate

Body Plans of Major Taxa

• Unicellularity vs. multicellularity– body forms diversify w/ advent of multicellular organisms

• Protozoans vs. mesozoans vs. metazoans• Eumetazoans vary in symmetry, # body layers, gut structure

– some have blind/incomplete gut (1 opening)– most have complete gut (entrance + exit) (tube w/i tube)– some segmented (repitition of similar body segments along long.

axis)• segment = metamere or somite• ↑ mobility and structural complexity