Animals AP Biology - Chapter 32

What is an Animal? Eukaryotic No cell wall Heterotrophic Bodies held together by collagen, tight junctions desmosomes and gap junctions (proteins) Heterotrophic Ingest then digest All reproduce sexually some also reproduce asexually

Reproduction and Development Sexual Diploid stage is dominant Small sperm fertilizes larger, nonmotile egg. This makes a diploid zygote

Development Zygote undergoes cleavage Succession of mitotic cell divisions without cell growth in between the divisions.

Development Cleavage leads to the formation of a blastula Hollow ball of cells

Frog Blastula and Future Embryonic Tissue Layers

Development The blastula then turns itself “inside out” to form the gastrula This process is known as gastrulation; frog1; frog 2; frog 3 This process produces the layers of embryonic tissues that will develop into the adult body parts.

Gastrulation Bastocoel – cavity in the blastula that provides space for gastrulation to occur Archenteron – the future gut cavity; forms during gastrulation Blastocoel gets smaller as gastrulation takes place.

Larvae Some animals develop directly into adults Other animals must pass through a larval stage Sexually immature form of an animal that is morphologically distinct from the adult Eats different food Different habitat Tadpole > frog metamorphosis

History of Animals Diversification began more than 1 billion years ago Common ancestor of the animals may have resembled modern choanoflagellates Protist that is the closest living relative of animals Colonial, flagellated protist

One hypothesis… …for origin of animals from flagellated protist..(the arrows represent evolutionary time).

Animal Body Plans Features of Body Plans Symmetry Tissues Body Cavities Protostome vs. Deuterostome development Body plans allow us to talk about levels of complexity

Symmetry Asymmetry – no symmetry - sponge

Symmetry Radial symmetry “Flower pot” Top and bottom (oral and aboral) No left/right; no head/tail

Symmetry Bilateral Symmetry Dorsal / ventral Left / right Anterior / posterior Sensory equipment concentrated at head end and central nervous system Cephalization; more efficient way to encounter the world when you are moving through it (rather than having the world drift around you)

Tissues Tissue Collection of cells that are similar in structure and work together to carry out a common function

Tissues Some animals lack tissues Sponges really just an aggregate of individual cells Individual cells function nearly independently, though not entirely independent

Tissues In animals with tissues the embryo becomes layered through gastrulation Embryonic Layers = germ layers These will form the various organs/tissues of the body The germ layers include Ectoderm Endoderm Mesoderm

Embryonic Tissue (Germ) Layers Diploblastic An animal that has only two germ layers Ectoderm, Endoderm Jellyfish/coral (phylum cnidaria) Triploblastic An animal that has three germ layers Ectoderm, Endoderm, and Mesoderm all animals higher than the jellyfish/coral

Embryonic Tissue Layers – Germ Layers Ectoderm Covers the surface of the embryo Gives rise to Outer covering CNS Endoderm Innermost germ layer Lines the gut Gives rise to organs like liver, lungs Mesoderm Between the ecto and endoerm Forms muscles and most organs that lie between the digestive tract and outer covering

Body Cavities Body cavity COELOM Fluid-filled space that separates the digestive tract from the outer body wall The space in which you find all the body’s internal organs Functions Fluid cushions suspended organs Hydrostatic skeleton in soft bodied animals (worms) Organs move independently of outer surface Some animals lack a coelom totally, some have a true coelom and some have a “sort of” coelom.

Body Cavities Acoelomate Animals Lack a body cavity They HAVE a gut space for food, but NOT a hollow space that contains the organs “solid body” flatworms

Body Cavities Pseodocoelomate Animals Have a space that contains the body organs, but it is not lined totally with mesoderm Thus it is not defined as a “true” coelom Round worms Hydrostatic skeleton

Body Cavities Coelomate animals Possess a True Coelom Cavity that is completely lined with mesoderm Contains fluid and the body organs Segmented worms and higher

Protostome vs. Deuterostome Development Distinguished by 3 features Cleavage pattern Coelom formation Fate of the blastopore

Protostome vs. Deuterostome Protosome Spiral cleavage Determinate cleavage Each embryonic cell’s fate is rigidly cast Deuterostome Radial cleavage Indeterminate cleavage If separated, each embryonic cell retains the ability to become a new embryo Makes identical twins possible Makes embryonic stem cells of high interest to researchers

Protostome vs. Deuterostome Coelom formation See diagram

Protstome vs. Deuterostome Fate of Blastopore Blastopore Indentation that leads to the formation of the archenteron during gastrulation After gastrulation a second opening forms at the opposite end of the gastrula Ultimately the blastopore and the second opening become the two openings of the digestive tube Mouth / anus

Protostome vs. Deuterostome In a protostome The blastopore becomes the MOUTH Segmented worms, mollucscs and arthropods

Protostome vs. Deuterostome In a deuterostome The blastopore becomes the ANUS Echinoderms and chordates

Animal Phylogenetic Tree About 35 animal phyla are recognized Relationships between them are debated Points in agreement: All animals share a common ancestor Sponges are basal animals (and the phylum is paraphyletic) Eumetazoa is a group of animals with true tissues The cnidarians are basal Most animal phyla belong to the clade bilateralia Vertebrate and some others belong to the clade deuterostomia

Embryonic Development

Embryonic Development

Embryonic Development

Choanoflagellate

Animal Origins

Symmetry