Lecture 10 BIO 311D 1st Edition Outline of Last Lecture I Sympatric Speciation II Habitat Differentiation III Sexual selection IV Phylogeny V Hierarchal Classification VI Homology and Analogy Differences Outline of Current Lecture I Cell Structure and Specialization II Reproduction and Development III Body Plans IV Tissues V Protostome and Deuterostome Developments Current Lecture 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 Plants have cell walls animals do not So we have collagen in replacement Animals have specialized cells such as nervous tissues and muscle tissues Blastula is hallow inside cells are formed on the outside Yellow section turns into digestive tract Outer layered cells are called the ectoderm Inner most cells are the endoderm Middle layer is mesoderm Why should animals with radial symmetry be better able to do than those with bilateral symmetry A Move quickly in one direction B Detect threats from above or below equally well C Deal effectively with food distributed homogeneously in 360 degrees D Focused attention in a single direction 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 Difference is whether or not they have larva immature animals that cannot reproduce or not Humans are different in that they do not have larva Humans are similar to other animals such that they have Hox genes 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 Most animals and only animals have Hox genes that regulate the development of body form Although the Hox family of genes has been highly conserved it can produce a wide diversity of animal morphology Body Plans Animals can be characterized by body plans Zoologists sometimes categorize animals according to a body plan a set of morphological and developmental traits Some developmental characteristics are conservative For example the molecular control of gastrulation is conserved among diverse animal groups 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 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 Radial animals are often sessile or planktonic drifting or weakly swimming Bilateral animals often move actively and have a central nervous system Advantages of body cavities Specialization Absorption of vibrations such as the heart to avoid the whole body from moving Tissues 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 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 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 Coelomates and pseudocoelomates belong to the same grade A grade is a group whose members share key biological features A grade is not necessarily a clade an ancestor and all of its descendants Protostome and Deuterostome Developments Based on early development many animals can be categorized as having protostome development or deuterostome development 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 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 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 Zoologists recognize about three dozen animal phyla Phylogenies now combine morphological molecular and fossil data Current debate in animal systematics has led to the development of multiple hypotheses about the relationships among animal groups Protostome and deuterostome development are distinguished by differences in A Cleavage coelom formation and the fate of the blastopore B Cleavage the fate of the blastopore and radial symmetry C Gastrulation radial symmetry and diploblastic animals D Triploblastic animals bilateral symmetry and indeterminate cleavage What is true of modern animal phylogenies A They take no account of an animals body plan B They portray an animals place on the scale of nature scala naturae C They rely solely on molecular genetic data D They are hypothetical
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