ASIM'S WEBWORLD View: Main School Main AP Biology Chapter Guides RELATED LINKS Review Questions and Answers		AP BIOLOGY: Chapter Thirty-Eight Outline THE GREAT DIVERSITY OF ANIMALS RESULTS FROM A LONG EVOLUTIONARY HISTORY Key Evolutionary Innovations Have Occurred in the Animals Progressive nature of animal evolution Key elements of body architecture fig 38.1 Body Plan Results from Gene Programmed Development SOME GENERAL FEATURES OF ANIMALS All Animals Are Heterotrophs Depend on photosynthetic organisms directly or indirectly Most are able to move from place to place in search of food Ingestion of food is followed by digestion within an internal cavity All Animals Are Multicellular Unicellular heterotrophs, "Protozoa," are Protists At least ten million species are currently alive Most animals are invertebrates Only 1% of all species are vertebrates Animals are diverse in form and include 35 phyla Size ranges from microscopic forms to enormous whales Most are marine, some are freshwater, few are terrestrial Arthropods, mollusks and chordates dominate the land Animals Constructed in a Common Manner Lack cell walls and are relatively flexible Cells are generally organized into tissues, except for sponges Are capable of movement Directly related to flexibility of cells Flying is the most specialized form of locomotion Most reproduce sexually Nonmotile eggs are much larger than motile sperm Cells formed by meiosis function directly as gametes There is no animal counterpart to plant gametophyte or sporophyte Adults and young are generally diploid Gametes are the only haploid cells Zygote becomes an adult through process of embryonic development Zygote divides mitotically forming a hollow ball of cells, a blastula This ball folds inward to form a hollow sac, a gastrula Opening of sac called the blastopore Cells subsequently grow and move in relation to one another Details differ from one phylum to another, but provide clues regarding their evolutionary relationships ANIMALS WITHOUT TISSUES: SPONGES Sponges Are the Simplest of Animals Lack definite symmetry Cells not organized into tissues fig 38.2 Body is little more than a mass of specialized cells Cells exhibit cell recognition Key property of animal cells Sponge passed through mesh will reaggregate General Biology of Sponges Adults are anchored to sea floor fig 38.3 Functions as water-filtering machine Body is vase shaped, perforated by tiny holes Choanocytes: specialized flagellated cells that line internal cavity Water forced through passageways by beating flagella Food particles in water trapped and ingested Choanocytes structurally resembles choanoflagellates Protist with a single flagellum Likely ancestor of sponges ADVENT OF TISSUE LEADS TO GREATER SPECIALIZATION: CNIDARIANS Animals Other than Sponges are Eumetazoans Possess definite symmetry Form three distinct cell layers Outer ectoderm, inner endoderm, intermediate mesoderm Layers give rise to tissues of adult body Ectoderm forms coverings of body and nervous system Mesoderm forms skeleton and muscles Endoderm forms digestive organs and intestines Most Primitive Eumetazoans Are Radially Symmetrical Body parts arranged around a central axis Exemplified by two phyla Cnidaria: hydroids, jellyfish, sea anemones and corals fig 38.4 Ctenophora: comb jellies fig 38.5 All other eumetazoans are fundamentally bilaterally symmetrical Echinoderm adults radially symmetrical, larvae bilaterally symmetrical General Biology of Cnidarians Carnivores, capture food with tentacles that surround mouth Possess cnidocytes: specialized structures located on tentacles Exhibit two body forms Polyp: cylindrical, generally attached to a substrate Medusa: umbrella-shaped, free floating, gelatinous Evolutionary innovation: extracellular digestion of food Sponge choanocyte or amoeboid cell takes food particle directly into itself Cnidarians digest food outside of cells in a gut cavity Same strategy pursued by fungi, but process occurs outside of body Innovation retained by all other advanced groups of animals Animals then able to digest something larger than its own cells BILATERAL SYMMETRY: SOLID WORMS Comparison of Bilateral Symmetry to Radial Symmetry fig 38.6 Bilateral symmetry found in all higher forms Bilateral organisms exhibit right and left halves, mirror images to each other Allows for differential adaptation of various parts of body Evolution of cephalization Move through environment headfirst Evolved various sensory organs generally grouped at head end More efficient in seeking food and avoiding predators fig 38.7 Simplest Bilaterally Symmetrical Animals Are the Solid Worms Largest phylum is Platyhelminthes, includes flatworms fig 38.8 Simplest phylum in which organs occur Organ: collection of different tissues that function as one unit Example: reproductive organs, testes and uterus General biology Dorsoventrally flattened bodies Bodies are solid, gut is the only internal cavity Body construction is acoelomate, without a body cavity fig 38.9 Bodies must be thin to allow diffusion of gases and nutrients Digestive system is branched with a single opening Most species are parasitic THE ADVENT OF A BODY CAVITY: ROUNDWORMS All Other Bilaterally Symmetrical Animals Possess a Body Cavity fig 38.10 Importance of the evolution of a body cavity Circulation: Fluids moving within cavity function as a circulatory system Movement: fluid in cavity makes body rigid Organ function: organs can function without being deformed Food movement not controlled by locomotion of animal Digestion and waste removal more efficient Pseudocoelomate Animals fig 38.9 Include seven phyla Body cavity, pseudocoel, located between endoderm and mesoderm Have complete, one-way digestive tracts Nematoda contains the most members, most are microscopic fig 38.11 BUILDING A BETTER BODY CAVITY: MOLLUSKS Coelomates Constitute the Bulk of the Animal Kingdom Coelom body cavity develops entirely within mesoderm fig 38.12 Supports various evolutionary relationships Acoelomates could give rise to coelomates or be derived from them Pseudocoelomate phyla could all have different origins Success of Coelomate Body Cavity Stems from Embryonic Development During primary induction primary tissues interact with each other Coelomate body plan allows necessary contact between mesoderm and endoderm Permits development of localized portions of digestive tract, i.e. stomach Mesoderm and endoderm separated by body cavity in psuedocoelomates Limits developmental interactions Coelom allows digestive tract to be longer than animal's body length Allows for storage of undigested food or food remnants: limits exposure to predators Longer exposure of food to enzymes improves digestion Tube-within-a-tube design allows for more flexibility and greater mobility Architecture of the coelomate animal Gut and internal organs suspended in coelom Coelom surrounded by epithelium layer, derived from mesoderm Parietal peritoneum lines outer wall Visceral peritoneum lines internal organs within cavity Internal body cavity provides space for expansion of gonads Allows for accumulation of eggs and sperm Advanced phyla able to evolve diverse reproductive strategies Large numbers of gametes stored and released under favorable conditions Requires development of sophisticated circulatory system Network of vessels carries fluid, blood, to all parts of body Blood carries nutrients and oxygen to tissues Removes wastes and carbon dioxide from tissues Circulation effected by contraction of muscular hearts Mollusks Are the Least Advanced Coelomates Only major coelomates without segmented bodies Second largest phylum of animals Second most successful land animals, next to insects More terrestrial mollusks than terrestrial vertebrates fig 38.13 Mollusk bodies composed of three segments: head, central visceral mass, foot Three classes: Gastropods, Bivalves, Cephalopods THE RISE OF SEGMENTATION: ANNELIDS Early Innovation in Coelomates Was Segmentation Body built from series of similar segments fig 38.14 Like prefabricated building Segmentation obvious in mesoderm early on Later reflected in endoderm and ectoderm Advantages to early embryonic segmentation Repetition of organ systems less lethal if one segment damaged Locomotion more effective when segments can move independently Offers evolutionary flexibility Small change in a segment can produce segment with new function Segments can be modified for various activities Segmentation First Evolved in Annelid Worms fig 38.15 Two-thirds are marine, rest are terrestrial Characterized by three principle features Repeated segments Visible as ring-like structures along body length Separated internally by partitions Each segment contains digestive, excretory and locomotor organs Fluid in segments creates hydrostatic skeleton that gives the segment rigidity Each segment can expand or contract independently Specialized segments Anterior segments modified with sensory organs Well-developed brain contained within one anterior segment Connections Provide ways for materials to pass between segments Circulatory system carries blood between segments Nerve cords connect ganglia in each segment Segmentation in Other Coelomates Present in arthropods and chordates, may not be obvious Many arthropod segments are fused Segments not apparent in human adults, visible in embryo Vertebrate muscles develop from repeated blocks called somites Vertebral column segmentation is more apparent INVENTION OF JOINTED APPENDAGES: ARTHROPODS Jointed Appendages Characteristic of the Most Successful Animal Phylum fig 38.16 Arthropod most certainly evolved from annelids fig 38.17 Arthropod segmentation not as evident as annelid segmentation Importance of jointed appendages verified in human skeletal joints Exoskeleton is a Limitation of the Arthropods Skeleton is rigid, made of chitin Muscles attach to the interior of the hard shell Provides protection, limits water loss Chitin cannot support great weight Exoskeleton must be thick to bear pull of muscles in large arthropods Extremely large arthropods are non-existent Strong flexible endoskeleton required to overcome limitation REDESIGNING THE EMBRYO: ECHINODERMS Coelomates Characterized into Two Groups by Embryology Protostomes Include mollusks, annelids, arthropods Mouth (stoma) develops from or near blastopore fig 38.18 Anus develops in another region of embryo Original state was characteristic of common ancestor of all eumetazoans Deuterostomes Includes echinoderms, chordates, few other related phyla Anus forms at or near blastopore fig 38.18 Mouth develops from another region of blastula Derived from protostome pattern of development Other Fundamental Differences Between Deuterostomes and Protostomes Present two different cleavage patterns Protostomes exhibit spiral cleavage fig 38.18 New cell buds off at oblique angle Produces closely packed array of cells Deuterostomes exhibit radial cleavage Cells divide parallel to and at right angles to polar axis Produces loosely packed array of cells Differences in developmental fate of cells Protostome cell fate is fixed when that cell first appears Individual cells will not develop into complete animal if separated Chemicals controlling developmental signals are localized early Deuterostome cell fate is fixed later in development Daughter cells from early divisions are totally identical Cells from early stages can become complete individuals Differences in development of celom from mesoderm Occurs simply and directly in protostomes Cells move away from one another Coelomic cavity expands within mesoderm Complex development in deuterostomes Groups of cells move around forming new tissue associations Coelom produced from invagination of archenteron Deuterostomes clearly derived from protostomes early in their evolution Echinoderms Were the First Deuterostomes fig 38.19 Name "spiny skin" refers to hard endoskeleton just beneath delicate skin Endoskeleton composed of ossicles, calcium-rich plates Are totally encase in living skin when first formed Fuse forming hard shell in adults Include sea stars, sea urchins, sand dollars, sea cucumbers fig 38.20 Echinoderms exhibit secondary radial symmetry Are bilaterally symmetrical as larva Become radially symmetrical as adults Adults possess five-part body plan Lack a centralized brain or central nervous system Possess a unique water vascular system Hydraulic system to aid movement Central ring with five radial canals Ultimately controls contraction or extension of hollow tube feet IMPROVING THE SKELETON: CHORDATES Chordates Employ a Truly Internal Endoskeleton fig 38.21 Characterized by flexible rod along back of embryo Muscles attach to rod providing flexible locomotion Leads to possibility of truly large animals Three features characterize chordates Single dorsal hollow nerve cord Long, stiff rod-like notochord, beneath nerve cord Pharyngeal slits located behind mouth Features may not be apparent at all times Human possess three characteristics as embryos Adult humans retain nerve cord, one pair of slits becomes Eustachian tubes Chordate Body Plan Are deuterostomes, nearest relatives are echinoderms Are more or less segmented Many have jointed appendages Vertebrates Are Specialized Group of Chordates Tunicates and lancets are non-vertebrate chordates fig 38.22 Special characteristics of vertebrates Possess backbone Notochord surrounded and replaced by bony vertebral column Hollow tube of bones protecting dorsal nerve cord Exhibits distinct head, also called craniate chordates Vertebrate endoskeleton is made of bone fig 38.23 Special tissue containing collagen protein coated with calcium phosphate salt Bone is strong without being brittle, like chitin