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BIO153H5 (147)
Chapter 32

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Christoph Richter

Chapter 32 NotesAnimals are the only multicellular heterotrophs on the tree of life that ingest their food Fungi are multicellular heterotrophs but they absorb nutrientsSome slime moulds could also be classified as multicellular heterotrophs that ingest food but they are multicellular only during the dispersal phase of their life cycle they are unicellular when they feedAll animals move under their own power at some point in their life cycle and all animals other than sponges have1Specialized cells called neurons nerve cells that transmit electrical signals to other cells 2Muscle cells that can change the shape of the body by contractingAnts live in colonies that may include millions of individuals But colonymates cooperate so closely in feeding defence and rearing young that each ant seems like a cell in a multicellular organism instead of an individualSome ants live in trees and protect their host trees by attacking giraffes and other grazing animals a million times their size The trees provide oilrich growths that the ants eat Rancher ants protect the plantsucking insects called aphids from spiders and other predators and eat the sugarrich honeydew that aphids secrete from their anusFarmer ants eat fungi that they plant fertilize and harvest in underground gardensParasitic ants look and smell like a host ant species but enslave them forcing the hosts to rear the young of the parasitic species instead of their ownAnimals are key consumers in virtually every ecosystemfrom the deep oceans to alpine icefields and from tropical forests to arctic tundrasSuggest that there are between 10 million and 50 million animal species living todayEach animal phylum has distinct morphological featuressynapomorphies that identify it as a monophyletic group The origin and early evolution of animals was based on four aspects of the fundamental architecture or body plan of animals 1The origin and elaboration of tissuesespecially the tissues found in embryos2The origin and elaboration of the nervous system and the subsequent evolution of a cephalized bodyone with a distinctive head region3The evolution of a fluid filled body cavity4Variation in the events of early embryonic developmentAll animals have groups of similar cells that are organized into the tightly integrated structural and functional units called tissuesAlthough sponges lack many types of tissues found in other animals recent research has shown that one group of sponges has epitheliuma layer of tightly joined cells that covers the surface In animals other than sponges the number of tissues that exist in an embryo varies Animals whose embryos have two types of tissue are called diploblasts animals whose embryos have three types are called triploblasts Embryonic tissues are organized in layers called germ layers In diploblasts these germ layers are called ectoderm and endodermIn most cases the outer and inner skins of diploblast embryos are connected by a gelatinous material that may contain some cells In triploblasts however there is a germ layer called mesoderm between the ectoderm and endodermThe embryonic tissues found in animals develop into distinct adult tissues organs and organ systems In triploblasts for exampleEctoderm gives rise to skin and the nervous systemEndoderm gives rise to the lining of the digestive tractMesoderm gives rise to the circulatory system muscle and internal structures such as bone and most organsIn general then ectoderm produces the covering of the animal and endoderm generates the digestive tract Mesoderm gives rise to the tissues in between The same pattern holds in diploblasts except that1Muscle is simpler in organization and is derived from ectoderm2Reproductive tissues are derived from endodermTraditionally two groups of animals have been recognized as diploblasts the Cnidariawhich include the jellyfish corals sea pens hydra and anemonesand the Ctenophora or comb jellies At least some cnidarians have mesoderm and are triploblastic All other animals from leeches to humans are triploblastic The evolution of mesoderm was important because it gave rise to the first complex muscle tissue used in movement Sponges lack muscle and are sessile or nonmoving as adults their larvae immature forms move via cilia Ctenophores have muscle cells that can change the bodys shape but both larvae and adults swim using cilia Sponges lack neurons but cnidarians and ctenophores have nerve cells that are organized into a diffuse arrangement called a nerve net
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